Biosimilars in Modern Therapeutics: Science, Regulation, and the Economics of Biological Copies

The expiry of patents covering the first generation of recombinant biological medicines has opened the way for a distinct class of therapeutics known as biosimilars — biological products developed to be highly similar, though never identical, to an already-licensed reference biologic. Unlike small-molecule generic drugs, which can be reproduced as exact chemical copies, biosimilars are manufactured in living cells through processes that are inherently variable, so that perfect replication of the reference product is not achievable. This review draws together historical, regulatory, clinical, and economic literature, together with current regulatory and market data, to give an integrated picture of where the field now stands. It traces the conceptual distinction between biosimilars, generics, and originator biologics; examines the manufacturing and analytical challenges that make biosimilar development a fundamentally different exercise from generic drug development; and compares the regulatory pathways of the European Medicines Agency, the United States Food and Drug Administration, and the World Health Organization, including the substantial policy shifts of 2022–2025 toward routine interchangeability. The review also considers immunogenicity, extrapolation of indications, switching, and interchangeability, and the economic forces that have shaped biosimilar uptake in Europe and the United States, where generic and biosimilar medicines together generated an estimated 467 billion United States dollars in healthcare savings in 2024 alone. Evidence from erythropoietin, filgrastim, infliximab, etanercept, and adalimumab biosimilars illustrates general principles throughout. The review concludes that, while biosimilars carry genuine promise for expanding access to biological therapy and easing the financial burden on health systems, their responsible use depends on continued vigilance around manufacturing consistency, robust post-marketing surveillance, and clear communication between regulators, manufacturers, and clinicians.