Drugs are beneficial to mankind when used properly under strict medical advice but some drugs are harmful when misused or used excessively for non-medical purposes. The drugs whose misuse can be harmful are classified into the following four categories :
(i) Narcotics : Drugs under this category produce drowsiness, sleep and numbing effect on muscles. Nevocaine, Codeine and Morphine are the main drugs of this group. Nevocaine is used by dentists as local anaesthesia (pain killer) for tooth extraction purposes. Morphine is also used as pain killer in cases of severe or unbearable pain. Codeine is generally used in cough syrups. These medicines,when misused, can lead to addiction and can also be fatal in excessive doses.
(ii) Depressants/Sedatives : These are used for muscular relaxation and to reduce tension resulting from anxiety. This group contains Bromides and Barbiturates. Barbiturate groups of sedative drugs are derived from barbituric acid which is a combination of malonic acid and urea. These medicines can lead to coma or even death when taken in large doses.
(iii) Stimulants : Such drugs cause excitement and result in the loss of sleep. The excitement is for a short time with the accompanying loss of appetite. In this, category come Amphetamines. Medically these are used in depression. When taken regularly, they can lead to addiction.
(iv) Hallucinogens : Various forms of Hallucinogens are L.S.D., Heroin, "Ganja", etc. Such drugs cause hallucinations or illusions because these drugs influence one's mental and visual faculties.