Drug · FAERS side-effect profile with label screen
Mechlorethamine side effects: what 2,244 FDA adverse event reports show
Drug class
Alkylating Drug
FDA label (Established Pharmacologic Class) of the closest related product
Label matched
Mechlorethamine Hydrochloride (Valchlor)
closest FDA label found for this product string; brand list suppressed because the label is a related product, not an exact match
Who reports
2,244 reports · 32% serious · 154 with death outcome · 47% female
openFDA FAERS counts, all years, deduplication not applied
Used for
VALCHLOR is indicated for the topical treatment of Stage IA and IB mycosis fungoides-type cutaneous T-cell lymphoma in patients who have received prior skin-directed therapy. VALCHLOR is an alkylating drug indicated for the topical treatment of Stage IA and IB mycosis fungoides-type cutaneous T-cell lymphoma in patients who have received prior skin-directed therapy ( 1 ).
FDA label, Indications and Usage
What it is
VALCHLOR is a topical product that contains mechlorethamine HCl, an alkylating drug. Mechlorethamine HCl is a white to off white solid that is very soluble in water and methanol, partially soluble in acetone, and generally not soluble in organic solvents.
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 40 strongest signals
Labeled adverse reaction 5Labeled (related wording) 4Likely indication confounding 3Reporting / coding artifact 9Not in label — unassessed 19
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.
- Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
- Likely indication confounding The term appears in the label's indications: reports probably describe the disease being treated (or its progression), not a drug effect. Classic confounding by indication.
- Reporting / coding artifact An administrative, monitoring or exposure term (product issue, off-label use, 'test normal', overdose...). Not a biological reaction; a high PRR here reflects how reports are coded.
- 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. 16 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.
Show:
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Application site pain | 218 | 93.4 82.3–106.1ROR 103.4 · χ² 19,667 / p <1e-300 | 91.8 EB05 82.0 · IC025 +6.0 3/3 methods agree | Labeled (related wording) related wording | serious n=43 | no trial data cached |
| Application site pruritus | 224 | 93.1 82.2–105.5ROR 103.4 · χ² 20,143 / p <1e-300 | 91.5 EB05 81.9 · IC025 +6.0 3/3 methods agree | Labeled (related wording) related wording | serious n=39 | no trial data cached |
| Application site erythema | 220 | 78.8 69.4–89.4ROR 87.2 · χ² 16,694 / p <1e-300 | 77.6 EB05 69.4 · IC025 +5.8 3/3 methods agree | Not in label — unassessed | serious n=49 | no trial data cached |
| Application site irritation | 101 | 76.5 63.1–92.6ROR 80.0 · χ² 7,389 / p <1e-300 | 74.8 EB05 63.3 · IC025 +5.5 3/3 methods agree | Not in label — unassessed | serious n=22 | no trial data cached |
| Application site rash | 47 | 31.9 24.1–42.4ROR 32.6 · χ² 1,374 / p <1e-300 | 31.5 EB05 24.6 · IC025 +4.1 3/3 methods agree | Not in label — unassessed | serious n=20 | no trial data cached |
| Skin discolouration | 147 | 30.0 25.6–35.1ROR 32.0 · χ² 4,086 / p <1e-300 | 29.8 EB05 26.0 · IC025 +4.5 3/3 methods agree | Not in label — unassessed | serious PRR 17.1 | no trial data cached |
| Scab | 34 | 28.1 20.1–39.3ROR 28.5 · χ² 860 / p 3e-189 | 27.6 EB05 20.7 · IC025 +3.8 3/3 methods agree | Not in label — unassessed | serious n=8 | no trial data cached |
