Chlorhexidine reduces COVID-19 risk: real-time meta analysis of 5 studies
ControlAbstract
Significantly lower risk is seen for progression, cases, and viral clearance. 5 studies from 5 independent teams in 5 countries show significant
benefit.
Meta analysis using the most serious outcome reported shows
71% [57‑80%] lower risk. Results are similar for Randomized Controlled Trials.
Currently there is limited data, with only 722 patients in trials to date.
4 RCTs
with 512 patients have not reported results (up to 3 years late).
No treatment is 100%
effective. Protocols combine safe and effective options with individual
risk/benefit analysis and monitoring.
Chlorhexidine may be detrimental to the natural microbiome, raising concern for side effects, especially with prolonged or excessive use.
All data and sources to reproduce this analysis are in the appendix.
Chlorhexidine for COVID-19 — Highlights
Chlorhexidine reduces risk with very high confidence for viral clearance and in pooled analysis, and low confidence for progression and cases.
50th treatment shown effective in November 2023, now with p = 0.00000000075 from 5 studies.
Real-time updates and corrections with a consistent protocol for 161 treatments. Outcome specific analysis and combined evidence from all studies including treatment delay, a primary confounding factor.
Figure 1.
A. Random effects
meta-analysis. This plot shows pooled effects,
see the specific outcome analyses for individual outcomes.
Analysis validating pooled outcomes for
COVID-19 can be found below.
Effect extraction is pre-specified, using the most serious outcome reported.
For details see the appendix.
B. Timeline of results in chlorhexidine studies. The marked dates indicate the time when efficacy was known with a statistically significant improvement of ≥10% from ≥3 studies for pooled outcomes, one or more specific outcome, and pooled outcomes in RCTs. Efficacy based on RCTs only was delayed by 1.6 months, compared to using all studies. Efficacy based on specific outcomes was delayed by 17.3 months, compared to using pooled outcomes.
Naso/oropharyngeal treatments
AlkalinizationAstodrimer Sodium
Cetylpyridin..
Chlorhexidine
Chlorphenira..
Hydrogen Per..
Iota-carragee..
Nitric Oxide
Phthalocyan..
Plasma-activ..
Povidone-Iod..
Sentinox
Sodium Bicar..
pHOXWELL
SARS-CoV-2 infection typically starts in the upper respiratory
tract, and specifically the nasal respiratory epithelium. Entry via the eyes
and gastrointestinal tract is possible, but less common, and entry via other
routes is rare.
Infection may progress to the lower respiratory tract, other tissues, and the
nervous and cardiovascular systems. The primary initial route for entry into
the central nervous system is thought to be the olfactory nerve in the nasal
cavity1.
Progression may lead to cytokine storm, pneumonia, ARDS, neurological
injury2-14 and cognitive
deficits5,10, cardiovascular
complications15-19, organ failure, and death.
Systemic treatments may be insufficient to prevent
neurological damage9.
Minimizing replication as early as possible is recommended.
Logically, stopping replication in the upper respiratory tract should be
simpler and more effective.
Wu et al., using an airway organoid model incorporating many in
vivo aspects, show that SARS-CoV-2 initially attaches to cilia —
hair-like structures responsible for moving the mucus layer and where ACE2 is
localized in nasal epithelial cells22. The mucus layer and the
need for ciliary transport slow down infection, providing more time for
localized treatments20,21.
Early or prophylactic nasopharyngeal/oropharyngeal treatment may avoid the
consequences of viral replication in other tissues, and avoid the requirement
for systemic treatments with greater potential for side effects.
SARS-CoV-2 infection and replication involves the complex interplay of 100+
host and viral proteins and other factorsA,23-30, providing many
therapeutic targets for which many existing compounds have known activity.
Scientists have predicted that over 9,000 compounds may
reduce COVID-19 risk31, either by
directly minimizing infection or replication, by supporting immune system
function, or by minimizing secondary complications.
We analyze all significant
controlled studies of
chlorhexidine
for COVID-19.
Search methods, inclusion criteria, effect extraction criteria (more serious
outcomes have priority), all individual study data, PRISMA answers, and
statistical methods are detailed in Appendix 1. We present random
effects meta-analysis results for all studies, studies within each treatment stage, individual outcomes, and Randomized Controlled Trials (RCTs).
Figure 3 shows stages of possible treatment for
COVID-19. Prophylaxis refers to regularly taking medication before
becoming sick, in order to prevent or minimize infection. Early
Treatment refers to treatment immediately or soon after symptoms appear,
while Late Treatment refers to more delayed treatment.
Figure 3. Treatment stages.
Table 1 summarizes the results for all stages combined, for Randomized Controlled Trials, and for specific outcomes.
Table 2 shows results by treatment stage.
Figure 4 plots individual results by treatment stage.
