Snake Grass for Herpes Zoster and Herpes Simplex

This is the claim that actually has trial data behind it, and the only one of snake grass’s uses that a national regulator has approved. That makes it worth reading closely rather than waving through, because “there are randomised trials” and “the trials clearly show a benefit” are not the same sentence, and the gap between them here is smaller than for most herbs on this site but not zero.

Table of Contents

1. The Claim and Its Regulatory Anchor
2. The 2011 Meta-Analysis, in Full
3. The Two Original Thai Trials
4. A Related but Distinct Data Point: Genital Warts
5. Proposed Mechanism: Phaeophytins and Virucidal Activity
6. The Study That Found No Activity At All
7. What Systemic Antivirals Already Achieve
8. The 72-Hour Window
9. Topical Is Not Systemic
10. Key Research Papers
11. Connections

The Claim and Its Regulatory Anchor

Thailand’s National List of Essential Medicines includes preparations of Clinacanthus nutans — phaya yo — for the topical treatment of herpes lesions: a cream for skin and a glycerin-based solution for the mouth. That is a real, if narrow, regulatory endorsement, and it did not happen by accident. It rests on four small randomised trials run in Thailand between the mid-1990s and the study that pooled them in 2011. This page reads those four trials directly, adds the laboratory work that proposes a mechanism, and reports a negative finding that the herb’s own advocates rarely mention.

The 2011 Meta-Analysis, in Full

Kongkaew and Chaiyakunapruk searched MEDLINE, EMBASE, CINAHL, Cochrane CENTRAL, AMED, the WHO trial registry, ClinicalTrials.gov, and two Thai indexes, from inception to February 2010, with no language restriction, and assessed trial quality with the Jadad scale and Cochrane’s risk-of-bias tool. Four randomised controlled trials met their criteria — 286 patients in total. This is the number worth sitting with: after fifteen years of a folk reputation and a national essential-medicines listing, the entire indexed trial base is four small studies.

The detail that gets lost in every secondary summary, including the one on this site’s main Snake Grass page, is that the four trials split evenly between two different conditions, and the two conditions did not perform equally.

Read plainly: the statistically significant benefit in this meta-analysis belongs to herpes genitalis, not herpes zoster. The zoster point estimate also favours C. nutans (3.21 is a large ratio), but the interval reported crosses the line of no effect, so the trials are too small to call it a real effect with confidence rather than noise. This matters because most secondary sources — including popular summaries and this site’s own main page for the herb — foreground herpes zoster as the flagship indication, on the strength of two trial names (Sangkitporn, Charuwichitratana) that are indeed both zoster trials. The pooled statistical case is, if anything, stronger for genital herpes. Both are real conditions this cream may help with; the confidence should not be distributed the way the folklore distributes it.

The authors’ own conclusion is appropriately hedged: “this meta-analysis and systematic review suggests some beneficial effects” and calls for “more robustly designed trials” on the purified active compounds specifically. That is a genuinely positive but genuinely cautious verdict, and it is now fifteen years old with no larger confirmatory trial having followed it, as far as this page’s search of the indexed literature found.

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The Two Original Thai Trials

The two zoster trials behind the pooled estimate above are small studies from Thai hospital and public-health settings, both published in the 1990s:

• Sangkitporn and colleagues (1995), in the Journal of the Medical Association of Thailand, treated herpes zoster with a C. nutans (“bi phaya yaw”) extract preparation.
• Charuwichitratana and colleagues (1996), in the International Journal of Dermatology, tested a C. nutans cream specifically against herpes zoster lesions.

Both are exactly the kind of small, single-country, pre-CONSORT-era trial that the “old, weak and positive” tier exists for: real randomised comparisons, run by qualified investigators, published in indexed journals — and small, dated, and never independently replicated at larger scale. That they are also the two trials whose pooled zoster result did not reach significance is consistent with their size rather than a mark against the investigators; small trials are exactly where a real effect can fail to clear the statistical bar even when the point estimate is favourable.

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A Related but Distinct Data Point: Genital Warts

Worth including here precisely because it is easy to mis-file. Jiamton and colleagues, at Siriraj Hospital in Bangkok, ran a randomised trial (2018–2019) comparing C. nutans cream against podophyllin, the standard topical treatment, for condyloma acuminata — genital warts. This is caused by human papillomavirus, a completely different virus family from herpes simplex or varicella zoster, and it is not a herpes indication. It belongs on this page only because it is the same cream, tested by the same research tradition, against a real comparator drug, and it is informative about what the cream can and cannot do.

