Psyb65 human brain and behaviour: lectures 7 and 8. Non-commercial drugs (or available commercially but not for psychoactive effects) Tolerance: drug taken repeatedly reduced behavioural effect. Brain responds to compensate for repeated action of drug by changing sensitivity or number of receptors for drug. At normal level of activation, stimulant becomes less activated. At normal level of activating, depressant becomes hyperactivated. Coming off of a stimulant is not fatal, but off a depressant may cause seizures and may be fatal. There is also the psychological effect of craving with withdrawal. Addiction: psychological addiction: behavioural dependence on drug difficult to define/measure. Doesn"t have to be a drug: physical addiction: physiologically measurable symptoms. Stimulants: cause the eeg to move into a more activated state. Inhibits sleep: some tolerance develops, stops headaches, stimulates digestive system, withdrawal symptoms: (opposite of drug"s symptoms) headaches, constipation, not very toxic; estimated overdose = 70-100 cups of coffee needed to kill you.