Drug abuse, i.e. Taking drugs excessively or not under a doctor's prescription, has become very serious in many countries. Drugs can be classified under several categories, and the same drug may fall into more than one category. For example, alcohol can be socially accepted drug and it can also be abused. For convenience, drugs can be classified as following: 1. Stimulant drugs: These drugs stimulate the central nervous system, e.g. Cocaine and amphetamines. Amphetamines are used to counteract depression, prevent fatigue and counteract hunger in patients who are dieting. 2. Depressant drugs: E.g. Barbiturates which are used as sleeping pills. These are prescribed to overcome insomnia and treat epilepsy. 3. Hallucinogenic drugs: E.g. Cannabis, also called marijuana and LSD (lysergic acid diethylamide). They cause the person to experience illusions, hallucinations and distorted images. 4. Opiates: E.g. Opium, morphine and heroin. These are narcotic drugs because they relieve pain and induce sleep and stupor. Heroin abuse is one of the biggest addiction problems in many countries around the world. Heroin is several times more powerful than morphine. Initially it dulls the senses, giving a sense of well-being. It reduces hunger, relieves tension and makes the user sleepy. These results do contribute to the large usage of heroine around the world.