Cantharidin side effects: what 166 FDA adverse event reports show

Cantharidin · Ycanth · 4 reaction terms · 87 drug–reaction co-reports · data 2026-09-14

Drug class

Not stated in label

Brand names

Ycanth

openFDA label

Who reports

166 reports · 15% serious · 0 with death outcome · 54% female

openFDA FAERS counts, all years, deduplication not applied

Used for

YCANTH is indicated for the topical treatment of molluscum contagiosum in adult and pediatric patients 2 years of age and older. YCANTH is indicated for the topical treatment of molluscum contagiosum in adult and pediatric patients 2 years of age and older. ( 1 )

FDA label, Indications and Usage

What it is

YCANTH (cantharidin) topical solution is a light violet to dark purple, slightly viscous liquid for topical administration.

FDA label, Description section

Boxed warning

None in the current label

How to read this page. FAERS is a spontaneous-reporting system: counts are not incidence rates and a signal is not proof of causation. Each reaction below is run through an automated screen — is the term in the FDA label (known), in the indications (the disease being treated), an administrative/coding term, or none of these (unlabeled)? That screen is mechanical text matching, not a causality assessment. The 30 hand-written Bradford Hill assessments are on the causality assessment page. Not medical advice.

Causality screen of the 3 strongest signals

Labeled adverse reaction 3

What the badges mean

Labeled adverse reaction The exact term appears in the label's warnings or adverse-reactions sections: a known, expected effect. The FAERS signal confirms the label rather than discovering anything.
Not in label — unassessed Not found in the label text, not an artifact pattern. This is a genuine candidate for a formal causality assessment (Bradford Hill / WHO-UMC); it has NOT had one here.

Strongest disproportionality signals

Flagged terms (PRR ≥ 2, χ² ≥ 4, n ≥ 10), ranked by PRR; infinite PRRs (no comparator reports) excluded. The EBGM column is a second, shrinkage-based estimate (MGPS) with its 5th percentile EB05 and the BCPNN IC025; a pair flagged by PRR alone is marked PRR-only and should be read as fragile. The strata column recomputes the PRR on serious reports only and flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 1 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.

Show: hide coding/lab/outcome terms hide indication terms unlabeled only hide PRR-only

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Application site pain	47	270.2 212.1–344.4ROR 376.6 · χ² 12,325 / p <1e-300	243.0 EB05 190.1 · IC025 +5.7 3/3 methods agree	Labeled adverse reaction exact term	serious n=2	no trial data cached
Blister	30	67.7 48.9–93.6ROR 82.4 · χ² 1,909 / p <1e-300	65.0 EB05 47.7 · IC025 +4.4 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 85.6	no trial data cached
Application site erythema	6	28.8 13.1–63.2ROR 29.8 · χ² 135 / p 2e-31	25.7 EB05 11.3 · IC025 +1.8 3/3 methods agree	Labeled adverse reaction exact term	serious n=2	no trial data cached

Trial evidence (ClinicalTrials.gov)

Trial cross-check not yet run for this drug (ClinicalTrials.gov pull covers the 800 most-reported drugs first).

Most frequently reported reactions

By raw co-report count, regardless of disproportionality. Common terms here are often the illness itself or generic outcomes.

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Application site pain	47	270.2 212.1–344.4ROR 376.6 · χ² 12,325 / p <1e-300	243.0 EB05 190.1 · IC025 +5.7 3/3 methods agree	Labeled adverse reaction exact term	serious n=2	no trial data cached
Blister	30	67.7 48.9–93.6ROR 82.4 · χ² 1,909 / p <1e-300	65.0 EB05 47.7 · IC025 +4.4 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 85.6	no trial data cached
Application site erythema	6	28.8 13.1–63.2ROR 29.8 · χ² 135 / p 2e-31	25.7 EB05 11.3 · IC025 +1.8 3/3 methods agree	Labeled adverse reaction exact term	serious n=2	no trial data cached
Application site pruritus	4	22.3 8.5–58.6ROR 22.8 · χ² 61 / p 2e-15	16.2 EB05 4.3 · IC025 +1.0 3/3 methods agree	Labeled adverse reaction exact term	serious n=1	no trial data cached

Unlabeled candidate signals

Every screened signal with n ≥ 20 was either labeled, an indication term, or an artifact pattern — no unlabeled candidate stood out in the top signals.

Want to assess one of these properly? The runbook describes the Bradford Hill / trial-evidence workflow used on the assessment page, and handoff_top1000_signals.csv lists the strongest unassessed pairs across all drugs.

Common questions

What are the most reported side effects of Cantharidin?

In FDA FAERS, the most frequently co-reported reaction terms for Cantharidin are application site pain, blister, application site erythema, application site pruritus. These are report counts, not rates: FAERS has no denominator, reporting is voluntary and uneven, and a term can be reported because of the illness being treated rather than the drug.

Does Cantharidin have an FDA boxed warning?

No. The FDA label retrieved for Cantharidin has no boxed warning; see the label's Warnings and Precautions for the recognised risks.

Do FAERS signals prove that Cantharidin causes these side effects?

No. A disproportionality signal (PRR, ROR) means a reaction is reported more often with this drug than with others in the database. That can reflect a real effect, but also the disease being treated, stimulated reporting after news or litigation, co-medications, or how reports are coded. Causality needs temporality, dose-response, biological plausibility, consistency across data sources and, ideally, trial or cohort evidence. This page screens each term against the FDA label and ClinicalTrials.gov results; it does not establish causation.

Sources & methods

FDA label via openFDA (set ID 7c9bdeaa-9822-4c69-a719-ea4a8643f59c, effective 20241113; matched on openfda.generic_name.exact:"CANTHARIDIN")
Bayesian shrinkage measures computed offline over all 1,317,300 cached pairs: BCPNN information component (IC, with Norén closed-form IC025) and MGPS empirical-Bayes geometric mean (EBGM, EB05) with a two-component gamma prior fitted by maximum marginal likelihood (α₁=0.57, β₁=0.02, α₂=1.42, β₂=0.70, w=0.17); unstratified
FAERS pair statistics from the OpenPV build of 2026-09-14 (openFDA count= aggregation, field patient.drug.openfda.generic_name.exact, 4 reaction terms, min 3 co-reports); PRR/ROR with 95% CI, chi-square with Yates correction
Serious-only and stratified counts (serious:1, patient.patientsex, primarysource.qualification) from openFDA count queries; serious-only PRR uses the drug serious report total and the term global serious total (N_serious=11,882,979); strata shown only when n ≥ 20
Seriousness and sex counts from openFDA count=serious, patient.patientsex, seriousnessdeath

Page generated 2026-10-08. Label and PubChem text are retrieved automatically and may lag the current label; always check the current prescribing information. OpenPV is a beta research tool of the Open Source Medicine Foundation.