What is a generic medicine?

The regulatory definition

The FDA defines a generic drug as "a medication created to be the same as an already marketed brand-name drug in dosage form, safety, strength, route of administration, quality, and performance characteristics." The EMA uses a parallel concept: a generic medicine contains the same active substance in the same quantity as a reference medicine already authorised in the EU, in the same pharmaceutical form.

The key word in both definitions is same — applied to the active substance, not to the whole product. Inactive ingredients (colourants, fillers, binders), the tablet's shape and its trade name can legally differ, because patents and trademarks protect appearance and branding long after the molecule itself has come off patent.

Bioequivalence: what must actually be proven

The core requirement is bioequivalence. In a study on healthy volunteers, the generic and the reference product are compared on how much active substance reaches the bloodstream (AUC) and how quickly it peaks (Cmax). The 90% confidence interval for the ratio between the two products must fall within 80–125% for these parameters.

For some categories, bioequivalence studies in volunteers are unnecessary or impossible, and other evidence is used instead: in-vitro dissolution comparisons for certain oral forms, or comparative clinical endpoints for topical products. For narrow-therapeutic-index drugs (warfarin, levothyroxine, some antiepileptics) regulators apply tighter criteria.

The same factory rules apply

Approval is not only about the dossier. The manufacturing site must comply with Good Manufacturing Practice (GMP) and is subject to inspection by the regulator — regardless of which country it sits in. Both the FDA and EU authorities inspect overseas plants and have repeatedly suspended imports from facilities that failed.

This is why the useful question is never “generic or brand?” but “approved by a regulator I can verify, or not?” A great deal of the world's brand-name medicine and its generics are made in the same handful of countries, sometimes on the same industrial campus.

How to check a specific product yourself

1. For U.S. products: search the FDA Orange Book by active ingredient. It lists approved products and their therapeutic-equivalence codes.
2. A code beginning with A (for example AB) means the FDA considers the product therapeutically equivalent to the reference and substitutable for it. A B code means it is not.
3. For EU products: search the EMA medicine database, or your national agency's register for nationally authorised medicines.
4. Compare the active substance and strength on the box you were given against the prescription. The brand name may differ; the molecule and the strength must not.