First and foremost, I want to mention that possession of cannabis is a criminal offense, 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 CUPID (Cannabinoid Use in Progressive Inflammatory brain Disease) study at the Peninsula Medical School in Plymouth has reached an important milestone with the news that the full cohort of 493 people with multiple sclerosis (MS) has been recruited to the study. CUPID is a clinical trial which will evaluate whether tetrahydrocannabinol (THC), one of many compounds found in the in the cannabis plant (and the main active ingredient) is able to slow the progression of MS. This is an important study for people with MS because current treatments either target the immune system in the early stages of MS, or are aimed at easing specific symptoms such as muscle spasms or bladder problems. At present there is no treatment which slows progression of the disease.

The CUPID trial follows an earlier study -- Cannabinoids and Multiple Sclerosis (CAMS) -- which suggested a link between THC and the slowing of MS. The CAMS trial saw participants take THC for a year -- the CUPID trial will last for longer and aims to assess the effect of THC on progressive MS. It has taken two years to recruit the 493 participants who will each take part in the trial for three years, and in some cases three and a half years. After data cleaning and analysis the results should be available by spring/early summer 2012.

Professor John Zajicek from the Peninsula Medical School, who heads the team carrying out the CUPID study, said: "We are delighted to have achieved the correct number of patient participants for this trial. Patients have been recruited from 27 sites across the UK. If we are able to prove beyond reasonable doubt the link between THC and the slowing down of progressive MS, we will be able to develop an effective therapy for the many thousands of MS sufferers around the world."

The CUPID trial is funded by the Medical Research Council, the Multiple Sclerosis Society and the Multiple Sclerosis Trust. Chris Jones, chief executive of the MS Trust, commented: "The MS Trust is delighted to be supporting this study on behalf of people with MS. The ability to halt progression in MS is what we dream of - the Holy Grail for those whose condition deteriorates year on year. This study should give us the definitive answer as to whether cannabinoids will prove to be such an agent."

Dr Laura Bell, research communications officer for the MS Society, said: "People affected by MS are keen to know whether there's any truth in the suggestion that elements of the cannabis plant can help ease the symptoms and slow down progression of the condition. "The MS Society is supportive of safe clinical trials investigating the medicinal properties of cannabis and it's great news that this trial is going ahead. We look forward to the results of this exciting study."

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-quarter 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.

Sources: ScienceDaily.com and BBC Health -Ask the doctor (Dr Trisha Macnair)