| Intentional dose omission | 79 | 27.1 21.8–33.6ROR 28.0 · χ² 1,954 / p <1e-300 | 26.8 EB05 22.2 · IC025 +4.2 3/3 methods agree | Reporting / coding artifact | serious PRR 61.2 · 94% consumer | no trial data cached |
| No therapeutic response | 34 | 25.7 18.4–36.0ROR 26.1 · χ² 782 / p 2e-172 | 25.4 EB05 19.0 · IC025 +3.7 3/3 methods agree | Reporting / coding artifact | serious PRR 3.8 · 100% clinician | no trial data cached |
| Skin irritation | 112 | 22.9 19.1–27.4ROR 24.0 · χ² 2,319 / p <1e-300 | 22.7 EB05 19.4 · IC025 +4.1 3/3 methods agree | Not in label — unassessed | serious n=20 | no trial data cached |
| Skin lesion | 62 | 21.3 16.7–27.3ROR 21.9 · χ² 1,180 / p 8e-259 | 21.2 EB05 17.1 · IC025 +3.8 3/3 methods agree | Not in label — unassessed | serious PRR 25.4 | no trial data cached |
| Dermatitis contact | 22 | 18.1 12.0–27.5ROR 18.3 · χ² 339 / p 6e-76 | 17.7 EB05 12.2 · IC025 +3.0 3/3 methods agree | Labeled (related wording) related wording | serious n=7 · 95% clinician | no trial data cached |
| Blister | 107 | 17.9 14.9–21.5ROR 18.7 · χ² 1,689 / p <1e-300 | 17.8 EB05 15.1 · IC025 +3.7 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 10.5 | no trial data cached |
| Dermatitis | 39 | 17.6 12.9–24.1ROR 17.9 · χ² 594 / p 1e-131 | 17.4 EB05 13.2 · IC025 +3.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 20.0 | no trial data cached |
| Skin reaction | 26 | 17.3 11.8–25.4ROR 17.5 · χ² 383 / p 2e-85 | 17.0 EB05 12.0 · IC025 +3.1 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 12.3 | no trial data cached |
| Pain of skin | 49 | 17.0 12.9–22.4ROR 17.3 · χ² 721 / p 4e-159 | 16.8 EB05 13.2 · IC025 +3.4 3/3 methods agree | Labeled (related wording) related wording | serious PRR 24.0 | no trial data cached |
| Therapy non-responder | 74 | 15.5 12.4–19.4ROR 16.0 · χ² 992 / p 4e-218 | 15.4 EB05 12.7 · IC025 +3.4 3/3 methods agree | Reporting / coding artifact | serious PRR 8.1 · 96% clinician | no trial data cached |
| Skin fissures | 25 | 12.4 8.4–18.3ROR 12.5 · χ² 250 / p 1e-56 | 11.8 EB05 8.0 · IC025 +2.7 3/3 methods agree | Not in label — unassessed | serious n=6 | no trial data cached |
| Skin burning sensation | 89 | 11.7 9.5–14.3ROR 12.1 · χ² 862 / p 7e-190 | 11.5 EB05 9.6 · IC025 +3.1 3/3 methods agree | Not in label — unassessed | serious PRR 29.5 | no trial data cached |
| Skin ulcer | 32 | 11.6 8.2–16.4ROR 11.7 · χ² 299 / p 2e-67 | 11.1 EB05 8.0 · IC025 +2.7 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 11.4 | no trial data cached |
| Skin haemorrhage | 16 | 10.4 6.4–16.9ROR 10.4 · χ² 126 / p 1e-29 | 9.1 EB05 5.6 · IC025 +2.2 3/3 methods agree | Not in label — unassessed | serious n=4 | no trial data cached |
| Erythema (skin redness) | 213 | 9.7 8.5–11.0ROR 10.6 · χ² 1,669 / p <1e-300 | 9.6 EB05 8.6 · IC025 +3.0 3/3 methods agree | Not in label — unassessed | serious PRR 7.0 | no trial data cached |
| Skin disorder | 34 | 9.6 6.8–13.3ROR 9.7 · χ² 252 / p 4e-57 | 8.9 EB05 6.5 · IC025 +2.5 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 6.2 | no trial data cached |
| Therapy partial responder | 15 | 9.3 5.6–15.4ROR 9.4 · χ² 103 / p 2e-24 | 7.9 EB05 4.9 · IC025 +2.0 3/3 methods agree | Reporting / coding artifact | serious PRR 12.3 | no trial data cached |
| Wound | 25 | 8.4 5.7–12.4ROR 8.5 · χ² 156 / p 4e-36 | 7.6 EB05 5.3 · IC025 +2.2 3/3 methods agree | Not in label — unassessed | serious PRR 4.4 | no trial data cached |
| Rash papular | 20 | 8.3 5.4–12.9ROR 8.4 · χ² 122 / p 1e-28 | 7.3 EB05 4.9 · IC025 +2.1 3/3 methods agree | Not in label — unassessed | serious PRR 3.8 | no trial data cached |
