Also known as marijuana, blow, dope, puff, grass, hash, wacky baccy, spliff, skunk.

Cannabis is the most widely used illicit drug in the UK. The supply and possession of cannabis is illegal in the UK and is likely to remain so for the foreseeable future. Cannabis was downgraded from a Class B drug to a Class C drug in January 2004. Supplying the drug carries the risk of a prison sentence of up to fourteen years, whilst possession for any reason could result in a two-year sentence. Similarly, growing cannabis at home for your own use could also lead to a prison sentence. In practice, the police often just issue a caution to people caught in possession of the drug, and it is possible that only persistent offenders are likely to find themselves in court.

Cannabis comes in two forms: cannabis resin (hashish) and marijuana, the dried leaves of Cannabis sativa. Cannabis is sold as blocks of compressed resin by the eighth or quarter of an ounce; marijuana is sold as dried leaves. Marijuana, or grass as it is generally known, varies in strength; a variety called `skunk' is now widely available in the UK. It has much stronger amounts of THC, the active ingredient which causes the hallucinogenic properties, than other forms of grass.

Cannabis can be smoked, usually with tobacco, eaten, drunk as a tea or snorted as a snuff. The drug affects the central nervous system, and as a result, users may experience relief from pain, feel light-headed, relaxed, or sleepy. The drug can also stimulate appetite; the so-called 'munchies'. In 1996, a clinical trial in San Francisco found that people with HIV wasting disease who used cannabis were more likely to put on weight. The drug is also widely used to relieve insomnia and the symptoms of anxiety and stress. It is also used by people with multiple sclerosis as a muscle relaxant. However, cannabis is also known to impair co-ordination, can cause nausea and vomiting, as well as anxiety and paranoia, which in long-term use may become chronic.

The effects of cannabis tend to depend on the pre–existing mood of the user, the amount used and the situation in which it is used. The most common, and also the most sought–after effects, are talkativeness, cheerfulness, relaxation and greater appreciation of sound and colour. Cannabis reduces individuals' abilities to do complicated tasks and can affect the short–term memory.

Because people can't concentrate as well, it is dangerous to drive or work machinery soon after using the drug. A driver under the influence of cannabis may be just as much of a danger as a driver under the influence of alcohol.

Chronic loss of memory and shortened attention span have been observed in long-term users of the drug, in some cases even after they have ceased, and there is evidence that long-term users can develop psychological dependency on the drug. Chronic use of cannabis has also been associated with the onset or long-term worsening of certain mental illnesses, most notably depression and psychosis and there is growing evidence of a link particularly in young people who start smoking strong forms of skunk at an early age.

Smoking cannabis is likely to harm an unborn child in just the same way as smoking tobacco, but there is no evidence that it exaggerates these effects.

Medical marijuana

Cannabis has been widely promoted as a medication in its own right, particularly as an appetite stimulant and as pain relief, and cases of elderly patients with conditions such as multiple sclerosis arrested for growing or possessing cannabis have occasionally hit the headlines. It has been used informally by people with HIV for the same reasons since the beginning of the epidemic and in San Francisco a ‘medical marijuana’ dispensary was operated by AIDS-dissident group ACT-UP SF.

To assess the extent of cannabis use, researchers from the Chelsea and Westminster Hospital asked patients attending the hospital’s HIV clinic to complete an anonymous questionnaire about their use of cannabis and the effects of the drug on their HIV-related symptoms.

“Despite the fact that cannabis is still illegal, its use for medical purposes appears to be quite widespread,” they write. “A large number of patients reported that cannabis improved symptom control.”

In total, 523 patients completed the questionnaire. Of these, 143 (27%) reported ever using cannabis to improve their symptoms. The majority (71%) only smoked cannabis, with 2% eating and drinking it and the rest combining eating, drinking and smoking the drug. Most patients (55%) took cannabis daily.

When asked why they took cannabis, 54% of the patients replied "to treat symptoms,” and 20% using it to “reduce symptom frequency.” Sixty-six per cent used cannabis to “relieve anxiety” and 52% to “relieve depression.”

However, 85% said that they used cannabis to “aid relaxation” and 43% “for a high.” It is not clear from the study to what extent these proportions overlapped.

Patients using cannabis reported significant improvements in symptoms. The greatest improvement was seen in appetite. Seventy-eight percent of the cannabis users reported a lack of appetite, but 97% of these experienced an improvement after using the drug (p < 0.001).

Forty-five per cent of the cannabis users reported pain, but the drug improved this in 94%. This included muscle pain (94%), nerve pain (90%), tingling (85%) and headache (65%).

Statistically significant improvements were also reported for nausea (93%), anxiety (93%) and depression (86%), as well as numbness (72%), weight loss (69%), tremor (66%), constipation (50%), tiredness (40%) and diarrhoea (36%).

However, 47% of the cannabis users reported memory loss after taking the drug (p = 0.043).

Cannabis and mental health

Cannabis, however, has also been associated with the development of psychosis, especially in young users, leading to demands that the drug be re-classified.

A longitudinal New Zealand study (Arseneault) which followed 1,000 people born in 1977 for 25 years found that young people who had started using cannabis by the age of 15 were 4.5 times as likely to develop schizophrenia in adulthood, while people who were heavy cannabis users before the age of 18 were six times more likely.