What the label lists and what reports show
Cantharidin side effects
Cantharidin's FDA label: “Most common (incidence ≥1%) adverse reactions are the following local skin reactions at the application site: vesiculation, pain, pruritus, scabbing, erythema, discoloration, application site dryness, edema, and erosion.” FAERS holds 166 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is application site vesicles (69 reports).
- No generic listed
Check it at the source: the cantharidin FDA label on DailyMed (effective November 13, 2024, Verrica Pharmaceuticals Inc.); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of YCANTH?YCANTH can cause serious side effects, including: Serious side effects if YCANTH is swallowed or it comes into contact with your mouth or eyes. YCANTH can cause life threatening reactions or death if it gets into your or your child's mouth or is swallowed. These reactions can include: kidney failure blisters and severe damage to your stomach and intestine (intestinal tract) blood clotting problems seizures a certain type of paralysis If you or your child swallow (ingest) YCANTH, contact a Poison Control Center (1-800-222-1222) or go to the nearest hospital emergency room right away. Eye contact reactions. Severe eye injury can happen if YCANTH gets into your eyes. […]
Source: FDA drug label, Verrica Pharmaceuticals Inc., effective November 13, 2024 (SPL set 7c9bdeaa-9822-4c69-a719-ea4a8643f59c), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common (incidence ≥1%) adverse reactions are the following local skin reactions at the application site: vesiculation, pain, pruritus, scabbing, erythema, discoloration, application site dryness, edema, and erosion.
Table 1. Percentage of Subjects with Selected Adverse Reactions (Incidence ≥1%) by Severity in Trial 1 and Trial 2 (Safety Population)
| Preferred Term Name | Mild | Moderate | Severe | Mild | Moderate | Severe |
|---|---|---|---|---|---|---|
| Application site vesicles | 60% | 32% | 4% | 27% | 2% | 0% |
| Application site pain and pain | 41% | 20% | 2% | 16% | 1% | 0% |
| Application site pruritus and pruritus | 47% | 8% | 1% | 30% | 7% | 0% |
| Application site scab and scab | 39% | 9% | 0% | 20% | 1% | 0% |
| Application site erythema and erythema | 24% | 21% | <1% | 20% | 7% | 0% |
| Application site discoloration | 28% | 4% | <1% | 12% | 1% | 0% |
| Application site dryness | 19% | 2% | 0% | 14% | 1% | 0% |
| Application site edema | 7% | 3% | 0% | 3% | 1% | 0% |
| Application site erosion | 6% | 1% | 0% | 1% | 0% | 0% |
| Contact dermatitis | 0% | 1% | 0% | 0% | 0% | 0% |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe following adverse reactions are described elsewhere in the labeling: Local Skin Reactions [see Warnings and Precautions (5.2) ] Most common (incidence ≥1%) adverse reactions are the following local skin reactions at the application site: vesiculation, pain, pruritus, scabbing, erythema, discoloration, application site dryness, edema, and erosion. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Verrica Pharmaceuticals Inc. at 1-877-837-7422 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. Local skin reactions are expected and should be reported if they are severe. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. YCANTH was studied in two randomized, double-blind, placebo-controlled phase 3 trials, Trial 1 (NCT03377790) and Trial 2 (NCT03377803) (n = 266, and n = 262, respectively) in subjects with molluscum contagiosum. Most patients received a single 24-hour dermal administration of YCANTH or vehicle for each lesion every 3 weeks for up to 4 treatments. …
Source: FDA drug label, Verrica Pharmaceuticals Inc., effective November 13, 2024 (SPL set 7c9bdeaa-9822-4c69-a719-ea4a8643f59c), via openFDA; the full label on DailyMed
What do FAERS reports show?
166 reports list cantharidin among the medicines taken, each a report of something that happened, not proof the medicine caused it; 0 are coded as a death and 5 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 21 reactions below, 5 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Cantharidin: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions