Cannabis is undoubtedly safer than cocaine or heroin but campaigners for decriminalisation rarely talk about its risks to health.
The adverse effects for regular users, and the medicinal benefits for patients with chronic diseases, are still not fully proven, partly because the drug has more than 4,090 active ingredients. But there is mounting evidence that cannabis can provoke severe anxiety and mental illness, impair reaction times and co-ordination skills and do more damage to the lungs than cigarettes.
Cannabis users take the drug because of its mildly sedative effect, which leads to lower blood pressure, feelings of relaxation and increased sociability. But if cannabis is smoked, users have all the long-term risks of tobacco, such as mouth and lung cancers, bronchitis and increased risk of heart attacks. Modern plant-breeding techniques mean that cannabis has become far more powerful than in the 1960s and some experts now claim that smoking a joint is five times more damaging to the lungs than cigarettes.
In some first-time users, the drug can provoke anxiety, panic and suspicion, and in extreme cases, the drug can precipitate or aggravate schizophrenic attacks. Long-term side effects include distorted perception, slower reaction times, impaired co-ordination and driving skills and lack of motivation. Other studies suggest that young men who regularly take cannabis are more violent.
More adults use cannabis in Britain than any other country in Europe and almost half of all school-leavers are thought to have smoked the drug.
Sufferers of multiple sclerosis and other degenerative illnesses have, for many years, hailed cannabis as the best way of overcoming chronic pain and acute muscle spasms.
In 1997, the British Medical Association concluded that the drug helped people with MS. There was also limited evidence that it was beneficial in epilepsy, glaucoma, asthma, high blood pressure and in the weight loss associated with Aids.
The Government has said it is awaiting the results of two further clinical trials before deciding whether cannabis extracts should be prescribed.
Dr Claire Gerada, head of the Royal College of General Practitioners' drugs misuse training programme, said: "I think it is a good thing not to imprison and criminalise young people. But I would like the public to understand that cannabis is not without risk.
"We have so many deaths from tobacco and alcohol abuse, please let's not go down the same route with cannabis."Reuse content