Figure 5, 6, 7, and 8
show forest plots for random effects meta-analysis of
all studies with pooled effects, progression, cases, and viral clearance.
| Improvement | Studies | Patients | Authors | |
|---|---|---|---|---|
| All studies | 71% [57‑80%] **** | 5 | 722 | 35 |
| Randomized Controlled TrialsRCTs | 75% [67‑80%] **** | 3 | 630 | 13 |
| Viral | 69% [44‑83%] *** | 3 | 386 | 24 |
| Early treatment | Late treatment | Prophylaxis | |
|---|---|---|---|
| All studies | 73% [38‑88%] ** | 75% [66‑81%] **** | 61% [3‑84%] * |
| Randomized Controlled TrialsRCTs | 79% [61‑89%] **** | 75% [66‑81%] **** | 61% [3‑84%] * |
| Viral | 78% [-91‑98%] | 75% [66‑81%] **** |
Figure 4. Scatter plot showing the most serious outcome in all studies, and for studies within each stage. Diamonds shows the results of random effects meta-analysis.
Figure 5. Random effects meta-analysis for all studies.
This plot shows pooled effects,
see the specific outcome analyses for individual outcomes.
Analysis validating pooled outcomes for
COVID-19 can be found below.
Effect extraction is pre-specified, using the most serious outcome reported.
For details see the appendix.
Figure 6. Random effects meta-analysis for progression.
Figure 7. Random effects meta-analysis for cases.
Figure 8. Random effects meta-analysis for viral clearance.
Figure 9 shows a comparison of results for RCTs and non-RCT studies.
Figure 10 shows a forest plot for random
effects meta-analysis of all Randomized Controlled Trials.
RCT results are included in Table 1 and Table 2.
Figure 9. Results for RCTs and non-RCT studies.
Figure 10. Random effects meta-analysis for all Randomized Controlled Trials.
This plot shows pooled effects,
see the specific outcome analyses for individual outcomes.
Analysis validating pooled outcomes for
COVID-19 can be found below.
Effect extraction is pre-specified, using the most serious outcome reported.
For details see the appendix.
RCTs help to make study groups more similar and can provide a higher level of
evidence, however they are subject to many biases33, and
analysis of double-blind RCTs has identified extreme levels of bias34.
For COVID-19, the overhead may delay treatment, dramatically compromising
efficacy; they may encourage monotherapy for simplicity at the cost of
efficacy which may rely on combined or synergistic effects; the participants
that sign up may not reflect real world usage or the population that benefits
most in terms of age, comorbidities, severity of illness, or other factors;
standard of care may be compromised and unable to evolve quickly based on
emerging research for new diseases; errors may be made in randomization and
medication delivery; and investigators may have hidden agendas or vested
interests influencing design, operation, analysis, reporting, and the
potential for fraud. All of these biases have been observed with COVID-19
RCTs. There is no guarantee that a specific RCT provides a higher level of
evidence.
RCTs are expensive and many RCTs are funded
by pharmaceutical companies or interests closely aligned with pharmaceutical
companies. For COVID-19, this creates an incentive to show efficacy for
patented commercial products, and an incentive to show a lack of efficacy for
inexpensive treatments. The bias is expected to be significant, for example
Als-Nielsen et al. analyzed 370 RCTs from Cochrane reviews, showing that
trials funded by for-profit organizations were 5 times more likely to
recommend the experimental drug compared with those funded by nonprofit
organizations. For COVID-19, some major philanthropic organizations are
largely funded by investments with extreme conflicts of interest for and
against specific COVID-19 interventions.
High quality RCTs for novel acute diseases are more challenging, with
increased ethical issues due to the urgency of treatment, increased risk due
to enrollment delays, and more difficult design with a rapidly evolving
evidence base. For COVID-19, the most common site of initial infection is the
upper respiratory tract. Immediate treatment is likely to be most successful
and may prevent or slow progression to other parts of the body. For a
non-prophylaxis RCT, it makes sense to provide treatment in advance and
instruct patients to use it immediately on symptoms, just as some governments
have done by providing medication kits in advance. Unfortunately, no RCTs have
been done in this way. Every treatment RCT to date involves delayed treatment.
Among the 161 treatments we have analyzed,
66% of RCTs involve very late treatment 5+ days after
onset. No non-prophylaxis COVID-19 RCTs match the potential real-world use of
early treatments. They may more accurately represent results for treatments
that require visiting a medical facility, e.g., those requiring intravenous
administration.
For COVID-19, observational study results do not systematically
differ from RCTs, RR 1.00 [0.93‑1.07]
across 161 treatments36.
Evidence shows that observational studies
can also provide reliable results. Concato et al. found that well-designed
observational studies do not systematically overestimate the magnitude of the
effects of treatment compared to RCTs. Anglemyer et al. analyzed reviews
comparing RCTs to observational studies and found little evidence for
significant differences in effect estimates.
We performed a similar analysis across the 161 treatments
we cover, showing no significant difference in the results of RCTs compared to
observational studies, RR 1.00 [0.93‑1.07]. Similar results are found for all low-cost treatments, RR
1.02 [0.93‑1.11]. High-cost treatments
show a non-significant trend towards RCTs showing greater efficacy,
RR 0.93 [0.83‑1.04].
