What the label lists and what reports show
Cladribine side effects
Cladribine's FDA label: “Most common adverse reactions (incidence > 20%) are upper respiratory tract infection, headache, and lymphopenia.” FAERS holds 9,555 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 fatigue (814 reports).
- Generic listed
- Boxed warning
Check it at the source: the cladribine FDA label on DailyMed (effective May 27, 2026, EMD Serono, 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 MAVENCLAD?MAVENCLAD can cause serious side effects, including: See " What is the most important information I should know about MAVENCLAD? " low blood cell counts. Low blood cell counts have happened and can increase your risk of infections during your treatment with MAVENCLAD. Your healthcare provider will do blood tests before you start treatment with MAVENCLAD, during your treatment with MAVENCLAD, and afterward, as needed. serious infections such as: Infections caused by bacteria, viruses, parasites, or fungi that may be life-threatening or cause death. TB, hepatitis B or C, and shingles (herpes zoster). Fatal cases of TB and hepatitis have happened with cladribine during clinical studies. […]
Source: FDA drug label, EMD Serono, Inc., effective May 27, 2026 (SPL set 9c75e30a-a410-40f1-b653-04d532bd9144), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse reactions (incidence > 20%) are upper respiratory tract infection, headache, and lymphopenia.
Table 2 Adverse Reactions in Study 1 with an Incidence of at Least 5% for MAVENCLAD and Higher than Placebo
| Reaction | MAVENCLAD (N=440) % | Placebo (N=435) % |
|---|---|---|
| Upper respiratory tract infection | 38 | 32 |
| Headache | 25 | 19 |
| Lymphopenia | 24 | 2 |
| Nausea | 10 | 9 |
| Back pain | 8 | 6 |
| Arthralgia and arthritis | 7 | 5 |
| Insomnia | 6 | 4 |
| Bronchitis | 5 | 3 |
| Hypertension | 5 | 3 |
| Fever | 5 | 3 |
| Depression | 5 | 3 |
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 serious adverse reactions and potential risks are discussed, or discussed in greater detail, in other sections of the labeling: Malignancies [see Warnings and Precautions (5.1) ] Risk of Teratogenicity [see Warnings and Precautions (5.2) ] Lymphopenia [see Warnings and Precautions (5.3) ] Infections [see Warnings and Precautions (5.4) ] Hematologic Toxicity [see Warnings and Precautions (5.5) ] Graft-Versus-Host Disease With Blood Transfusion [see Warnings and Precautions (5.6) ] Liver Injury [see Warnings and Precautions (5.7) ] Hypersensitivity [see Warnings and Precautions (5.8) ] Cardiac Failure [see Warnings and Precautions (5.9) ] Most common adverse reactions (incidence > 20%) are upper respiratory tract infection, headache, and lymphopenia. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact EMD Serono at 1-800-283-8088 ext. 5563 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical studies 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 studies of another drug and may not reflect the rates observed in practice. In the clinical trial program of cladribine in MS, 1,976 patients received cladribine for a total of 9,509 patient years. …
Source: FDA drug label, EMD Serono, Inc., effective May 27, 2026 (SPL set 9c75e30a-a410-40f1-b653-04d532bd9144), via openFDA; the full label on DailyMed
What do FAERS reports show?
9,555 reports list cladribine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 709 are coded as a death and 2,213 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, 4 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?
- Cladribine: 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