On May 23 of this year, 13 semi-eminent British scientists and doctors signed a statement-with all the stylistic authority of a Papal Edict-condemning homeopathy as "unproven or disproved". No doubt about it, they said, homeopathy is useless, and a waste of money, too. They urged the NHS to stop using it-a negative message widely accepted by the media, at least initially.

Was there anything to the attack? The primary claim of the 13 signatories was that homeopathy is "an implausible treatment for which over a dozen systematic reviews have failed to produce convincing evidence of effectiveness". Sounds totally damning, but is it true? Let's take it point by point.

"Implausible". Certainly, homeopathy is at variance with both conventional scientific theory and the dominant medical model of disease and how to treat it. But implausibility is not a criticism. History is littered with examples of once implausible ideas that are now accepted-aeroplanes, meteorites and continental drift, for example. In medicine itself, helicobacter pylori as a cause of ulcers, folic acid as a preventative of neural-tube defects, and acupuncture used for anaesthesia are just three of the ideas that were considered ludicrous and are now considered fact.

"Over a dozen systematic reviews". That's an underestimate. In fact, an in-depth survey in 2001 located 22 "systematic reviews of clinical trials" of homeopathy in the medical literature (BMC Complementary and Alternative Medicine 2001, 1: 4). That survey was carried out five years ago, and there have been two major clinical reviews since then. So, two dozen would be a more accurate figure.

"Failed to produce convincing evidence". This is the nub of the issue. The word "convincing" is key. Note that the 13 signatories are not saying there's no evidence, it's just that that these particular individuals aren't persuaded by it. Well, that's hardly surprising, given that some of them are (or at least were) members of either Quackwatch or COPUS (Committee for the Public Understanding of Science)-organizations dedicated to rooting out the "irrational" in science and medicine.

However, putting their personal prejudices aside, is there any objective merit to their attack? Let's look at the real evidence.

The 2005 Lancet study
Doubtless, uppermost in the minds of the 13 would have been a very recent survey of homeopathy, conducted by Swiss researchers less than a year ago (Lancet, 2005; 366: 726-32). This attracted a lot of publicity at the time, partly because Dr Richard Horton, the Lancet editor who published the report, penned an accompanying editorial, "The End of Homeopathy", which condemned homeopathy outright: "Now doctors need to be bold and honest with their patients about homeopathy's lack of benefit." Although it wasn't made clear in the media reports, the Lancet study wasn't an actual test of homeopathy. The Swiss researchers did no clinical investigations of their own; it was entirely a paper exercise. What they claimed to have done was an objective assessment of 110 clinical trials of homeopathy-the ones they considered passed a minimum quality standard (roughly 60 per cent of the published trials to date).

The exercise they were engaged in was what's called a meta-analysis. This is a useful tool in standard medical research, because it pools all the clinical data about a particular medicine or treatment, in order to quantify its overall benefit or effect. In theory, the entire process ought to be objective, but in practice it's not. The "rules" of meta-analysis allow the quality of the individual bits of data to be taken into account, thus compromising the objectivity of the process.

The 2005 Swiss study on homeopathy is a case in point. The researchers initially analyzed 110 trials, and found "a beneficial effect", i.e., homeopathy worked. However, they decided to reject 102 of these trials as being of inferior quality. Among those rejected were eight trials on upper respiratory tract infection, whose findings were so positive that the authors decided "the results cannot be trusted". Ultimately, therefore, their final meta-analysis was confined to just eight studies, which unsurprisingly, showed no beneficial effect of homeopathy.

"This was a dubious and biased study," says Dr Peter Fisher, clinical director of the Royal London Homeopathic Hospital. "If they had chosen nine or even seven of the very best trials, they would have got a positive result." That was the headline criticism levelled at the Swiss study, but there were many others-"lack of transparency", "did not follow accepted guidelines", "unacceptable lack of detail", "false conclusions based on false premises" were some of the adverse comments from a wide variety of experts (Lancet, 2005; 366: 2081-6).

The critics' general thrust was that the theoretically dispassionate meta-analysis process had been hijacked by a group of medical researchers with a strong bias against homeopathy from the outset. Indeed, the Swiss authors admitted their prejudice in black and white, commenting that homeopathy seemed "implausible", and that any positive clinical findings could be explained by "bias in the conduct and reporting of trials". Fortunately, in the last few years, there have been a number of less prejudiced tests of homeopathy, and these offer good evidence that it works.

More meta-analyses
The first truly comprehensive review of homeopathy was done about 16 years ago by a team of experts at Limburg University in Holland. It was a two-year study, funded by the Dutch government, which wanted an independent assessment of homeopathy's effectiveness.

The researchers unearthed a total of 105 clinical trials satisfying the basic criteria of being "controlled", i.e., in which homeopathy was compared to a placebo (a dummy pill). Of these, 81 trials showed a positive result in homeopathy's favour.

Although the researchers criticized the "low quality" of most of the trials, there were "many exceptions". This enabled them to conclude that "homeopathy can be efficacious", and so is probably justified "as a regular treatment for certain conditions" (BMJ, 1991; 302: 316-23).

Eight years later, seven medical researchers from the University of Munich carried out a very similar exercise, concluding that 89 trials of homeopathy (out of 185) were suitable for analysis. They computed that homeopathy gave a "pooled-odds ratio" of 2.45, meaning that the clinical benefits were more than twice as good as a placebo.

