Attempts to invent a safe and effective diet pill have foundered time and again, allowing the internet trade in illegal and ineffective herbal supplements and dangerous drugs, such as DNP, to flourish.
A successful diet pill could make billions for the pharmaceutical industry, but efforts to date have ended in disaster, with patients harmed, drugs banned and massive compensation paid out.
Fen-phen, an appetite suppressant, was the most spectacular failure. It was withdrawn in the US in 1997 after causing widespread heart valve damage.
More recently, two other appetite suppressants have been taken off the market in the UK – sibutramine (Reductil) and rimonabant (Acomplia). Both went through the extensive trials required to get a licence and appeared to work, but once they were being widely used, dangerous side-effects emerged.
Rimonabant made some people feel suicidal. Sibutramine increased the chances of having a non-fatal heart attack or stroke.
The only drug that has official NHS approval – orlistat, sold under the brand name Xenical – is unpopular. It works by preventing the absorption of fat in the gut and often causes diarrhoea. It does nothing to dampen the appetite. The National Institute for Health and Care Excellence recommends it for obese patients, but only if they have managed to lose 2.5kg (5.5lb) over four weeks through dieting. It must be stopped after 12 weeks if they have not lost more than 5% of their bodyweight.
Two other drugs used in the UK are not available from NHS GPs. The appetite suppressants phentermine and diethylpropion date back to the 1960s and are privately prescribed by doctors working in slimming clinics. They are legal, after a failed attempt to ban them 10 years ago, but are not in the prescribing guides used by NHS GPs.
The tale of the appetite suppressants that are used, but not NHS-approved, is just one of the bizarre aspects of the world of diet drugs. They were in use until the Fen-phen scandal caused a climate of hostile opinion, according to Robert Houtman, the managing director of the National Slimming and Cosmetic Clinics chain.
"There was a big press campaign against appetite suppressants in the US," he said. The UK government "decided to get on the bandwagon and have these dangerous, addictive drugs banned".
But a report by the Medicines Control Agency in October 1995 found no reason to do so, partly because of a dearth of research on the drugs. It concluded there was insufficient evidence of significant harm to the public from the use of the drugs in slimming clinics.
When the European Medicines Agency nevertheless announced it was revoking the drugs' licences, the pharmacist Tom Chapman, who manufactures phentermine and diethylpropion at his family business, Essential Nutrition, in Brough, near Hull, fought the decision in the European courts and won in January 2003.
Chapman supplies the private slimming clinics of the Obesity Management Association, of which he and Houtman are founder members.
"We only supply OMA members," he said. "That's been a long struggle as well. Originally, doctors were selling it from car boots and all sorts and it was getting a really bad reputation. So we stopped that and said you've got to have premises – proper premises."
How well the drugs work is a matter of debate. The OMA claims a survey of 947 patients at 20 clinics showed they lost an average of 9.6kg, 9% of their bodyweight, over 12 weeks. But people taking the drugs also get weekly consultations with a doctor and diet plans and exercise as well, which might account for the weight loss.
Herbal remedies and supplements have been disappointing. Hoodia, derived from a cactus plant, once looked highly promising. It is chewed by the San hunter-gatherers of southern Africa during long expeditions to stave off hunger. Although South African government scientists isolated the active ingredient and patented it, neither Pfizer nor Unilever could create a viable product.
Pfizer collaborated with the UK's Phytopharm, which had bought the rights to develop it from the South African government. But Pfizer said it proved too expensive to synthesise the active ingredient and pulled out in 2002, though its lead researcher wrote to the New York Times in 2005 to say it had found "indications of unwanted effects on the liver caused by other components, which could not be easily removed from the supplement".
Unilever, which owns Slimfast, took up the baton, but in turn dropped the partnership with Phytopharm in 2008. A study published in the American Journal of Clinical Nutrition showed it did not work – and there were side effects, including nausea and raised blood pressure and heart rate.
Hundreds of hoodia products, claiming to be based on extracts of the plant (protected under Cites conservation rules) are sold as herbal remedies. But most of the products on sale contain no genuine hoodia at all; one study showed 80% were fake.