| Pruritus (itching) | 322 | 8.0 7.2–8.8ROR 9.1 · χ² 1,989 / p <1e-300 | 7.9 EB05 7.2 · IC025 +2.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 6.2 | no trial data cached |
| Skin exfoliation | 70 | 7.9 6.3–9.9ROR 8.1 · χ² 415 / p 2e-92 | 7.6 EB05 6.2 · IC025 +2.5 3/3 methods agree | Not in label — unassessed | serious PRR 13.3 | no trial data cached |
| Disease progression | 99 | 7.9 6.5–9.5ROR 8.2 · χ² 588 / p 4e-130 | 7.6 EB05 6.4 · IC025 +2.6 3/3 methods agree | Reporting / coding artifact | serious PRR 7.5 | no trial data cached |
| Treatment noncompliance | 44 | 7.6 5.7–10.1ROR 7.7 · χ² 245 / p 2e-55 | 7.1 EB05 5.5 · IC025 +2.3 3/3 methods agree | Reporting / coding artifact | serious PRR 6.8 | no trial data cached |
| Dry skin | 97 | 6.9 5.7–8.4ROR 7.2 · χ² 486 / p 6e-108 | 6.7 EB05 5.6 · IC025 +2.4 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 12.3 | no trial data cached |
| Sleep disorder due to a general medical condition | 11 | 6.4 3.5–11.5ROR 6.4 · χ² 44 / p 1e-11 | 5.2 EB05 3.1 · IC025 +1.3 3/3 methods agree | Not in label — unassessed | serious PRR 8.3 | no trial data cached |
| Expired product administered | 22 | 6.2 4.1–9.4ROR 6.3 · χ² 91 / p 8e-22 | 5.5 EB05 3.8 · IC025 +1.8 3/3 methods agree | Reporting / coding artifact | serious n=2 | no trial data cached |
| Condition aggravated | 194 | 6.0 5.3–6.9ROR 6.5 · χ² 816 / p 1e-179 | 5.9 EB05 5.3 · IC025 +2.3 3/3 methods agree | Reporting / coding artifact | serious PRR 5.6 | no trial data cached |
| Malignant neoplasm progression | 63 | 5.8 4.5–7.4ROR 5.9 · χ² 245 / p 1e-55 | 5.6 EB05 4.5 · IC025 +2.1 3/3 methods agree | Reporting / coding artifact | serious PRR 10.5 | no trial data cached |
| Rash macular | 20 | 5.4 3.5–8.3ROR 5.4 · χ² 67 / p 1e-16 | 4.8 EB05 3.3 · IC025 +1.5 3/3 methods agree | Not in label — unassessed | serious PRR 3.6 | no trial data cached |
| Rash pruritic | 28 | 4.9 3.4–7.0ROR 4.9 · χ² 82 / p 7e-20 | 4.5 EB05 3.3 · IC025 +1.6 3/3 methods agree | Not in label — unassessed | serious PRR 3.4 | no trial data cached |
| Skin cancer | 11 | 4.8 2.6–8.6ROR 4.8 · χ² 29 / p 3e-8 | 4.0 EB05 2.4 · IC025 +1.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 8.8 | no trial data cached |
| Burning sensation | 32 | 4.3 3.0–6.0ROR 4.3 · χ² 77 / p 9e-19 | 4.0 EB05 3.0 · IC025 +1.4 3/3 methods agree | Not in label — unassessed | serious PRR 2.1 | no trial data cached |
| Neoplasm malignant | 24 | 3.4 2.3–5.0ROR 3.4 · χ² 38 / p 4e-10 | 3.2 EB05 2.3 · IC025 +1.0 3/3 methods agree | Not in label — unassessed | serious PRR 6.2 · 75% consumer | 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 |
|---|---|---|---|---|---|---|
| Pruritus (itching) | 322 | 8.0 7.2–8.8ROR 9.1 · χ² 1,989 / p <1e-300 | 7.9 EB05 7.2 · IC025 +2.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 6.2 | no trial data cached |
| Application site pruritus | 224 | 93.1 82.2–105.5ROR 103.4 · χ² 20,143 / p <1e-300 | 91.5 EB05 81.9 · IC025 +6.0 3/3 methods agree | Labeled (related wording) related wording | serious n=39 | no trial data cached |
| Application site erythema | 220 | 78.8 69.4–89.4ROR 87.2 · χ² 16,694 / p <1e-300 | 77.6 EB05 69.4 · IC025 +5.8 3/3 methods agree | Not in label — unassessed | serious n=49 | no trial data cached |
| Application site pain | 218 | 93.4 82.3–106.1ROR 103.4 · χ² 19,667 / p <1e-300 | 91.8 EB05 82.0 · IC025 +6.0 3/3 methods agree | Labeled (related wording) related wording | serious n=43 | no trial data cached |
| Erythema (skin redness) | 213 | 9.7 8.5–11.0ROR 10.6 · χ² 1,669 / p <1e-300 | 9.6 EB05 8.6 · IC025 +3.0 3/3 methods agree | Not in label — unassessed | serious PRR 7.0 | no trial data cached |
