Nicotine has both negative and positive reinforcing effects. Relief of withdrawal symptoms is the most recognized negative reinforcer. Its reinforcing actions are thought to be related to the central stimulation of nicotinic cholinergic receptors which eventually lead to dopamine release. PCP use in humans occurs by intranasal, IV, oral or inhalation routes of administration. Peak plasma concentrations occur within 5-10 min after PCP is smoked.
Metabolism is primarily hepatic with renal secretion of hydroxylase metabolites.
PCP-like drugs possess reinforcing properties and are addictive drugs. Repeated administration of PCP leads to tolerance and dependence. All of the commonly used hallucinogens are readily absorbed by mouth. Biotransformation occurs in the liver by routes that differ for each drug.