Could this be the moment when alternative medicine finally gets the reputation it deserves and is seen for what it is - a massive social and intellectual fraud? Everything that is wrong with complementary and alternative medicine is contained in the two stories that have dominated the news this week - the discovery that Radovan Karadzic had reinvented himself as a white-haired guru offering homeopathy, energy medicine and acupuncture, and the story of Dawn Page, a woman who is now brain-damaged after she went on a "detox diet". For alternative medicine is not only founded on lies and falsehoods, but it can be very bad indeed for your health.

This largely unregulated and unaccountable industry is worth an estimated pounds 4.5bn in the UK. It is used by one in three of us. There are more alternative practitioners than there are GPs in this country, reiki "healers" are employed by the NHS and every chemist has shelves stacked high with alternative remedies. Alternative medicine users - who are mostly middle-aged, middle-class women - are apparently prepared to suspend all normal critical faculties when they encounter an alternative practitioner, even one like Karadzic, who claimed to be able channel energy into his own head via his repulsive topknot.

You don't need to be able to speak Serbian to recognise Karadzic's website as a classic of the altmed internet genre. As well as listing the usual contradictory ragbag of therapies familiar from the windows of the high-street altmed clinic - homeopathy, acupuncture, aromatherapy, Ayurvedic medicine and the like - it is peppered with the universal language of what Americans call "Woo": wellbeing, harmony, bioenergy and, most revealingly, "quantum". There's the long list of ailments he claimed to be able to treat, everything from diabetes to sports injuries and asthma. There are the pendants that supposedly protect the wearer from negative energies and, disturbingly, phallic objects apparently employed to both diagnose and cure.

Under the name of Dragan David Dabic he gave lectures on meditation and yoga and was keen to promote himself in alternative health magazines and at conferences. As an alternative practitioner, he fitted right in.

There's no indication of his credentials, but then credentials in alternative medicine are pretty much worthless. Barbara Nash, the alternative practitioner who developed the "Amazing Hydration Diet" that allegedly ruined the life of Dawn Page, has a diploma from the College of Natural Nutrition, based in Tiverton, Devon. This college sees "human beings as part of nature's system within the enormity of the world and the universe" and its unaccredited correspondence courses cost more than pounds 1,000 a year.

But it's worthless because it is not necessary to stump up the fees, since in this country anyone can set themselves up as a "nutritional therapist" without any qualifications. If you want reliable dietary advice it is dietitians, not nutritional therapists, who are properly trained to provide it.

Page wanted to lose weight and claims that she was advised by Nash to drink four pints of water a day and to cut out salt from her diet. Nash denies any fault, and although she paid Page a settlement of pounds 810,000 last week, she did so without admission of liability. But whatever Nash did or did not advise, nowadays such advice to drink large amounts of water is found in every woman's magazine - and yet it has no scientific basis and is known to be dangerous, even fatal, if done to excess. Page began to feel ill and vomit soon after starting the regime, but claims that she was reassured by Nash that this was a good sign and showed that the diet was working. She now suffers from epilepsy and has severe speech, memory and concentration problems.

Many "nutritional therapists" offer so-called detox diets, despite the fact that they never seem to identify the so-called toxins they claim to be banishing from the body, or any proof that these substances have actually gone. They often use the detox as a marketing opportunity for additional treatments and dietary supplements and if any user complains of feeling unwell, they say that this is a "healing crisis" that shows the detox is effective. They often claim, with no supporting evidence, that their regimens "boost the immune system" or "rebalance energies".

So if these cases are not unusual, how can you protect yourself from dangerous quackery? Even a cursory exploration of the world of alternative medicine reveals that many quacks back up their ludicrous claims with the same old ideas, however different their supposed treatments. These common identifiers will help you spot a quack.

For a start, quacks often use language that is abstract and subjective but is ultimately meaningless. Words such as "quantum" sound impressive to those of us with only a weak grasp of theoretical physics, but are in fact nothing but pseudo-scientific window dressing designed to lure a gullible public.
Their therapies are frequently based on "ancient wisdom" and their methods never change, regardless of any new evidence about their efficacy (or the lack of it). Sometimes this is not even true, as in traditional Chinese medicine, which claims to have been transposed intact over several millennia but in reality was fashioned from a ragbag of disparate therapies in post-revolutionary China because Mao could not afford to provide scientific medicine for the Chinese people. Similarly, the foot massage therapy called reflexology was invented in the US in the 1930s, and ear acupuncture by a French doctor in the 1950s.

Quacks will often tell you that feeling worse is a sign of getting better. Most detox regimes describe symptoms such as spots, bad breath, headaches and nausea as proof that the detox is working. Such a notion is central in homeopathy, which enables practitioners to rationalise away the worsening of their patients' symptoms.

