Heroin (diacetylmorphine or morphine diacetate, also known as diamorphine (BAN)) and commonly known by its street names of H, smack, horse, brown, black, tar, and others, is an opioid analgesic originally synthesized by C.R. Alder Wright in 1874 by adding two acetyl groups to the molecule morphine, which is found naturally in the opium poppy. It is the 3,6-diacetyl ester of morphine. Heroin itself is an inactive drug, but when inserted into the body, it converts into morphine. Heroin is the most addictive drug, and there is practically no chance of getting clean from it. It's also a very dangerous drug.
Illicit heroin is sometimes available in freebase form, dulling the sheen and consistency to a matte-white powder. Because of its lower boiling point, the freebase form of heroin is also smokable. It is prevalent in heroin coming from Afghanistan, which as of 2004 produced roughly 87% of the world supply in illicit raw opium. However, the production rate in Mexico has risen sixfold from 2007 to 2011, changing that percentage and placing Mexico as the second largest opium producer in the world.
As with other opioids, diacetylmorphine is used as both an analgesic and a recreational drug. Frequent and regular administration is associated with tolerance and physical dependence. Internationally, diacetylmorphine 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 almost every country, except the UK and Switzerland.
It is also available for prescription to long-term users as a form of opioid replacement therapy in the United Kingdom, Netherlands, Switzerland, Germany, and Denmark, alongside psycho-social care—in the same manner that methadone or buprenorphine are used in the United States and Canada—and a similar program is being campaigned for by liberal political parties in Norway.