Details can be found in the
supplementary data.
Lee (B) et al. showed that only 14% of the guidelines of the Infectious
Diseases Society of America were based on RCTs. Evaluation of studies relies
on an understanding of the study and potential biases. Limitations in an RCT
can outweigh the benefits, for example excessive dosages, excessive treatment
delays, or remote survey bias may have a greater effect on results. Ethical
issues may also prevent running RCTs for known effective treatments. For more
on issues with RCTs see40,41.
Currently, 53 of the treatments we analyze show statistically significant efficacy or harm, defined as ≥10% decreased risk or >0% increased risk from ≥3 studies. Of these, 58% have been confirmed in RCTs, with a mean delay of 7.8 months (66% with 8.9 months delay for low-cost treatments). The remaining treatments either have no RCTs, or the point estimate is consistent.
We need to evaluate each trial on its own merits. RCTs for a
given medication and disease may be more reliable, however they may also be
less reliable. For off-patent medications, very high conflict of interest
trials may be more likely to be RCTs, and more likely to be large trials that
dominate meta analyses.
Figure 11.
Optimal spray angle may increase nasopharyngeal drug delivery 100x for nasal sprays,
adapted from Akash et al.
In addition to the dosage and frequency of administration,
efficacy for nasopharyngeal/oropharyngeal treatments may depend on many
other details. For example considering sprays, viscosity, mucoadhesion,
sprayability, and application angle are important.
Akash et al. performed a computational fluid dynamics study
of nasal spray administration showing 100x improvement in nasopharyngeal drug
delivery using a new spray placement protocol, which involves holding the spay
nozzle as horizontally as possible at the nostril, with a slight tilt towards
the cheeks. The study also found the optimal droplet size range for
nasopharyngeal deposition was ~7-17µm.
Heterogeneity in COVID-19 studies arises from many factors including:
The time between infection or the onset of symptoms and
treatment may critically affect how well a treatment works. For example an
antiviral may be very effective when used early but may not be effective in
late stage disease, and may even be harmful. Oseltamivir, for example, is
generally only considered effective for influenza when used within 0-36 or
0-48 hours47,48. Baloxavir marboxil studies for influenza
also show that treatment delay is critical — Ikematsu et al. report
an 86% reduction in cases for post-exposure prophylaxis, Hayden et al.
show a 33 hour reduction in the time to alleviation of symptoms for treatment
within 24 hours and a reduction of 13 hours for treatment within 24-48 hours,
and Kumar et al. report only 2.5 hours improvement for inpatient
treatment.
| Treatment delay | Result |
| Post-exposure prophylaxis | 86% fewer cases49 |
| <24 hours | -33 hours symptoms50 |
| 24-48 hours | -13 hours symptoms50 |
| Inpatients | -2.5 hours to improvement51 |
Figure 12 shows a mixed-effects meta-regression for efficacy
as a function of treatment delay in COVID-19 studies from 161 treatments, showing
that efficacy declines rapidly with treatment delay. Early treatment is
critical for COVID-19.
Figure 12. Early treatment is more effective. Meta-regression showing efficacy as a function of treatment delay in COVID-19 studies from 161 treatments.
Details of the patient population including age and comorbidities may
critically affect how well a treatment works. For example, many COVID-19
studies with relatively young low-comorbidity patients show all patients
recovering quickly with or without treatment. In such cases, there is little
room for an effective treatment to improve results, for example as in
López-Medina et al.
Efficacy may depend critically on the distribution of
SARS-CoV-2 variants encountered by patients. Risk varies significantly across
variants53, for example the Gamma variant shows significantly
different characteristics54-57. Different
mechanisms of action may be more or less effective depending on variants, for
example the degree to which TMPRSS2 contributes to viral entry can differ
across variants58,59.
Effectiveness may depend strongly on the dosage and treatment regimen.
The quality of medications may vary significantly between
manufacturers and production batches, which may significantly affect efficacy
and safety. Williams et al. analyze ivermectin from 11 different sources,
showing highly variable antiparasitic efficacy across different manufacturers.
Xu et al. analyze a treatment from two different manufacturers, showing 9
different impurities, with significantly different concentrations for each
manufacturer.
Across all
studies there is a strong association between different outcomes, for example
improved recovery is strongly associated with lower mortality. However,
efficacy may differ depending on the effect measured, for example a treatment
may be more effective against secondary complications and have minimal effect
on viral clearance.
The
distribution of studies will alter the outcome of a meta analysis. Consider a
simplified example where everything is equal except for the treatment delay,
and effectiveness decreases to zero or below with increasing delay. If there
are many studies using very late treatment, the outcome may be negative, even
though early treatment is very effective.
All meta analyses combine heterogeneous studies, varying in population,
variants, and potentially all factors above, and therefore may obscure
efficacy by including studies where treatment is less effective. Generally, we
expect the estimated effect size from meta analysis to be less than that for
the optimal case.
