Drug patents typically last 20 years. However, the effective patent life can be shorter due to the time required for drug development and FDA approval. During this period, the patent is in effect but the drug cannot be sold. Once on the market, drugs generate substantial revenue during the remainder of the patent period. When patents expire, generic competitors can enter the market, reducing prices but also the brand manufacturer's profits. Factors like regulatory review times can impact how long a drug has exclusive patent protection.