A generic drug is an agent that is similar to a branded or reference-listed drug in terms of dosage, administration and performance. A generic drug is marketed when the original patent protection that was applied to the drug expires or when the owner of the patent waives its rights.
 

When a pharmaceutical company first develops a drug, it applies for a patent. This means that only the company that has developed the original molecule can manufacture and market the drug during its patent protection period. Once the patent protection expires after a fixed number of years, other pharmaceutical companies are also allowed to manufacture the drug. At this point, the drug is referred to as a generic drug. Due to the competitive nature of the drug market, once the generic drug is available, the cost of both the original branded product and the generic drug are significantly lowered.

As per the guidelines of the United States Food and Drug Administration (FDA), the generic drug must contain the same active ingredient as the branded drug as well as being identical in terms of the following:

• Pharmacokinetic properties
• Pharmacodynamic properties
• Mechanism of action
• Efficacy
• Safety
• Dosage
• Strength
• Intended usage
• Route of administration

This term identical is a legal term here rather than a literal term. In literal terms, “bioequivalence” is what is required between the generic and branded products. Bioequivalence between the two drugs means they share a similar bioavailability and give rise to the same effects at their site of action. All companies that intend to manufacture a generic drug must ensure that their product is bioequivalent to the original molecule in order to receive approval from the drug regulators.