Looking at all studies is valuable for providing an overview of all research,
important to avoid cherry-picking, and informative when a positive result is
found despite combining less-optimal situations. However, the resulting
estimate does not apply to specific cases such as
early treatment in high-risk populations.
While we present results for all studies, we also present treatment time and
individual outcome analyses, which may be more informative for specific use
cases.
This section validates the use of pooled effects for COVID-19, which enables
earlier detection of efficacy, however pooled effects are no longer required
for chlorhexidine as of April 2025. Efficacy is now known based on specific outcomes. Efficacy based on specific outcomes was delayed by 17.3 months compared to using pooled outcomes.
For COVID-19, delay in clinical results translates into
additional death and morbidity, as well as additional economic and societal
damage. Combining the results of studies reporting different outcomes is
required.
There may be no mortality in a trial with low-risk patients,
however a reduction in severity or improved viral clearance may translate
into lower mortality in a high-risk population.
Different studies may report lower severity, improved recovery, and lower mortality,
and the significance may be very high when combining the results.
"The studies reported different outcomes" is not a good reason for
disregarding results.
Pooling the results of studies reporting different outcomes allows us to use
more of the available information. Logically we should, and do, use additional
information when evaluating treatments—for example dose-response and
treatment delay-response relationships provide additional evidence of efficacy
that is considered when reviewing the evidence for a treatment.
We present both specific outcome and pooled analyses.
In order to combine the results of studies reporting different outcomes we use
the most serious outcome reported in each study, based on the thesis that
improvement in the most serious outcome provides comparable measures of
efficacy for a treatment. A critical advantage of this approach is
simplicity and transparency.
There are many other ways to combine evidence for different outcomes, along
with additional evidence such as dose-response relationships, however these
increase complexity.
Trials with high-risk patients may be restricted due to ethics for treatments
that are known or expected to be effective, and they increase difficulty for
recruiting. Using less severe outcomes as a proxy for more serious outcomes
allows faster and safer collection of evidence.
For many COVID-19 treatments, a reduction in mortality logically
follows from a reduction in hospitalization, which follows from a reduction in
symptomatic cases, which follows from a reduction in PCR positivity. We can
directly test this for COVID-19.
Analysis of the the association between different outcomes across studies from
all 161
treatments we cover confirms the validity of pooled outcome analysis for COVID-19.
Figure 13 shows that lower hospitalization is very strongly associated
with lower mortality (p < 0.000000000001).
Similarly, Figure 14 shows that improved recovery is very strongly associated
with lower mortality (p < 0.000000000001).
Considering the extremes, Singh et al. show an association between viral clearance and
hospitalization or death, with p = 0.003 after excluding one large
outlier from a mutagenic treatment, and based on 44 RCTs including 52,384
patients.
Figure 15 shows that improved viral clearance is strongly associated
with fewer serious outcomes. The association is very similar to
Singh et al., with higher confidence due to the larger number of
studies. As with Singh et al., the confidence increases
when excluding the outlier treatment, from p = 0.00000011 to p = 0.0000000048.
Figure 13. Lower hospitalization is associated with lower mortality, supporting pooled outcome analysis.
Figure 14. Improved recovery is associated with lower mortality, supporting pooled outcome analysis.
Figure 13. Improved viral clearance is associated with fewer serious outcomes, supporting pooled outcome analysis.
Currently, 53 of the treatments we analyze show statistically significant efficacy or harm, defined as ≥10% decreased risk or >0% increased risk from ≥3 studies. 90% of these have been confirmed with one or more specific outcomes, with a mean delay of 4.8 months. When restricting to RCTs only, 55% of treatments showing statistically significant efficacy/harm with pooled effects have been confirmed with one or more specific outcomes, with a mean delay of 7.3 months.
Figure 16 shows when treatments were found effective during the
pandemic. Pooled outcomes often resulted in earlier detection of efficacy.
Figure 16. The time when studies showed that
treatments were effective, defined as statistically significant improvement of
≥10% from ≥3 studies.
Pooled results typically show efficacy earlier than specific
outcome results. Results from all studies often shows efficacy much earlier
than when restricting to RCTs.
Results reflect conditions as used in trials to date, these depend on the
population treated, treatment delay, and treatment regimen.
Pooled analysis could hide efficacy, for example a treatment that is
beneficial for late stage patients but has no effect on viral clearance may
show no efficacy if most studies only examine viral clearance. In practice, it
is rare for a non-antiviral treatment to report viral clearance and to not
report clinical outcomes; and in practice other sources of heterogeneity such
as difference in treatment delay is more likely to hide efficacy.
Analysis validates the use of pooled effects and shows significantly faster
detection of efficacy on average.
However, as with all meta analyses, it is important to review the different
studies included. We also present individual outcome analyses, which may be
more informative for specific use cases.
