What the label lists and what reports show
Chlorambucil side effects
Chlorambucil's FDA label: “The most common side effect is bone marrow suppression, anemia, leukopenia, neutropenia, thrombocytopenia, or pancytopenia.” FAERS holds 3,917 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 neutropenia (275 reports).
- No generic listed
- Boxed warning
Check it at the source: the chlorambucil FDA label on DailyMed (effective January 8, 2025, Waylis Therapeutics LLC); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsThe most common side effect is bone marrow suppression, anemia, leukopenia, neutropenia, thrombocytopenia, or pancytopenia.
From the label: adverse reactions, continuedTo report SUSPECTED ADVERSE REACTIONS, contact Waylis Therapeutics LLC Toll-Free at 1-888-514-4727 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. Hematologic The most common side effect is bone marrow suppression, anemia, leukopenia, neutropenia, thrombocytopenia, or pancytopenia. Although bone marrow suppression frequently occurs, it is usually reversible if the chlorambucil is withdrawn early enough. However, irreversible bone marrow failure has been reported. Gastrointestinal Gastrointestinal disturbances such as nausea and vomiting, diarrhea, and oral ulceration occur infrequently. CNS Tremors, muscular twitching, myoclonia, confusion, agitation, ataxia, flaccid paresis, and hallucinations have been reported as rare adverse experiences to chlorambucil which resolve upon discontinuation of drug. Rare, focal and/or generalized seizures have been reported to occur in both children and adults at both therapeutic daily doses and pulse-dosing regimens, and in acute overdose (see PRECAUTIONS: General). Dermatologic Allergic reactions such as urticaria and angioneurotic edema have been reported following initial or subsequent dosing. Skin hypersensitivity (including rare reports of skin rash progressing to erythema multiforme, toxic epidermal necrolysis, and Stevens-Johnson syndrome) has been reported (see WARNINGS). …
Source: FDA drug label, Waylis Therapeutics LLC, effective January 8, 2025 (SPL set 58a3c995-5ad6-465d-8437-5970c9088213), via openFDA; the full label on DailyMed
What do FAERS reports show?
3,917 reports list chlorambucil among the medicines taken, each a report of something that happened, not proof the medicine caused it; 925 are coded as a death and 1,625 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, 7 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.
Reports received each year
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?
- Chlorambucil: 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