They concluded with a modestly expressed double negative: "the results are not compatible with the hypothesis that the clinical effects of homeopathy are completely due to placebo". In other words, homeopathy works (Lancet, 1997; 350: 834-43).

Then, in 2000, the European Commission ordered a review from four eminent French clinical pharmacologists, asking them to report on homeopathy to its Science, Research and Development directorate. These investigators employed even more rigorous quality selection criteria than their predecessors, choosing to analyze only 17 out of 118 clinical trials. Again, they concluded that the balance of evidence was in favour of homeopathy, citing a probability figure of 0.000036 (i.e., the likelihood of this being a fluke result is very low indeed), and thus "extremely significant", according to medical statisticians (Eur J Clin Pharmacol, 2000, 56: 27-33).

Apart from the heavily criticized 2005 Lancet review, the most recent "critical overview" was carried out three years ago by a small international team of experts, including one from the Harvard Medical School (Ann Intern Med, 2003; 138: 393-9). They presented a meta-review of all the reviews to date, plus-for the first time-a meta-analysis of homeopathic trials on specific conditions.

Overall, they concluded that while "the quality of clinical research in homeopathy is low. . .when only high quality studies have been selected for analysis. . . a surprising number show positive results". Turning to specific conditions, they again criticized the quality of the basic research as "scant, of uneven quality", but still were able to tease out some pretty clear indications of what conditions homeopathy works best for (see box above).

Power of the Placebo
Apart from the quality of the research, one problem that has bedevilled homeopathic clinical trials is the size of the placebo effect. Homeopaths acknowledge that patients who go through the elaborate consultation process with a homeopathic doctor are likely to have a huge clinical response, even if given dummy placebo pills.

The importance of the doctor-patient relationship in the curative process has been known for millennia, but in the drug-dominated 20th century it has tended to be dismissed and derided as a "mere" placebo effect. Recently, however, the sheer power of the placebo effect has become recognized, as scientists have been able to map the pathways between the brain and the immune system. What the new research shows is that someone's belief in a medicine may boost the body's self-repair system sufficiently to produce a cure-all by itself. This means that any medicine has a mountain to climb in order to show that it is better than placebo-and, of course, the stronger the placebo effect, the higher the mountain.

"I prefer to call it a non-specific effect rather than placebo, but it undoubtedly does form a large part of homeopathy," says Dr Peter Fisher. "It's to do with the art of medicine-the doctor-patient relationship. But homeopathy clearly has specific effects over and above the non-specific ones. Besides, from the patients' point of view, what do they care how the curative effect is achieved? All they're really interested in is getting better".

Assessing just how much patients actually benefit is the latest aspect of homeopathic research. In addition to testing homeopathic medicines as if they were drugs, researchers are now looking at the so-called "outcome". In short, do people really get better with homeopathy (as opposed to a placebo effect), and how does that compare with other types of medicine?

The largest outcome survey has been done by doctors at the Bristol Homeopathic Hospital. They analyzed over 23,000 outpatient consultations from 1997 to 2003, and found that over 70 per cent of their patients reported "clinical improvement". Particularly striking is the fact that many of their patients had chosen homeopathy only after mainstream medical treatment had failed them.

The biggest improvements were found in children, with over 80 per cent reporting a positive health change. The conditions most improved were childhood asthma, eczema, chronic fatigue syndrome, Crohn's disease, IBS, depression, headache/migraine. menopausal symptoms and arthritis (J Altern Comp Med, 2005; 11: 793-8). "Homeopathy's clinical potential may be much wider than current [randomized control trials] evidence alone would indicate," says Bristol Clinical Director Dr David Spence. Homeopathy and animals One of the areas rarely covered in the homeopathy debate is the evidence from vets. There are now close to 100 fully qualified vets in the UK who have largely abandoned conventional drug-based medicine in favour of homeopathy-simply because they find it works better. These alternative vets don't just operate in the cosy world of pets, but also in the hard commercial world of farming, where sick animals cost money and farmers want results.

One of the pioneers of veterinary homeopathy is Oxfordshire vet Christopher Day. He runs a thriving practice for "last-resort" pets, and over the last 20 years has amassed thousands of case histories of animals he has saved using homeopathy, often after conventional medicine has failed. His most impressive cases, however, are with farm animals. He has been able to eradicate difficult-to-treat conditions like New Forest Eye and udder disease in cows, simply by adding a homeopathic remedy to the animals' water.

Day has done some very successful clinical trials. In one study of the effect of homeopathy on the rate of stillbirths in pregnant pigs, he showed that untreated pigs had an 80 per cent incidence of stillbirths, compared to 30 per cent among the treated pigs (Inter J Homeop, 1986; 1: 26-8).

In another classic double-blind study, he compared the rates of mastitis in two groups of 40 cows. Although housed in the same shed, the cows were physically separated and had different water supplies. A homeopathic remedy was added daily to the water of one group, and a placebo remedy to the other's. The results were staggering. While there was a 48 per cent incidence of mastitis in the untreated cows, the figure for the treated cows was just 3 per cent (Inter J Homeop, 1986; 1: 15-19).

To date there have been nine RCTs studying the effect of homeopathy on farm animals-all successful. These alone offer powerful evidence that the conventional explanation of homeopathy-as nothing more than a placebo effect-finally won't wash.

Tony Edwards