A generic drug is a pharmaceutical drug that contains the same chemical substance as a drug that was originally protected by chemical patents.. To facilitate generic drug product availability and to assist the generic pharmaceutical industry with identifying the most appropriate methodology for developing drugs and generating evidence needed to support ANDA approval, FDA regularly publishes product-specific guidances describing the Agency’s current thinking and expectations on how to develop therapeutic equivalents to specific reference listed drugs. When a pharmaceutical company first markets a drug, it is usually under a patent that, until it expires, the company can use to exclude competitors by suing them for patent infringement. Pharmaceutical companies that develop new drugs generally only invest in drug candidates with strong patent protection as a strategy to recoup their costs of drug development (including the costs of the drug candidates that fail) and to make a profit.