Heroin is a drug. It is also known as Diacetylmorphine or Diamorphine. Heroin was originally a trade name. It is an opioid - a type of drug which acts like morphine in the body. Heroin is called a semi-synthetic opioid. This means it is made from an opiate that occurs in nature. For Heroin, that natural opiate is morphine.
Heroin is a white or brown powder made from the sap of the poppy plant. It is a painkiller. A painkiller is an analgesic drug. Its effects are like other drugs that come from the poppy plant sap. These include opium and morphine.
People smoke or inject heroin to get a calm feeling of relaxation. It is called "being high". The extreme happiness is known as euphoria. Heroin is a very addictive drug. This means that once a person starts taking heroin, they will want to take more and more. They will want to continue even when they know it is making them sick and harming them. Heroin is an illegal drug in many countries, unless it is used to treat a medical problem.
Drugs like cocaine, marijuana, and heroin have been decriminalized in numerous countries. To date, these include somewhere between 25 and 30 countries.