In a typical year, approximately 20 percent of the prescriptions filled in the U.S. are of the psychoactive (mood - changing) variety : stimulants, including appetite suppressions, and depressants – ranging from sleep – inducing sedatives to minor tranquilizers are counted in this category. Another class of drugs in common use which may cause addiction are the analgesics (pain-killers). All these drugs act on the central nervous system. They are often over – prescribed and misused and lead to dependence. Prescriptions for mood-altering drugs are disproportionately high among women because they constitute the largest group of patients seeking medical advice.