What the label lists and what reports show
Interferon beta 1b side effects
Interferon beta 1b's FDA label: “In controlled clinical trials, the most common adverse reactions (at least 5% more frequent on BETASERON than on placebo) were: injection site reaction, lymphopenia, flu-like symptoms, myalgia, leukopenia, neutropenia, increased liver enzymes, headache …” FAERS holds 19,060 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 influenza like illness (1,402 reports).
- No generic listed
Check it at the source: the interferon beta 1b FDA label on DailyMed (effective March 3, 2026, Bayer HealthCare Pharmaceuticals 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 BETASERON?BETASERON may cause serious side effects. Call your healthcare provider right away if you have any of the serious side effects of BETASERON including: • See "What is the most important information I should know about BETASERON?" • heart problems. BETASERON may worsen heart problems including congestive heart failure. Symptoms of heart problems may include: • swollen ankles • shortness of breath • not being able to lay flat in bed • tightness in chest • decreased ability to exercise • fast heartbeat • increased need to urinate at night • injection site problems. Serious skin reactions can happen in some people including areas of severe damage to skin and the tissue below the skin (necrosis). These reactions can happen anywhere you inject BETASERON. […]
Source: FDA drug label, Bayer HealthCare Pharmaceuticals Inc., effective March 3, 2026 (SPL set 66311f74-0472-4fa3-848a-06002ca0def5), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsIn controlled clinical trials, the most common adverse reactions (at least 5% more frequent on BETASERON than on placebo) were: injection site reaction, lymphopenia, flu-like symptoms, myalgia, leukopenia, neutropenia, increased liver enzymes, headache, hypertonia, pain, rash, insomnia, abdominal pain, and asthenia.
Table 2: Adverse Reactions and Laboratory Abnormalities in Patients with MS in Pooled Studies 1, 2, 3, and 4
| Adverse Reaction | Placebo (N=965) | BETASERON (N=1407) |
|---|---|---|
| Lymphocytes count decreased (<1500/mm3) | 66% | 86% |
| Absolute neutrophil count decreased (<1500/mm3) | 5% | 13% |
| White blood cell count decreased (<3000/mm3) | 4% | 13% |
| Lymphadenopathy | 3% | 6% |
| Headache | 43% | 50% |
| Insomnia | 16% | 21% |
| Incoordination | 15% | 17% |
| Hypertension | 4% | 6% |
| Dyspnea | 3% | 6% |
| Abdominal pain | 11% | 16% |
| Alanine aminotransferase increased (SGPT > 5 times baseline) | 4% | 12% |
| Aspartate aminotransferase increased (SGOT > 5 times baseline) | 1% | 4% |
| Rash | 15% | 21% |
| Skin disorder | 8% | 10% |
| Hypertonia | 33% | 40% |
| Myalgia | 14% | 23% |
| Urinary urgency | 8% | 11% |
| Metrorrhagia | 7% | 9% |
| Impotence | 6% | 8% |
| Injection site reaction "Injection site reaction" comprises all adverse reactions… | 26% | 78% |
| Asthenia | 48% | 53% |
| Flu-like symptoms (complex) "Flu-like symptom (complex)" denotes flu syndrome and/or a… | 37% | 57% |
| Pain | 35% | 42% |
| Fever | 19% | 31% |
| Chills | 9% | 21% |
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 discussed in more details in other sections of labeling: • Hepatic Injury [see Warnings and Precautions ( 5.1 )] • Anaphylaxis and Other Allergic Reactions [see Warnings and Precautions ( 5.2 )] • Depression and Suicide [see Warnings and Precautions ( 5.3 )] • Congestive Heart Failure [see Warnings and Precautions ( 5.4 )] • Injection Site Reactions Including Necrosis [see Warnings and Precautions ( 5.5 )] • Leukopenia [see Warnings and Precautions ( 5.6 )] • Thrombotic Microangiopathy [see Warnings and Precautions ( 5.7 )] • Pulmonary Arterial Hypertension [see Warnings and Precautions ( 5.8 )] • Flu-like Symptom Complex [see Warnings and Precautions ( 5.9 )] • Seizures [see Warnings and Precautions ( 5.10 )] • Drug Induced Lupus Erythematosus [see Warnings and Precautions ( 5.11 )] In controlled clinical trials, the most common adverse reactions (at least 5% more frequent on BETASERON than on placebo) were: injection site reaction, lymphopenia, flu-like symptoms, myalgia, leukopenia, neutropenia, increased liver enzymes, headache, hypertonia, pain, rash, insomnia, abdominal pain, and asthenia.
Source: FDA drug label, Bayer HealthCare Pharmaceuticals Inc., effective March 3, 2026 (SPL set 66311f74-0472-4fa3-848a-06002ca0def5), via openFDA; the full label on DailyMed
What do FAERS reports show?
19,060 reports list interferon beta 1b among the medicines taken, each a report of something that happened, not proof the medicine caused it; 1,337 are coded as a death and 4,226 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. Reports rose sharply in 2016 (1,393, against a median of 400 a year): FAERS counts follow reporting, which news, litigation and label changes can drive, not how often a reaction happens. Of the 21 reactions below, 10 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?
- Interferon beta 1b: 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