Psychoactive substances obtained from Cannabis sativa or Indian hemp are the oldest euphoriants. Also called marijuana, these substances do not usually result in physical DEPENDENCE, but chronic abuse leads to passivity, apathy and inertia. Acute adverse effects include transient panic reactions and toxic psychoses. The panic reactions are characterised by anxiety, helplessness and loss of control and may be accompanied by florid paranoid thoughts and hallucinations. The toxic psychoses are characterised by the sudden onset of confusion and visual hallucinations. Even at lower doses, cannabis products can precipitate functional psychoses in vulnerable individuals. The acute physical manifestations of short-term cannabis abuse are conjunctival suffusion and tachycardia. In recent years, the circulation of particularly potent cannabis has been associated with an increasing prevalence of psychotic illness in users.

The chopped leaves are usually smoked but can be eaten in food or taken as tea. There is much public debate in Western countries over the social use of cannabis: it is illegal to possess or supply the substance in the United Kingdom, but nevertheless cannabis is quite widely used. Cannabis is not officially used medicinally, except in those US states which have legalised its sale, despite claims that it is helpful in ameliorating painful symptoms in certain serious chronic diseases such as multiple sclerosis. A related agent, NABILONE, is a synthetic cannabinoid licensed for use in treating nausea and vomiting caused by CYTOTOXIC drugs.