An intravenous drug (IV drug) is a drug administered intravenously, either by an intravenous drip or a syringe. As it is one of the most effective methods of administering drugs with rapid effect, it is used widely used in medical practice and by recreational drug users.

The reuse of syringes to administer drugs intravenously is a primary vector for diseases that can be transmitted through blood, and the practice is expressly forbidden in medicine. However, such reuse, known colloquially as needle sharing, is common among users of illegal drugs. Because these diseases include fatal venereal diseases such as hepatitis and AIDS, illegal IV drug use has become a societal health threat, and programs to decrease needle sharing have been established, often in contravention of the law.