Generic medicines (or equivalent drugs) are medicines that contain the same active substance, the same dose and the same pharmaceutical form (tablets, drops, etc), as a registered trademark medicine. In Europe patents are valid for twenty years. When this period ends, the medicine may be produced and sold, without the trademark, but with the name of the main active substance.

This allows for savings of about 20% for both buyers and the National Health Service. Generic medicines may be OTC (buyable without medical prescription) or prescribable medicines (only with medical prescription).