Cannabis can be smoked, usually with tobacco, eaten, drunk in 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’. However, cannabis is also known to impair co-ordination, can cause nausea and vomiting, as well as emotional and mental health problems such as anxiety and paranoia, which in long-term use may become chronic.

The supply and possession of cannabis is illegal in the UK. It is currently a 'Class B' drug.

Conviction for supplying cannabis can result in a lengthy prison sentence and a large fine. Similarly, growing cannabis at home for your own use could also lead to a prison sentence. The current maximum sentence for possession of cannabis is five years in prison.

Medicinal use of cannabis is illegal and therefore there is little verifiable evidence of the drug’s effects when used in the management of chronic health conditions. However, cannabis is widely used by people for medicinal reasons, often for the relief of pain, or as an appetite stimulant. 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. A study in 2007 found that HIV-positive users of the drug had relief from the symptoms of peripheral neuropathy. 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.

A small number of people have been prosecuted for growing and consuming cannabis for medicinal purposes.

Cannabis extracts, called cannabinoids, are already legally used in licensed pharmaceuticals, mostly pain killers and muscle relaxants, but these can only be obtained on prescription. These products do not make users feel ‘high’ or have any of the other narcotic effects of cannabis.

Short-term risks of cannabis use include anxiety, panic, and paranoia. Memory and attention may also be affected, as might the ability to drive or operate machinery. Research suggests that cannabis use in teenagers is a predictor of later mental health problems. Use during pregnancy has been associated with low birth-weight babies.

If the drug is smoked, long-term use is known to cause many smoking-related respiratory and cardiovascular diseases such as asthma, bronchitis, emphysema and heart disease. This may be of particular concern to people with HIV who have suffered lung damage from lung infections, or to those with increased lipids as this may increase the risk of heart attack.

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. In one survey, daily use of cannabis by teenagers was found to substantially increase the risk of developing depression later in life and the use of cannabis has also been linked with an increased risk of schizophrenia.

One study found that use of cannabis was associated with more severe liver damage in patients with hepatitis C.

It is not known how cannabis reacts with anti-HIV drugs. A small American study found that cannabis use did not impact on the effectiveness of the protease inhibitor indinavir (Crixivan) even though the drugs use the same mechanism to pass through the body. Like any mood and consciousness-altering drug, cannabis may have an impact on people’s ability to adhere to their medication schedule and people planning to use cannabis, or any other recreational drug, may need to develop strategies to help them take their medication at the right time and in the right way.

NAM reminds readers that cannabis use is illegal in the UK. This factsheet has been produced with UK law in mind. Readers in other countries should be aware that the legal status of cannabis use may differ to that which is described in this factsheet.