First and foremost, I must point out that possession of cannabis is a criminal offence, although the police are more lenient with those possessing small amounts for their own personal medical use.
There have been claims cannabis may have beneficial effects in a variety of medical conditions, including MS, severe nausea and vomiting (for example, during chemotherapy), glaucoma, chronic pain and migraine.
The problem is many of these claims are little more than anecdotal evidence - personal reports from people who've tried it, or treated someone with it. Reliable scientific evidence based on properly conduced clinical trials has been sparse.
The Cannabis in Multiple Sclerosis (CAMS) trial, funded by the Medical Research Council and published in The Lancet in 2003, demonstrated some of the uncertainty about the benefits of cannabis in alleviating MS symptoms.
More than 600 people took part in the trial, which was examining the effects on spasticity. They took oral capsules containing either whole cannabis extract, or tetrahydrocannabinol (THC), the drug's principal active ingredient, or a placebo (dummy treatment).
The trial was blinded so that participants didn't know what they were taking.
The researchers weren't able to show a significant improvement in spasticity among those treated with cannabis extract, or THC, even though the participants reported an improvement in their symptoms, in particular pain, spasms, spasticity and sleep quality, but not irritability, depression, tiredness, tremor or energy levels.
The researchers did find that patients taking the cannabis derivative showed an improvement in their ability to walk.
The researchers also pointed out that three-quarters of the patients given cannabis had guessed they were taking active medication, and half of those receiving placebo had guessed they weren't receiving cannabis.
The researchers concluded the study had yielded no definitive verdict on whether or not cannabis eases the symptoms of MS. They added that many of those taking placebo capsules containing no active treatment felt benefits, which indicated how much patients gain by taking part in clinical trials, irrespective of the treatment they are given.
Increase in medicinal cannabinoid trials
In the past two to three years, there's been a dramatic increase in the number of clinical trials investigating medicinal cannabinoids - synthetic drugs based on the active chemicals isolated from cannabis - in MS.
These medicines, such as a delta-9-THC buccal spray, have been tested for the treatment of symptoms such as chronic pain and spasticity, and most of the studies suggest they have a helpful effect, at least for a subgroup of patients.
Risks are as unclear as benefits
Just as the benefits have yet to be proven, so the risks remain unclear. Cannabis undoubtedly has psychoactive effects (this is, after all, why people use it as a recreational drug).
There's research to show that cannabis may cause short-term memory problems, poor concentration and slowed reaction times during acute intoxication.
There is also some evidence to suggest long-term use of cannabis may increase the risk of psychosis, especially in certain people who are more vulnerable.
The risk of long-term psychological harm and the issue of whether cannabis use leads to the use of other drugs are the subject of heated debates.
Herbal cannabis contains hundreds of chemicals, which could be having different effects, and it's difficult to know what you're getting and in what dose when you smoke it.
Researchers looking at purified medicinal cannabinoids say adverse side-effects have generally been mild compared with the other drugs used to treat pain and spasticity in MS. Even so, there's concern about potential long-term effects, in particular psychiatric effects, and adverse effects on foetal development.
Prescribed cannabinoids may be the best choice
The only legal option if you want to try cannabis as a treatment for MS is to talk to your doctor about medicinal cannabinoids. These contain a synthetic version of THC and are in tablet form. They're legal, easy to take and have a guaranteed dosage.
People who've tried them say they're not as effective as smoking cannabis, but do help to some degree, although side-effects may still be a problem.
This article was last medically reviewed by Dr Trisha Macnair in November 2007
