What the label lists and what reports show
Rilonacept side effects
Rilonacept's FDA label: “The most common adverse reactions reported by patients with CAPS and RP treated with ARCALYST are injection-site reactions and upper respiratory tract infections.” FAERS holds 1,121 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 injection site erythema (132 reports).
- No generic listed
Check it at the source: the rilonacept FDA label on DailyMed (effective December 16, 2025); 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 ARCALYST?ARCALYST can cause serious side effects, including: See " What is the most important information I should know about ARCALYST? " Risk of Cancer. Medicines that affect the immune system may increase the risk of getting cancer. Allergic Reaction. Stop taking or giving ARCALYST and call the healthcare provider or get emergency care right away if you or your child get any of the following symptoms of an allergic reaction while taking ARCALYST: rash swollen face trouble breathing Changes in your blood cholesterol and triglycerides (lipids). Your or your child's healthcare provider will do blood tests to check for these changes. In people with CAPS and RP, the most common side effects of ARCALYST include: Injection-site reactions including: pain, redness, swelling, itching, bruising, lumps, inflammation, skin rash, blisters, warmth, and bleeding at the injection site. […]
Source: FDA drug label, Kiniksa Pharmaceuticals (UK), Ltd., effective December 16, 2025 (SPL set ad965f38-dd22-4607-a673-2fb92f3b527a), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common adverse reactions reported by patients with CAPS and RP treated with ARCALYST are injection-site reactions and upper respiratory tract infections.
Table 1: Most Frequent Adverse Reactions in Patients with CAPS (Part A, Reported by at Least Two Patients)
| Adverse Event | ARCALYST 160 mg (n = 23) | Placebo (n= 24) |
|---|---|---|
| Any AE | 17 (74%) | 13 (54%) |
| Injection-site reactions | 11 (48%) | 3 (13%) |
| Upper respiratory tract infection | 6 (26%) | 1 (4%) |
| Nausea | 1 (4%) | 3 (13%) |
| Diarrhea | 1 (4%) | 3 (13%) |
| Sinusitis | 2 (9%) | 1 (4%) |
| Abdominal pain upper | 0 | 2 (8%) |
| Cough | 2 (9%) | 0 |
| Hypoesthesia | 2 (9%) | 0 |
| Stomach discomfort | 1 (4%) | 1 (4%) |
| Urinary tract infection | 1 (4%) | 1 (4%) |
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 clinically significant adverse reactions are described elsewhere in the labeling. Serious Infections [see Warnings and Precautions (5.1) ] Risk of Malignancy [see Warnings and Precautions (5.2) ] Hypersensitivity Reactions [see Warnings and Precautions (5.3) ] Lipid Profile Changes [see Warnings and Precautions (5.4) ] The most common adverse reactions reported by patients with CAPS and RP treated with ARCALYST are injection-site reactions and upper respiratory tract infections. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Kiniksa at 1-833-KINIKSA (1-833-546-4572) or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trial Experience Clinical trials are conducted under widely varying conditions and, as such, adverse reaction rates observed cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice. The data described herein reflect exposure to ARCALYST in over 2,000 patients who received at least one dose, including approximately 1700 exposed to 160 mg or more, of whom 151 patients were exposed for at least 6 months and 111 patients for at least one year. These included patients with CAPS and RP, patients with other diseases, and healthy volunteers. CAPS Approximately 60 patients with CAPS were treated weekly with 160 mg of ARCALYST. …
Source: FDA drug label, Kiniksa Pharmaceuticals (UK), Ltd., effective December 16, 2025 (SPL set ad965f38-dd22-4607-a673-2fb92f3b527a), via openFDA; the full label on DailyMed
What do FAERS reports show?
1,121 reports list rilonacept among the medicines taken, each a report of something that happened, not proof the medicine caused it; 24 are coded as a death and 122 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 19 reactions below, 3 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?
- Rilonacept: 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