generic drug, a drug sold or prescribed under the nonproprietary name of its active ingredients or under a generally descriptive name rather than under a brand or trade name. The name of the active ingredient is established by a government or international body, and is typically the U.S. Adopted Name, British Approved Name, or International Nonproprietary Name. Generic drugs must contain the same active ingredients that their brand name counterparts do and are tested to assure that they are therapeutically equivalent, but they may contain different inactive ingredients from those found in the brand name medications.

There are generic versions of both over-the-counter and prescription medications, but not all drugs have generic equivalents. Generic drugs can only be produced when a patent on a brand name drug expires or when a patent has never existed. They are generally cheaper than the equivalent brand name drug because of much lower marketing and development costs. Because a generic competitor can hurt a brand name manufacturer's profits, drug companies have used legal action and regulatory delays to slow the introduction of generics, or have paid generic manufacturers to postpone the production and marketing of generics. The Medicare overhaul legislation passed in 2003 contained sections designed to speed the introduction of generic drugs by making it easier to challenge weak or invalid drug patents.