Ten men, each with at least two warts a centimetre apart, had one wart randomised to each treatment, four weeks of treatment, ages 24 to 72, mostly low-risk HPV types (HPV-6, HPV-11). Median clearance was 97% with podophyllin and 82% with C. nutans. The herbal cream worked, to a real and measurable degree, in a properly randomised within-patient comparison — and it worked less well than the standard drug it was tested against, in a trial of ten patients. The paper’s own conclusion is exactly this size: “C. nutans may be an alternative treatment for CA,” not a replacement for one. It is a useful data point for how this plant’s topical antiviral and anti-inflammatory activity behaves under direct comparison with a real drug: real, smaller, and in a very small trial.

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Proposed Mechanism: Phaeophytins and Virucidal Activity

Sakdarat and colleagues isolated three chlorophyll-derived compounds — phaeophytins, structurally related to chlorophyll a and b — from C. nutans leaves and tested them against HSV-1F in cell culture. All three showed anti-herpes activity at sub-toxic concentrations, and the timing of the effect is specific: it acted before viral entry into the host cell, consistent with a virucidal action or interference with viral adsorption or penetration, rather than blocking replication once the virus is already inside a cell.

That is a coherent, plausible mechanism for a topical product applied directly to a lesion, where the extract can plausibly contact free virus at the skin surface before it enters more cells. It is also, by the same logic, a mechanism that would not obviously work as an oral or systemic treatment, where the extract would need to reach circulating or intracellular virus rather than virus sitting on an exposed surface — a distinction taken up in full in the route section below.

A second isolated compound, purpurin-18 phytyl ester — also a chlorophyll derivative — showed anti-biofilm, nitric-oxide-inhibiting and wound-healing activity in a separate study, broadly consistent with the same chemical family doing several related jobs on an open lesion: discouraging microbial colonisation, calming local inflammation, and supporting tissue repair, in addition to whatever direct antiviral action it has. None of this is measured in a living person; it is what the isolated compounds do in a dish and in cell culture.

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The Study That Found No Activity At All

Reported plainly because doctrine on this site requires it: not every laboratory test of this plant against herpesviruses came back positive, and the one that did not is worth naming rather than quietly omitting.

Yoosook and colleagues (1999) tested organic extracts of C. nutans and of a different Acanthaceae species, Barleria lupulina, against HSV-2 — the standard laboratory strain and five clinical isolates — using a plaque-inhibition assay. Barleria lupulina extract showed activity against all five clinical isolates. C. nutans extract showed no activity against any of them. The paper’s own conclusion: “the results suggest a therapeutic potential of B. lupulina but not C. nutans against HSV-2.”

This is a real and specific contradiction, not a rounding error, and it sits alongside the positive phaeophytin result above without either one cancelling the other out. A few honest ways to hold both at once: different extraction solvents pull out different fractions of the same leaf, so “organic extract” in one paper and the chloroform fraction that yielded phaeophytins in another may not contain the same active material in the same concentration; HSV-1 and HSV-2 are related but distinct viruses and an effect against one does not guarantee an effect against the other; and cell-culture antiviral assays are notoriously sensitive to exact assay conditions. What this page will not do is quietly cite the phaeophytin result and never mention that a differently-designed study on a closely related virus, from a well-regarded Thai virology group, found nothing. Readers deciding whether to trust a cream deserve the whole record, and the record here is genuinely mixed at the laboratory level even where the clinical trials lean positive.

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What Systemic Antivirals Already Achieve

The most useful comparison for a herbal topical is not “better than nothing” but “how does it compare with the treatment that actually changes outcomes,” and for herpes zoster that treatment is well characterised. A 2014 Cochrane review of antiviral treatment for preventing postherpetic neuralgia — the persistent nerve pain that is shingles’ worst complication — pooled the oral aciclovir trial evidence; more recent randomised work has compared newer agents such as amenamevir directly against valaciclovir in phase 3 trials, and a 2023 network meta-analysis assessed antiviral agents specifically for herpes-zoster-associated pain in immunocompetent patients.

The consistent finding across this drug-class literature: oral antivirals, started early, measurably reduce the severity and duration of the acute rash and lower the risk of postherpetic neuralgia, in trials an order of magnitude larger than the entire C. nutans evidence base combined. That is the ceiling a topical herbal cream is being compared against. Nothing above suggests C. nutans cream reaches it, and no trial has tried to test the two head-to-head. The honest position is that the cream may help symptomatically and has some trial support for doing so, while the intervention that actually reduces the risk of long-term nerve pain is the oral antiviral, unaffected by which cream is also applied to the skin.

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The 72-Hour Window

This is the single most consequential practical fact on this page, and it has nothing to do with the herb. Oral antiviral therapy for shingles works best, and the postherpetic-neuralgia risk reduction is largest, when treatment starts within 72 hours of the rash appearing. After that window narrows, the achievable benefit shrinks. A reader who spends the first two or three days of a shingles rash deciding whether to try a cream first, before calling a clinician, may lose the period in which the drug that has the strongest evidence does the most good. Applying a soothing topical — herbal or otherwise — is entirely compatible with also starting an oral antiviral the same day; it is not an either/or choice, and treating it as one is the single easiest way this plant’s real but modest evidence could do a reader harm.

