Heroin is an illegal and highly addictive drug. It is the most abused and also the fastest acting of the opiates. Heroin is taken from morphine, a natural substance extracted from certain varieties of poppy plants. It is often sold as a white or brownish powder or as the black substance known on the streets as "black tar heroin." Most street heroin is "cut" with other drugs or with substances such as sugar, powdered milk, or quinine. Heroin on the street also can be cut with strychnine or other poisons. Because heroin abusers do not know the actual strength of the drug or its true contents, they are often at risk of overdose or death. Heroin also poses special problems because of the transmission of HIV and other diseases that can occur from sharing needles or other injection equipment.

Heroin is usually injected, sniffed/snorted, or smoked. Typically, a heroin abuser may inject up to four times a day or more. Intravenous injection provides the most intense "high" and the most rapid onset of euphoria (in as little as 7 to 8 seconds), while intramuscular injection produces a relatively slow onset of euphoria (5 to 8 minutes). When heroin is sniffed or smoked, peak effects are usually felt within 10 to 15 minutes. Researchers have confirmed that all forms of heroin administration are highly addictive.

Source: National Institute on Drug Abuse