Analysis of short-term changes in viral load using PCR may not detect
effective treatments because PCR is unable to differentiate between intact
infectious virus and non-infectious or destroyed virus particles. For example
Tarragó‐Gil, Alemany perform RCTs with cetylpyridinium chloride
(CPC) mouthwash that show no difference in PCR viral load, however there was
significantly increased detection of SARS-CoV-2 nucleocapsid protein,
indicating viral lysis. CPC inactivates SARS-CoV-2 by degrading its membrane,
exposing the nucleocapsid of the virus. To better estimate changes in viral
load and infectivity, methods like viral culture that can
differentiate intact vs. degraded virus are preferred.
Studies to date use a variety of administration methods to the
respiratory tract, including nasal and oral sprays, nasal irrigation, oral
rinses, and inhalation. Table 4 shows the relative efficacy for
nasal, oral, and combined administration. Combined administration shows the
best results, and nasal administration is more effective than oral. Precise
efficacy depends on the details of administration, e.g., mucoadhesion and
sprayability for sprays.
| Nasal/oral administration to the respiratory tract | Improvement | Studies |
| Oral spray/rinse | 38% [25‑49%] | 11 |
| Nasal spray/rinse | 58% [49‑65%] | 20 |
| Nasal & oral | 91% [74‑97%] | 7 |
Nasopharyngeal/oropharyngeal treatments may not be highly selective. In
addition to inhibiting or disabling SARS-CoV-2, they may also be harmful to
beneficial microbes, disrupting the natural microbiome in the oral cavity and
nasal passages that have important protective and metabolic roles82. This may be
especially important for prolonged use or overuse.
Table 5 summarizes the potential for common
nasopharyngeal/oropharyngeal treatments to affect the natural
microbiome.
| Treatment | Microbiome disruption potential | Notes |
|---|---|---|
| Iota-carrageenan | Low | Primarily antiviral, however extended use may mildly affect the microbiome |
| Nitric Oxide | Low to moderate | More selective towards pathogens, however excessive concentrations or prolonged use may disrupt the balance of bacteria |
| Alkalinization | Moderate | Increases pH, negatively impacting beneficial microbes that thrive in a slightly acidic environment |
| Cetylpyridinium Chloride | Moderate | Quaternary ammonium broad-spectrum antiseptic that can disrupt beneficial and harmful bacteria |
| Phthalocyanine | Moderate to high | Photodynamic compound with antimicrobial activity, likely to affect the microbiome |
| Chlorhexidine | High | Potent antiseptic with broad activity, significantly disrupts the microbiome |
| Hydrogen Peroxide | High | Strong oxidizer, harming both beneficial and harmful microbes |
| Povidone-Iodine | High | Potent broad-spectrum antiseptic harmful to beneficial microbes |
Publishing is often biased
towards positive results, however evidence suggests that there may be a negative bias for
inexpensive treatments for COVID-19. Both negative and positive results are
very important for COVID-19, media in many countries prioritizes negative
results for inexpensive treatments (inverting the typical incentive for
scientists that value media recognition), and there are many reports of
difficulty publishing positive results83-86.
For chlorhexidine, there is currently not
enough data to evaluate publication bias with high confidence.
Pharmaceutical drug
trials often have conflicts of interest whereby sponsors or trial staff have a
financial interest in the outcome being positive. Chlorhexidine for COVID-19
lacks this because it is off-patent, has multiple manufacturers, and is very low cost.
In contrast, most COVID-19 chlorhexidine trials have been run by
physicians on the front lines with the primary goal of finding the best
methods to save human lives and minimize the collateral damage caused by
COVID-19. While pharmaceutical companies are careful to run trials under
optimal conditions (for example, restricting patients to those most likely to
benefit, only including patients that can be treated soon after onset when
necessary, and ensuring accurate dosing), not all chlorhexidine trials
represent the optimal conditions for efficacy.
Summary statistics from
meta analysis necessarily lose information. As with all meta analyses, studies
are heterogeneous, with differences
in treatment delay, treatment regimen, patient demographics, variants,
conflicts of interest, standard of care, and other factors. We provide analyses for specific
outcomes and by treatment delay, and we aim to identify key characteristics in
the forest plots and summaries. Results should be viewed in the context of
study characteristics.
Some analyses classify treatment based on early or late
administration, as done here, while others distinguish between mild, moderate,
and severe cases. Viral load does not indicate degree of symptoms — for
example patients may have a high viral load while being asymptomatic. With
regard to treatments that have antiviral properties, timing of treatment is
critical — late administration may be less helpful regardless of
severity.
Details of treatment delay per patient is often not available.
For example, a study may treat 90% of patients relatively early, but the
events driving the outcome may come from 10% of patients treated very late.
Our 5 day cutoff for early treatment may be too conservative, 5 days may be too late in many cases.
Comparison across treatments is confounded by differences in
the studies performed, for example dose, variants, and conflicts of interest.
Trials with conflicts of interest may use designs better suited to the
preferred outcome.
In some cases, the most serious outcome has very few events,
resulting in lower confidence results being used in pooled analysis, however
the method is simpler and more transparent. This is less critical as the
number of studies increases. Restriction to outcomes with sufficient power may
be beneficial in pooled analysis and improve accuracy when there are few
studies, however we maintain our pre-specified method to avoid any
retrospective changes.
