January 28, 2004
Helen R. Pilcher , Nature
This Thursday sees the downgrading of cannabis from a class B to a class C drug in Britain, putting it on a par with tranquillizers and steroids.
Many people welcome the move, but it has also sparked controversy. Some caution that cannabis can trigger mental illness, whereas others maintain that the drug is medically useful.
In Britain, drugs are grouped into three categories. Class A drugs include heroin and morphine, class B drugs include amphetamines and barbiturates, and those in class C, now including cannabis, are judged to be the least damaging.
Under the reclassification, the possession, production and supply of marijuana are still illegal, but the penalties are different. Adults found carrying the drug are now more likely to receive a warning than a prison sentence. And the maximum prison sentence for possession has dropped from five to two years. Legally, this brings Britain in line with some European countries such as the Netherlands, although in practice these laws are likely to be more strictly enforced in Britain.
An estimated three million people in Britain take cannabis each year, some for medicinal reasons, but most for recreational use. This includes one-quarter of those aged between 16 and 24.
The long-term effects of smoking marijuana are uncertain. Some argue that cannabis can trigger schizophrenia, but the evidence for this is controversial. A recent government report1 concluded that there is no clear causal link between cannabis and mental-health problems. But Robin Murray of the Institute of Psychiatry in London disagrees. 'Cannabis nearly always exacerbates symptoms in people that already have mental-health problems,' he says.
Murray has assessed cumulative data from five recent studies looking at cannabis use and schizophrenia. People who use cannabis are twice as likely to develop schizophrenia than non-users, he concludes.
That said, the overall risk is low. Most people who smoke dope don't develop psychosis. But some may be more vulnerable to the drug's mind-altering effects than others.
Marijuana use may have other adverse health effects too. Regular smokers - of cannabis or tobacco alike - are more likely to develop lung cancer and respiratory problems such as asthma. And controversial studies have shown that the drug can lower sperm counts in men and suppress ovulation in women1.
But the drug may have positive effects for some. Marijuana is thought to dull chronic pain and may ease the symptoms of multiple sclerosis (MS), an incurable disease of the nervous system that causes spasms, pain and tremor.
In a recent large-scale trial, 60% of MS patients who took synthetic cannabis said it helped their mobility and eased their pain and muscle stiffness. 'It doesn't suit everyone, but it does suit some,' says Clare Hodges, MS sufferer and founder of the Alliance for Cannabis Therapeutics, a pressure group that lobbies for the medicinal use of marijuana.
About 10,000 seriously ill patients in Britain use cannabis to control their symptoms, says Hodges. Sufferers tend to smoke or eat the drug.
The reclassification isn't expected to make much difference to those who already take the drug, as it has been readily available for some years. But it may make life easier for those who use it medicinally, as arrests for cannabis possession are expected to become less frequent.
'We hope that the prosecuting authorities will treat self-medicating patients sympathetically,' says David Harrison, a spokesperson for Britain's Multiple Sclerosis Society.