Evening Standard (London): Why I've changed my mind about cannabis

'I can't think of a single patient of mine with a serious mental illness who hasn't used the drug in the past'

CANNABIS use among schoolchildren has risen tenfold over the past 20 years, despite growing concern that teenagers' brains appear to be particularly susceptible to the drug, putting them at significant risk of severe mental illnesses like schizophrenia.

According to the latest study by the Schools Health Education Unit, one in 16 12-year-olds, and one in four 15-year-olds, now admits to having used the drug, up from one in 50 and one in 100 respectively in a similar survey in 1987 - the same year that researchers first identified a possible link between cannabis use and mental illness.

Since then numerous studies have shown that schizophrenia is far more common among regular cannabis users - around seven times more common in people who have used the drug on at least 50 occasions. The lifetime risk of developing schizophrenia for the average person is around one in 100, meaning that regular cannabis users are playing Russian roulette with a one-in-15 chance of developing an illness that often lasts a lifetime.

And the latest research suggests that the younger the brain, the higher the risk. A study in New Zealand found that children who had started using cannabis by the age of 15 were nearly five times more likely to develop serious mental illness by their late twenties than those who started at 18.

Neuroscientists suspect that the increased susceptibility of young teenagers is because the brain continues to develop and mature during the teen years - something that has only been discovered recently.

Drug abuse is thought to influence this final phase of brain formation, increasing the risk of the type of functional and chemical imbalance associated with mental illness.

I used to take a fairly liberal stance on cannabis and in the past have compared it favourably to alcohol and tobacco, both of which exact a considerably bigger toll on our society than all the illegal drugs combined.

But as a parent of two teenage girls I have become increasingly concerned about the link with mental illness.

It is a concern reinforced by my own experiences in practice. While only a small proportion of cannabis users will be unlucky enough to develop schizophrenia, I can't think of a single patient of mine with a serious mental illness who hasn't used the drug in the past. Hardly evidencebased medicine, I know, but cannabis has become a depressingly common feature in the past history of young people with serious mental illnesses. It is vital that the public are aware of the potential dangers.

Cannabis is still perceived by many as a "safe" drug, but there is now a growing pile of evidence that it is anything but. Most people who try it will come through unscathed, but for some, particularly those who use it regularly, it will leave a permanent scar on their brains that could cost them their friends, family, career, and possibly even their lives.

For more advice and information on schizophrenia and other serious mental illnesses visit www.sane.org.uk

Getting weight loss all stitched up FIVE hundred obese people had their stomachs operated on last year under the NHS to reduce their appetite and help them lose weight - twice the number who underwent the procedure in 2003, a trend that can only accelerate.

The National Institute for Clinical Excellence (NICE) approved the use of surgery for obesity back in 2002, but only in patients who meet its strict criteria. To be eligible you have to be severely overweight (Body Mass Index of more than 40, or more than 35 if you have a weightrelated health problem such as diabetes). And you must be aged over 18 and have tried and failed to lose weight using diet, exercise and slimming tablets under expert guidance.

But even under these tight criteria, more than a million people in England and Wales are still likely to be eligible, and if experience from the Continent is anything to go by then the NHS is going to have to dig much deeper to meet future demand - 17,000 obese people underwent this type of surgery in France alone last year.

Severely obese people can expect to lose an average of six to eight stone over two years following stomach-reducing surgery, at least four times as much as they're likely to lose on a more conventional dietand-exercise plan.

. For more information on the procedures available, side effects and success rates, visit the Technology Appraisals section of www.nice.org.uk

Waiting times are back in the headlines after King's College Hospital caused a furore by writing to accident victim Rachel King to tell her that she could be waiting more than 18 months for an MRI scan unless she paid to jump the queue and get it done privately. King's quoted Rachel Pounds 983 for the private scan, and told her that she would only have to wait two weeks. That's five times the cheapest quote I found - Pounds 198 at Linton House in Cheltenham (01242 535910), which could do it the next day.

The fact that one of our top hospitals provides such a poor service is worrying enough, but to capitalise on its failure by overcharging desperate patients who opt for the private option is inexcusable. Don't fall victim to private MRI services that are capitalising on the NHS's current underprovision - phone around and be prepared to travel.

AND while I am on the subject of weight loss, this week's prize for silly research goes to a team from Tennessee which managed to keep a straight face while presenting its study into how laughter can help you slim, to colleagues at a congress on obesity in Athens.

The researchers used volunteers to help them calculate the amount of additional energy burnt by laughing, reckoning it to be as much as 160 calories an hour. So laughing for 10 to 15 minutes a day, they conclude, could increase the average person's calorific requirements by enough to burn off four pounds over 12 months.