Studies show that combinations of treatments can be highly
synergistic and may result in many times greater efficacy than individual
treatments alone62-78.
Therefore standard of care may be critical and benefits may diminish or
disappear if standard of care does not include certain treatments.
This real-time analysis is constantly updated based on
submissions. Accuracy benefits from widespread review and submission of
updates and corrections from reviewers. Less popular treatments may receive
fewer reviews.
No treatment or intervention is 100% available and
effective for all current and future variants. Efficacy may vary significantly
with different variants and within different populations. All treatments have
potential side effects. Propensity to experience side effects may be predicted
in advance by qualified physicians. We do not provide medical advice. Before
taking any medication, consult a qualified physician who can compare all
options, provide personalized advice, and provide details of risks and
benefits based on individual medical history and situations.
2 of 5 studies
combine treatments. The results of
chlorhexidine
alone may differ.
1 of 3 RCTs use combined treatment.
Currently all studies are peer-reviewed.
SARS-CoV-2 infection and replication involves a complex
interplay of 100+ host and viral proteins and other
factors23-30, providing many therapeutic
targets.
Over 9,000 compounds have been predicted to reduce COVID-19
risk31, either by directly
minimizing infection or replication, by supporting immune system function, or
by minimizing secondary complications.
Figure 17 shows an overview of the results for chlorhexidine
in the context of multiple COVID-19 treatments, and Figure 18 shows a plot
of efficacy vs. cost for COVID-19 treatments.
Figure 17.
Scatter plot showing results within the context of multiple COVID-19 treatments.
Diamonds shows the results of random effects meta-analysis.
0.6% of 9,000+ proposed treatments show efficacy99.
Figure 18. Efficacy vs. cost for COVID-19 treatments.
SARS-CoV-2 infection typically starts in the upper respiratory tract.
Progression may lead to cytokine storm, pneumonia, ARDS, neurological issues,
organ failure, and death. Stopping replication in the upper respiratory tract,
via early or prophylactic nasopharyngeal/oropharyngeal treatment, can avoid
the consequences of progression to other tissues, and avoid the requirement
for systemic treatments with greater potential for side effects.
Studies to date show that chlorhexidine is
an effective treatment for COVID-19.
Significantly lower risk is seen for progression, cases, and viral clearance. 5 studies from 5 independent teams in 5 countries show significant
benefit.
Meta analysis using the most serious outcome reported shows
71% [57‑80%] lower risk. Results are similar for Randomized Controlled Trials.
Currently there is limited data, with only 722 patients in trials to date.
Chlorhexidine may be detrimental to the natural microbiome, raising concern for side effects, especially with prolonged or excessive use.
Prospective study of 61 COVID+ patients showing a significant reduction in viral load and infectivity with a mouthwash containing 0.05% cetylpyridinium chloride (CPC) and 0.05% chlorhexidine digluconate (CHX). Mouthwash containing 0.9% NaCl showed a trend towards lower infectivity. The study only analyzes short-term changes in viral load 30 minutes after treatment.
RCT 294 hospitalized patients in the USA, showing faster oropharyngeal viral clearance with chlorhexidine. Results were better with a combination of oropharyngeal rinse and posterior oropharyngeal spray compared with the rinse alone.
129 patient chlorhexidine early treatment RCT with results not reported over 3 years after completion.
RCT 379 mild COVID-19 cases showing significantly lower prevalence and severity of olfactory and gustatory dysfunction with budesonide nasal spray, chlorhexidine mouthwash, and saline nasal irrigation. The control group received no intervention, the saline group received saline nasal irrigation plus saline nasal spray and mouthwash, and the drug group received saline nasal irrigation plus budesonide nasal spray and chlorhexidine mouthwash. Saline nasal irrigation plus nasal spray and mouthwash were administered once and four times daily, respectively. Both treatment groups had significantly lower prevalence and severity olfactory and gustatory dysfunction. Prevalence was lower for the drug vs. saline group, without statistical significance.
RCT 116 healthcare workers comparing 0.2% chlorhexidine mouthwash (n=36), 7.5% sodium bicarbonate mouthwash (n=40), and placebo (n=40) twice daily for 2 weeks, with symptoms followed for 4 weeks. There were lower symtoms and cases in both treatment groups, with statistical significance for chlorhexidine only. The treatments were stopped after two weeks, results may be better with continued use, more frequent use, and with the addition of nasal use.
245 participant chlorhexidine + PVP-I prophylaxis RCT with results not reported over 2 years after completion.
48 patient chlorhexidine early treatment RCT with results not reported over 3 years after completion.
Prospective study of 45 COVID-19 patients showing improved viral clearance with chlorhexidine gluconate and povidone-iodine mouthwash use.
Estimated 90 patient chlorhexidine early treatment RCT with results not reported over 3 years after estimated completion.
We perform ongoing searches of PubMed, medRxiv, Europe PMC,
ClinicalTrials.gov, The Cochrane Library, Google Scholar, Research
Square, ScienceDirect, Oxford University Press, the reference lists of other
studies and meta-analyses, and submissions to the site c19early.org.
