Orphan drugs are medications developed to treat rare diseases, which typically affect a small percentage of the population e.g. less than 200,000 in the US. The 1983 Orphan Drug Act is a piece of US legislation, mirrored in other jurisdictions designed to incentivise the development of orphan drugs. The Orphan Drug act provides large tax benefits and an additional 7 years of market exclusivity for Orphan Drugs.