| Condition aggravated | 194 | 6.0 5.3–6.9ROR 6.5 · χ² 816 / p 1e-179 | 5.9 EB05 5.3 · IC025 +2.3 3/3 methods agree | Reporting / coding artifact | serious PRR 5.6 | no trial data cached |
| Skin discolouration | 147 | 30.0 25.6–35.1ROR 32.0 · χ² 4,086 / p <1e-300 | 29.8 EB05 26.0 · IC025 +4.5 3/3 methods agree | Not in label — unassessed | serious PRR 17.1 | no trial data cached |
| Skin irritation | 112 | 22.9 19.1–27.4ROR 24.0 · χ² 2,319 / p <1e-300 | 22.7 EB05 19.4 · IC025 +4.1 3/3 methods agree | Not in label — unassessed | serious n=20 | no trial data cached |
| Blister | 107 | 17.9 14.9–21.5ROR 18.7 · χ² 1,689 / p <1e-300 | 17.8 EB05 15.1 · IC025 +3.7 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 10.5 | no trial data cached |
| Application site irritation | 101 | 76.5 63.1–92.6ROR 80.0 · χ² 7,389 / p <1e-300 | 74.8 EB05 63.3 · IC025 +5.5 3/3 methods agree | Not in label — unassessed | serious n=22 | no trial data cached |
| Disease progression | 99 | 7.9 6.5–9.5ROR 8.2 · χ² 588 / p 4e-130 | 7.6 EB05 6.4 · IC025 +2.6 3/3 methods agree | Reporting / coding artifact | serious PRR 7.5 | no trial data cached |
| Dry skin | 97 | 6.9 5.7–8.4ROR 7.2 · χ² 486 / p 6e-108 | 6.7 EB05 5.6 · IC025 +2.4 3/3 methods agree | Likely indication confounding term in indications; also in warnings | serious PRR 12.3 | no trial data cached |
| Skin burning sensation | 89 | 11.7 9.5–14.3ROR 12.1 · χ² 862 / p 7e-190 | 11.5 EB05 9.6 · IC025 +3.1 3/3 methods agree | Not in label — unassessed | serious PRR 29.5 | no trial data cached |
| Intentional dose omission | 79 | 27.1 21.8–33.6ROR 28.0 · χ² 1,954 / p <1e-300 | 26.8 EB05 22.2 · IC025 +4.2 3/3 methods agree | Reporting / coding artifact | serious PRR 61.2 · 94% consumer | no trial data cached |
| Therapy non-responder | 74 | 15.5 12.4–19.4ROR 16.0 · χ² 992 / p 4e-218 | 15.4 EB05 12.7 · IC025 +3.4 3/3 methods agree | Reporting / coding artifact | serious PRR 8.1 · 96% clinician | no trial data cached |
Unlabeled candidate signals
These flagged terms were not found in the FDA label text and do not match an artifact pattern. They are the pairs that would merit a structured assessment (temporality, dose-response, biological plausibility, consistency across databases, trial or cohort evidence). The screen has not done that; string-matching misses label wording, and a strong PRR can still be stimulated reporting, co-medication, or the disease itself.
- Application site erythema — n=220, PRR 78.8
- Application site irritation — n=101, PRR 76.5
- Application site rash — n=47, PRR 31.9
- Skin discolouration — n=147, PRR 30.0
- Scab — n=34, PRR 28.1
- Skin irritation — n=112, PRR 22.9
- Skin lesion — n=62, PRR 21.3
- Skin fissures — n=25, PRR 12.4
- Skin burning sensation — n=89, PRR 11.7
- Erythema — n=213, PRR 9.7
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 Mechlorethamine?
In FDA FAERS, the most frequently co-reported reaction terms for Mechlorethamine are pruritus, application site pruritus, application site erythema, application site pain, erythema, skin discolouration. 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 Mechlorethamine have an FDA boxed warning?
No. The FDA label retrieved for Mechlorethamine has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Mechlorethamine 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 6a52e4c2-6a9f-4ebb-bc77-046b4f8bcd57, effective 20241120; matched on
openfda.generic_name.exact:"MECHLORETHAMINE HYDROCHLORIDE") - 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, fieldpatient.drug.openfda.generic_name.exact, 56 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.