What the label lists and what reports show
Belimumab side effects
Belimumab's FDA label: “The most common serious adverse events were serious infections (6% and 5.2% in the groups receiving BENLYSTA and placebo plus standard therapy, respectively), some of which were fatal.” FAERS holds 31,474 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 (2,068 reports).
- No generic listed
Check it at the source: the belimumab FDA label on DailyMed (effective August 21, 2026); 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 BENLYSTA?BENLYSTA can cause serious side effects, including: See “What is the most important information I should know about BENLYSTA?” • Progressive multifocal leukoencephalopathy (PML). PML is a serious and life-threatening brain infection. Your chance of getting PML may be higher if you are treated with medicines that weaken your immune system, including BENLYSTA. PML can result in death or severe disability. If you notice any new or worsening medical problems such as those below, tell your healthcare provider right away: o memory loss o trouble thinking o dizziness or loss of balance o difficulty talking or walking o loss of vision • Cancer. BENLYSTA may reduce the activity of your immune system. Medicines that affect the immune system may increase your risk of certain cancers. […]
Source: FDA drug label, GlaxoSmithKline LLC, effective August 21, 2026 (SPL set 2fa3c528-1777-4628-8a55-a69dae2381a3), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common serious adverse events were serious infections (6% and 5.2% in the groups receiving BENLYSTA and placebo plus standard therapy, respectively), some of which were fatal.
Table 2. Incidence of Adverse Reactions Occurring in at Least 3% of Adult Subjects with Active SLE Treated with BENLYSTA 10 mg/kg plus Standard Therapy and at Least 1% More Frequently than in Subjects Receiving Placebo…
| Adverse Reactions | BENLYSTA 10 mg/kg + Standard Therapy (n = 674) % | Placebo + Standard Therapy (n = 675) % |
|---|---|---|
| Nausea | 15 | 12 |
| Diarrhea | 12 | 9 |
| Pyrexia | 10 | 8 |
| Nasopharyngitis | 9 | 7 |
| Bronchitis | 9 | 5 |
| Insomnia | 7 | 5 |
| Pain in extremity | 6 | 4 |
| Depression | 5 | 4 |
| Migraine | 5 | 4 |
| Pharyngitis | 5 | 3 |
| Cystitis | 4 | 3 |
| Leukopenia | 4 | 2 |
| Gastroenteritis viral | 3 | 1 |
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 are described below and in the Warnings and Precautions section: • Serious Infections [see Warnings and Precautions ( 5.1 )] • Hypersensitivity Reactions, including Anaphylaxis [see Warnings and Precautions ( 5.2 )] • Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis [see Warnings and Precautions ( 5.3 )] • Depression and Suicidality [see Warnings and Precautions ( 5.4 )] • Malignancy [see Warnings and Precautions ( 5.5 )] Common adverse reactions (≥5%): nausea, diarrhea, pyrexia, nasopharyngitis, bronchitis, insomnia, pain in extremity, depression, migraine, pharyngitis, and injection site reactions (subcutaneous administration). ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact GlaxoSmithKline at 1-877-423-6597 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 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 with rates in the clinical trials of another drug and may not reflect the rates observed in practice. …
Source: FDA drug label, GlaxoSmithKline LLC, effective August 21, 2026 (SPL set 2fa3c528-1777-4628-8a55-a69dae2381a3), via openFDA; the full label on DailyMed
What do FAERS reports show?
31,474 reports list belimumab among the medicines taken, each a report of something that happened, not proof the medicine caused it; 893 are coded as a death and 4,627 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 17 reactions below, 9 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?
- Belimumab: 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