Heroin is a semi-synthetic opiate. It is derived from the latex of the opium poppy, and it is a very powerful narcotic. In its pure form, it can be used as a painkiller and analgesic in medical situations. However, it is also a commonly-used and highly addictive street drug. The medical-grade version of heroin, called diamorphine, is commonly used in the United Kingdom rather than morphine as a painkiller after surgeries and major injuries. Heroin and all its derivatives are synthesized from the drug morphine, which itself is synthesized from the opium poppy.
Heroin depresses the part of the brain responsible for breath rate and heart rate, so it can easily cause an individual who has taken too much to slip into a coma. In addition, street heroin is often cut with other substances. As a result, taking street heroin is always a gamble, because you can never be sure how pure the drug is. If it is very pure and you take too much, you can overdose and die.