Search terms are chlorhexidine and COVID-19 or SARS-CoV-2. Automated searches are performed twice daily, with all matches reviewed for inclusion.
All studies regarding the use of chlorhexidine for COVID-19 that report
a comparison with a control group are included in the main analysis.
This is a living analysis and is updated regularly.
We extracted effect sizes and associated data from all studies.
If studies report multiple kinds of effects then the most serious
outcome is used in pooled analysis, while other outcomes are included in the
outcome specific analyses. For example, if effects for mortality and cases are
both reported, the effect for mortality is used, this may be different to the
effect that a study focused on.
If symptomatic
results are reported at multiple times, we used the latest time, for example
if mortality results are provided at 14 days and 28 days, the results at 28
days have preference. Mortality alone is preferred over combined outcomes.
Outcomes with zero events in both arms are not used, the next most serious
outcome with one or more events is used. For example, in low-risk populations
with no mortality, a reduction in mortality with treatment is not possible,
however a reduction in hospitalization, for example, is still valuable.
Clinical outcomes are considered more important than viral test status. When
basically all patients recover in both treatment and control groups,
preference for viral clearance and recovery is given to results mid-recovery
where available. After most or all patients have recovered there is little or
no room for an effective treatment to do better, however faster recovery is
valuable.
If only individual symptom data is available, the most serious symptom has
priority, for example difficulty breathing or low SpO2 is more
important than cough.
When results provide an odds ratio, we compute the relative risk when
possible, or convert to a relative risk according to100.
Reported confidence intervals and p-values were used when available,
using adjusted values when provided. If multiple types of adjustments are
reported propensity score matching and multivariable regression has preference
over propensity score matching or weighting, which has preference over
multivariable regression. Adjusted results have preference over unadjusted
results for a more serious outcome when the adjustments significantly alter
results. When needed, conversion between reported p-values and
confidence intervals followed Altman, Altman (B), and Fisher's exact
test was used to calculate p-values for event data. If continuity
correction for zero values is required, we use the reciprocal of the opposite
arm with the sum of the correction factors equal to 1103.
Results are expressed with RR < 1.0 favoring treatment, and using the risk of
a negative outcome when applicable (for example, the risk of death rather than
the risk of survival). If studies only report relative continuous values such
as relative times, the ratio of the time for the treatment group versus the
time for the control group is used. Calculations are done in Python
(3.13.3) with
scipy (1.15.3), pythonmeta (1.26), numpy (2.2.6), statsmodels (0.14.4), and plotly (6.0.1).
Forest plots are computed using PythonMeta104
with the DerSimonian and Laird random effects model (the fixed effect
assumption is not plausible in this case) and inverse variance weighting.
Results are presented with 95% confidence intervals. Heterogeneity among studies was
assessed using the I2 statistic.
Mixed-effects meta-regression results are computed with R (4.4.0) using the metafor
(4.6-0) and rms (6.8-0) packages, and using the most serious sufficiently powered outcome.
For all statistical tests, a p-value less than 0.05 was considered statistically significant.
Grobid 0.8.2 is used to parse PDF documents.
We have classified studies as early treatment if most patients
are not already at a severe stage at the time of treatment (for example based
on oxygen status or lung involvement), and treatment started within 5 days of
the onset of symptoms. If studies contain a mix of early treatment and late
treatment patients, we consider the treatment time of patients contributing
most to the events (for example, consider a study where most patients are
treated early but late treatment patients are included, and all mortality
events were observed with late treatment patients).
We note that a shorter time may be preferable. Antivirals are typically only
considered effective when used within a shorter timeframe, for example 0-36 or
0-48 hours for oseltamivir, with longer delays not being effective47,48.
We received no funding, this research is done in our spare
time. We have no affiliations with any pharmaceutical companies or political
parties.
A summary of study results is below. Please submit
updates and corrections at https://c19early.org/chxmeta.html.
Effect extraction follows pre-specified rules as detailed above
and gives priority to more serious outcomes.
For pooled analyses, the first (most serious) outcome is used, which may
differ from the effect a paper focuses on.
Other outcomes are used in outcome specific analyses.
