Cannabis or marijuana is an illegal drug derived from the leaves and flowers of the cannabis plant. It is are smoked, eaten or drunk in tea. Cannabis can reduce pain symptoms, as well as causing relaxation, sleepiness and light-headedness.

In low doses, cannabis can reduce nausea and stimulate the appetite. However, it can also cause hallucinations, impaired co-ordination, nausea and vomiting, particularly in high doses. In the long-term, some users can become anxious or paranoid, or develop memory problems.

Patients with HIV often use cannabis as an appetite stimulant or to alleviate symptoms of pain. A survey of HIV-positive patients at a large London hospital found that 27% had used cannabis to alleviate symptoms, including reduced appetite, pain, nausea, anxiety and depression. However almost half of the cannabis users reported memory problems^[1]. Similar rates were seen in a study in Canada^[2]. However, a study in San Francisco found lower rates of cannabis use, but for similar reasons^[3].

In contrast to other drugs of abuse, cannabis use may not necessarily reduce adherence. Despite two studies finding a link between cannabis use and worse adherence, a recent study found that relief of moderate or severe nausea with cannabis led to better adherence to anti-HIV treatment^[4][5][6]. There is no evidence of a link between cannabis use and HIV disease progression^[7].

Few studies have examined potential interactions between anti-HIV drugs and cannabis. However, there are theoretical interactions between some protease inhibitors and the drug. Further studies are required to determine whether these occur in practice.

An extract of cannabis has been developed into a drug for multiple sclerosis called Sativex. This is taken as a spray under the tongue. An artificial form of cannabis’ active ingredient delta 9-tetrahydrocannabinol (THC) is also licensed, as dronabinol (Marinol). These preparations do not cause the ‘high’ of the illegal drug.