Randomized clinical trials are often conducted in selected target populations, where the sample sizes are small and the treatment duration is short; therefore, rare events and adverse events with long lag periods are not fully characterized, and safety in the wider general population is unknown. Following the tragedies related to congenital abnormalities with the use of Thalidomide, regulations in general and national pharmacovigilance centers were set up to follow up drugs once they were authorized and marketed. The most frequently associated risks with biopharmaceuticals are attributable to their immune-modulatory actions. At the time of authorization of a biosimilar drug product, a reduced nonclinical and clinical data package is acceptable if similarity between the reference product and the biosimilar product is clearly demonstrated. Another challenge in the pharmacovigilance of subsequent-entry biologics (SEBs) is interchangeability. The introduction of biosimilars also poses a challenge for naming and tracking adverse events associated with the biosimilar and innovator product.