| Bonn, 3/21/2023, prospective, Germany, peer-reviewed, 14 authors, study period 4 January, 2022 - 22 February, 2022, this trial uses multiple treatments in the treatment arm (combined with CPC) - results of individual treatments may vary, trial DRKS00027812. | viral load, 95.8% lower, relative load 0.04, p = 0.03, treatment median 1.0 IQR 0.5 n=31, control median 24.0 IQR 153.3 n=31, inverted to make RR<1 favor treatment, relative infectious viral load, 30 min vs. baseline, CPC+CHX. |
| viral load, 69.2% lower, relative load 0.31, p = 0.04, treatment 31, control 31, relative PCR viral load, 30 min vs. baseline, CPC+CHX. | Jacox, 10/20/2021, Double Blind Randomized Controlled Trial, USA, trial NCT04584684 (history) (MOR). | 129 patient RCT with results unknown and over 3 years late. |
| Jing, 11/21/2023, Double Blind Randomized Controlled Trial, China, peer-reviewed, 7 authors, study period 5 May, 2022 - 16 June, 2022, this trial uses multiple treatments in the treatment arm (combined with budesonide and saline) - results of individual treatments may vary, trial ChiCTR2200059651. | olfactory or gustatory dysfunction, 79.2% lower, RR 0.21, p < 0.001, treatment 10 of 120 (8.3%), control 56 of 140 (40.0%), NNT 3.2, OGD. |
| VAS olfactory severe, 96.5% lower, RR 0.03, p < 0.001, treatment 0 of 120 (0.0%), control 15 of 140 (10.7%), NNT 9.3, relative risk is not 0 because of continuity correction due to zero events (with reciprocal of the contrasting arm). | |
| VAS gustatory severe, 95.3% lower, RR 0.05, p = 0.001, treatment 0 of 120 (0.0%), control 11 of 140 (7.9%), NNT 13, relative risk is not 0 because of continuity correction due to zero events (with reciprocal of the contrasting arm). | |
| TSS severe, 83.3% lower, RR 0.17, p = 0.07, treatment 1 of 120 (0.8%), control 7 of 140 (5.0%), NNT 24. | Mira, 1/8/2022, Double Blind Randomized Controlled Trial, placebo-controlled, trial NCT05543603 (history). | 48 patient RCT with results unknown and over 3 years late. |
| Sulistyani, 4/30/2025, prospective, Indonesia, peer-reviewed, 8 authors. | viral load, 54.2% lower, relative load 0.46, p = 0.001, treatment 15, control 15, relative increase in Ct value, day 5. | Xie, 2/28/2022, Double Blind Randomized Controlled Trial, placebo-controlled, trial NCT04931004 (history). | Estimated 90 patient RCT with results unknown and over 3 years late. |
Effect extraction follows pre-specified rules as detailed above
and gives priority to more serious outcomes.
For pooled analyses, the first (most serious) outcome is used, which may
differ from the effect a paper focuses on.
Other outcomes are used in outcome specific analyses.
| Huang, 4/30/2021, Randomized Controlled Trial, USA, peer-reviewed, median age 62.0, 2 authors, study period 20 May, 2020 - 15 December, 2020. | risk of no viral clearance, 74.6% lower, RR 0.25, p < 0.001, treatment 38 of 159 (23.9%), control 127 of 135 (94.1%), NNT 1.4, all patients, day 4. |
| risk of no viral clearance, 85.1% lower, RR 0.15, p < 0.001, treatment 13 of 93 (14.0%), control 75 of 80 (93.8%), NNT 1.3, oropharyngeal rinse and spray, day 4. | |
| risk of no viral clearance, 59.9% lower, RR 0.40, p < 0.001, treatment 25 of 66 (37.9%), control 52 of 55 (94.5%), NNT 1.8, oropharyngeal rinse only, day 4. |
Effect extraction follows pre-specified rules as detailed above
and gives priority to more serious outcomes.
For pooled analyses, the first (most serious) outcome is used, which may
differ from the effect a paper focuses on.
Other outcomes are used in outcome specific analyses.
| Karami, 1/9/2024, Double Blind Randomized Controlled Trial, Iran, peer-reviewed, 4 authors, study period July 2022 - October 2022, trial IRCT20220328054364N1. | relative mean total symptoms, 61.0% better, RR 0.39, p = 0.04, treatment mean 1.8 (±3.67) n=36, control mean 4.62 (±7.37) n=40. |
| relative mean week 1 symptoms, 82.0% better, RR 0.18, p = 0.08, treatment mean 0.22 (±1.17) n=36, control mean 1.22 (±3.14) n=40. | |
| relative mean week 2 symptoms, 56.0% better, RR 0.44, p = 0.13, treatment mean 0.66 (±2.05) n=36, control mean 1.5 (±2.63) n=40. | |
| relative mean week 3 symptoms, 11.3% better, RR 0.89, p = 0.84, treatment mean 0.86 (±2.66) n=36, control mean 0.97 (±2.16) n=40. | |
| relative mean week 4 symptoms, 94.6% better, RR 0.05, p = 0.048, treatment mean 0.05 (±0.23) n=36, control mean 0.92 (±2.58) n=40. | |
| risk of case, 56.8% lower, RR 0.43, p = 0.03, treatment 7 of 36 (19.4%), control 18 of 40 (45.0%), NNT 3.9. | Keating, 6/30/2022, Randomized Controlled Trial, USA, this trial uses multiple treatments in the treatment arm (combined with PVP-I) - results of individual treatments may vary, trial NCT04478019 (history) (SHIELD). | 245 patient RCT with results unknown and over 2 years late. |
Viral infection and replication involves attachment, entry, uncoating and release, genome replication and transcription, translation and protein processing, assembly and budding, and release. Each step can be disrupted by therapeutics.
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