Heroin, or diacetylmorphine (INN), also known as diamorphine (BAN), is a semi-synthetic opioid drug synthesized from morphine, a derivative of the opium poppy. It is the 3,6-diacetyl ester of morphine (di(two)-acetyl-morphine). The white crystalline form is commonly the hydrochloride salt diacetylmorphine hydrochloride, though often adulterated thus dulling the sheen and consistency from that to a matte white powder, which heroin freebase typically is.

As with other opioids, heroin is used as both a pain-killer and a recreational drug and has an extremely high potential for abuse. Frequent and regular administration is associated with tolerance, moderate physical dependence, and severe psychological dependence.

Internationally, heroin is controlled under Schedules I and IV of the Single Convention on Narcotic Drugs. It is illegal to manufacture, possess, or sell diacetylmorphine without a license in Belgium, Denmark, Germany, Iran, India, the Netherlands, the United States, Australia, Canada, Ireland, Pakistan, the United Kingdom and Swaziland.

Under the name diamorphine, it is a legally prescribed controlled drug in the United Kingdom. It is available for prescription to long-term users in the Netherlands, United Kingdom, Switzerland, Germany and Denmark alongside psycho-social care, and a similar program is being campaigned for by liberal political parties in Norway. (Via Wikipedia)