Shingles affecting the eye, the ear, or a large body area, or occurring in anyone immunocompromised, is a same-day medical problem regardless of any home treatment in use.

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Topical Is Not Systemic

Every piece of positive evidence on this page — the four pooled RCTs, the two original Thai trials, the condyloma trial, the phaeophytin virucidal mechanism — concerns a cream or topical solution applied directly to a lesion. None of it is evidence for drinking snake-grass juice, taking a leaf capsule, or any other internal use as a treatment for herpes infection of any kind. This is not a pedantic distinction. A virucidal, pre-entry mechanism that plausibly works by contacting free virus on an exposed skin surface is, on its own logic, not a mechanism that predicts an effect from something swallowed and absorbed into the bloodstream, where the virus it would need to reach is inside cells or in nerve ganglia, not sitting exposed on a mucosal surface. Nothing on this page should be read as supporting an oral snake-grass preparation for a herpes diagnosis of any kind; the trial evidence is specifically for the topical product Thailand actually regulates.

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Key Research Papers

All links are live PubMed searches rather than fixed records, pre-checked to confirm each one returns the intended paper.

1. Kongkaew C, Chaiyakunapruk N, “Efficacy of Clinacanthus nutans extracts in patients with herpes infection: systematic review and meta-analysis of randomised clinical trials”, Complementary Therapies in Medicine, 2011 — the pooled analysis this page is built around; run the search and read the abstract’s own numbers.
2. Sangkitporn S et al., treatment of herpes zoster with Clinacanthus nutans (bi phaya yaw) extract, Journal of the Medical Association of Thailand, 1995.
3. Charuwichitratana S et al., herpes zoster treated with Clinacanthus nutans cream, International Journal of Dermatology, 1996.
4. Jiamton S et al., “Efficacy and Safety of Clinacanthus nutans Lindau Cream vs. Podophyllin for the Treatment of Adults with Condyloma Acuminata”, Evidence-Based Complementary and Alternative Medicine, 2022 — the genital-wart trial; note the 97% vs. 82% clearance numbers in the abstract.
5. Sakdarat S et al., “Bioactive constituents from the leaves of Clinacanthus nutans Lindau”, Bioorganic & Medicinal Chemistry, 2009 — the phaeophytin isolation and anti-HSV-1 assay.
6. Yoosook C et al., “Evaluation of anti-HSV-2 activities of Barleria lupulina and Clinacanthus nutans”, Journal of Ethnopharmacology, 1999 — the negative finding for C. nutans against HSV-2; read the abstract’s conclusion directly.
7. Roeslan MO et al., purpurin-18 phytyl ester from Clinacanthus nutans leaves: anti-biofilm, nitric oxide inhibition and wound healing, Biomedicine & Pharmacotherapy, 2019.
8. Lin CM et al., “Antiviral and Immunomodulatory Activities of Clinacanthus nutans (Burm. f.) Lindau”, International Journal of Molecular Sciences, 2023 — a current review of the antiviral literature across virus families.
9. Chen N et al., “Antiviral treatment for preventing postherpetic neuralgia”, Cochrane Database of Systematic Reviews, 2014 — the drug-class ceiling.
10. Kawashima M et al., amenamevir versus valaciclovir, randomised double-blind phase 3 trial for herpes zoster, Journal of Dermatology, 2017.
11. Liu Y et al., network meta-analysis of antiviral agents for herpes-zoster-associated pain in immunocompetent patients, Pain Physician, 2023.
12. Clinacanthus nutans and herpes — the complete indexed literature — run it yourself and see the full return.

Connections

• All Herbs
• Sabah Snake Grass (Clinacanthus nutans) — the main article, with the plant’s full identity, compounds and cautions.
• Snake Grass Benefits Deep Dive — the hub, including the evidence ledger for this set.
• Snake Grass: The Cancer Claim — why the herb’s more famous use has none of this page’s trial support.
• Snake Grass: Anti-Inflammatory and Immune Mechanisms — the C-glycosyl flavones and chlorophyll derivatives behind this page’s proposed mechanism.
• Shingles (Herpes Zoster) — the condition itself, including the 72-hour antiviral window in full clinical detail.
• Herpes Simplex — HSV-1 and HSV-2, the virus behind the genitalis trials.
• Human Papillomavirus (HPV) — the unrelated virus behind the condyloma trial.
• Andrographis Benefits Deep Dive — the other major Southeast Asian Acanthaceae medicinal, with a more developed human trial base for respiratory infection.
• Kacip Fatimah Benefits Deep Dive — another of Malaysia’s flagship herbs, with a similar tradition-versus-trial pattern.
• Immune Boosting — general context for topical and systemic approaches to viral skin infection.

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