Drugs are habit forming substances. They react with the nervous system of the body and affecting the individual mentally and physically. Dependence of the body on drugs due to the prolonged use is known by the name drug addiction. Some diseases are cured by drugs , physicions prescribed drugs as a treatment. Some are used to prevent infection .some drugs are altering mood. Drugs can be inhaled or orally taken or taken by injection. Some drugs are leads to drug dependence , the patient totally dependent on them . the psychotropic drugs come under this category. These drugs are used as mood alters .they are also known as mood altering drugs. Psychedelic drugs give a state of relaxation and pleasure. Drugs are manly classified as four types they are sedatives, tranquilizers, opiate narcotics, stimulators etc. sedative and tranquilizers give a switching off feelings on the brain . in higher doses drugs induce sleep and in low doses may produce feeling of calmness. Barbiturates are come under this category. Opiate narcotic are usually used as pain killers , which consists of morphine , codeine, heroin, methadone etc . opiate narcotics reduce anxiety and tension , etc.