Heroin officially referred to as diamorphine or more properly as diacetylmorphine is a semi-synthetic opioid most commonly used for recreational purposes in the United States. Heroin still finds use in some other countries as treatment for acute and post-operative pain as well as palliative therapy for the terminally ill.

Known by the street names as horse, smack, brown or junk, heroin has a half life in the body of about 30 minutes but may remain active for 4-5 hours. Depending of the route of administration it may provide users an intense rush or high with the onset as soon as several seconds after intravenous injection or smoking. Alternatively the rush or pleasurable sensation may be delayed for more than 10 minutes after sniffing the drug.

Associated with the initial rush many users note watery eyes, runny nose, warm flushed skin, severe itching, sweating and loss of appetite. After these initial effects of heroin, drowsiness lasts several hours with some describing a trance like state associated with head nodding due to the resulting sleepiness.

Of more concern, heroin may significantly slow the heart rate and lead to severe slowing of the respiratory rate. At times decreased breathing may lead to potentially irreversible brain damage.

In the body, heroin is converted to morphine. However unique to heroin is the metabolically active breakdown product – 6 monoacetylmorphine - which may be associated with the initial euphoria and preference of abusers for heroin rather than morphine.

Fear of infection and other consequences of heroin use limits the percent of users injecting heroin to about 45-50% - a number constant over the decades. Other routes of administration include smoking, snorting and either intramuscular or subcutaneous injections. Most heroin addicts also abuse other illicit drugs. Heroin may even be purchased in pill form. The majority of heroin sold in America originates in Mexico or Colombia.