heroin A semisynthetic drug derived from, but more potent than, morphine. Heroin is now better known as a drug of abuse than for its medical uses. Heroin may be injected into a vein, injected under the skin, snorted, or smoked. It is highly addictive, and overdose is an ever-present possibility due to the varying purity of street drugs. Treatment of heroin addiction may involve the use of medications such as methadone, a synthetic opoid, and buprenorphine.