Biologics are medicines made from living cells or organisms, such as bacteria, yeast, or animal cells. This differs from most conventional drugs, which are small chemicals synthesized in a laboratory.

They are usually large, complex proteins that act on a specific part of the immune system or another biological pathway. Examples include:

In everyday clinical use, “a biologic” often means a targeted immune-modifying treatment for conditions such as rheumatoid arthritis, psoriasis, inflammatory bowel disease, severe asthma, migraine, and some cancers. For example, adalimumab blocks TNF, an inflammatory signaling protein.

How they are given: Many would be digested if swallowed, so they are commonly administered by injection or intravenous infusion.

Benefits: They can be very effective and more targeted than broad immune suppressants.

Important risks: Depending on the drug, they can raise infection risk, cause infusion or injection reactions, or reactivate infections such as tuberculosis or hepatitis B. Screening and monitoring are often needed.

A biosimilar is a highly similar version of an already approved biologic. It is not an exact molecular copy, because biologics are produced by living systems, but it must have no clinically meaningful difference in safety or effectiveness from the reference product, as explained by the FDA biosimilar overview.

A biologic is the original medicine made using living cells or organisms. A biosimilar is a later-developed biologic designed to closely match an already approved original, called the reference product.

A generic tablet such as generic ibuprofen can contain the same active chemical molecule as the brand product. Biologics are much larger and are manufactured in living cells, so an exact duplicate cannot be made. Instead, manufacturers demonstrate that a biosimilar has matching critical structural and functional features and performs equivalently in clinical use. Rheumatology, 2-Volume Set, pp. 5931-5954.

In the United States, an interchangeable biosimilar meets additional FDA requirements. Depending on state pharmacy law, it may be substituted for the reference biologic at the pharmacy level without the prescriber authorizing each individual switch. A regular biosimilar is still FDA-approved as safe and effective for its authorized uses, but it does not necessarily have that pharmacy-substitution designation. The FDA explanation of biologic definitions describes this distinction.