Cannabis has a mildly sedative effect, which leads to decreased blood pressure, increased appetite, feelings of relaxation, mild intoxication and increased sociability. People who smoke the drug usually feel its effects within minutes and they may last up to three hours.

The effect is delayed when eating or drinking the drug so that it lasts longer and may be more difficult to control. Cannabis may impair short-term memory and affects body coordination. First-time users may feel confused and distressed and anxiety, panic and suspicion are not uncommon side effects. High doses can cause coma, but there are no records of fatal overdose. Heavy use can lead to confusion, aggravate existing mental disorders and sap energy. Some people believe cannabis can lead to hard drug use, such as heroin, but the majority of users do not go on to take heroin.

Long-term use of cannabis can cause lung cancer, bronchitis and other respiratory disorders associated with smoking. It is unclear if there is more risk of these disorders than with tobacco. However, cannabis users tend to inhale more deeply and the drug does contain higher doses of tar. People may become psychologically dependant on cannabis. Some research also suggests that physical addiction is possible, although this is hotly disputed.

But there is evidence that cannabis can relieve the symptoms of some chronic conditions, such as multiple sclerosis.