Quacks often claim a success rate of around 80%, a figure not too high to be totally unbelievable but that is irresistible to prospective customers. In the name of "treating the whole person" they tend to diagnose the same disorder in every patient. One popular US therapist, Hulda Clark, in her books The Cure for All Diseases and The Cure for All Cancers, says that all illness is caused by either pollutants or parasites. Or you could put it another way: the orthodox doctor treats what you have, and the alternative practitioner says you have what she treats.

Quacks often say a powerful establishment is trying to suppress the discovery that they have made. They'll claim that doctors and pharmaceutical companies don't want you to know about natural cures because it would do them out of a job. At worst they accuse the medical profession of actively trying to make you ill and even of trying to suppress a cure for cancer. They like to say that drug companies aren't interested in remedies found in nature because these substances can't be patented, even though as much as a third of all modern medicines are derived from plants and many of the pharma ceutical multinationals are working closely with Chinese herbal medicine manufacturers, such as the company Chi-Med, to create new medicines for a world market.

Crucially, the evidence for quacks' claims is anecdotal and supported only by testimonials. Best of all is the practitioner who claims to have cured himself, who is often to be found in the area of problematic conditions such as chronic fatigue syndrome, for which orthodox medicine offers relatively little and in which desperate sufferers are easily encouraged to spend thousands of pounds on a myriad of useless alternative treatments, everything from vitamin injections to colour therapy.

Quacks are flattering and will appeal to your vanity. They tell you that you are unique and extraordinary and not like other people. On the rare occasions that they find nothing wrong they say you need maintenance treatment "in order to keep your energies in balance". One chiropractic guru, when asked what to say to the patient who asks how long they should have treatment, said the pat answer should be "only as long as you want to stay healthy".

Still, many aficionados, when they've finished saying "It works for me" like to move on to assert "What's the harm?" and suggest that even if the benefits of alternative medicine can't be proved, it is always wholly benign. The improvements may be due to the placebo effect, they say, but so what? It's true that many of these therapies won't do you any damage, particularly homeopathy, which usually consists to all intents and purposes of sugar pills or water with its active ingredients only in the name. Popular remedies such as "Coldenza," (sugar pills) or "Rescue Remedy" (small bottles of watered-down brandy sold at the equivalent of pounds 399 per litre) may be harmless, but problems arise with remedies such as "Malaria Officianalis" that has been sold as a protection against malaria to people travelling to at-risk countries. It may be harmless in itself, but encourages people not to take proven prophylactics. And many people are encouraged by alternative practitioners to defer or even avoid having orthodox treatment when they are ill, even those with conditions as serious as multiple sclerosis or cancer.

An estimated 25% of Chinese and Indian herbal medicines are adulterated with either heavy metals or by the deliberate addition of pharmaceuticals such as steroids, Viagra and banned amphetamines. Consumers have little or no protection in the UK from the worst kind of practitioners, with the Medicines and Healthcare Regulatory Authority helpfully advising us that it is not currently possible to distinguish between poisonous and adulterated herbal products and those made to acceptable quality and standards.

The ingestion of poisons and dangerous drugs may be one of the greatest risks of alternative medicine, but is not the only danger. People have suffered strokes and even died after having chiropractic neck manipulation, a risk downplayed by the General Chiropractic Council which is confident that the incidence of this kind of stroke "is no more than would occur naturally within the general population". Some risks may be negligible, but are still not worth taking when there is no apparent benefit, such as chiropractic x-rays.

"Chelation therapies" employed to detoxify the body of supposed mercury poisoning have caused serious illness and death. Spurious cancer cures have caused terrible suffering and a cruel dashing of false hope in those at the end of their lives. A BBC TV documentary told the story of a woman with cancer who was instructed by an alternative practitioner to have all her teeth removed by a "holistic dentist" as part of a "toxin/pathogen removal process" at a cost of pounds 2,500. She died five weeks later.

Now websites such as whatstheharm.net and skepdic.com/refuge/harmarchive have begun to catalogue cases of injury at the hands of alternative practitioners, including that of Rosemary Jacobs, whose skin was allegedly turned permanantly grey by the daily drinking of a silver supplement and of those whose ear drums were severely burned by hot wax dripping from an ear candle. Frances Denoon, who claims that she suffered a severe stroke and nearly died after a chiropractic neck manipulation, is campagning in the UK to publicise this risk.

Just because Karadic was a war criminal, it doesn't follow that all alternative practitioners are genocidal maniacs, and indeed many practitioners sincerely believe in what they are doing and want to help their clients. But there have surely been enough cases now of blatant recklessness if not outright deceit to confirm that practising alternative medicine is very often the last refuge of the scoundrel.

· Suckers: How Alternative Medicine Makes Fools of Us All by Rose Shapiro is published by Harvill Secker.