It is reported by the British Medical Journal this week that a study in the UK has indicated that acupuncture could be helpful for migraine sufferers. In Germany, however, where researchers have conducted the largest clinical trials of acupuncture ever undertaken, the results are not so clear cut. About 500,000 patients were included in these ambitious projects which are sponsored by four large health insurance companies. Previously, acupuncture research suffered from the fact that clinical studies were small, often too small to allow meaningful conclusions. A typical trial would include 50 patients and anything bigger than 100 was already seen as remarkable.

Even the background of these mega-studies is fascinating. In October 2000, the German authorities decided that the evidence for acupuncture was not sufficiently convincing for inclusion in the list of interventions qualifying for reimbursement from health insurance companies. Henceforward Germans would have to pay for acupuncture out of their own pockets, as do most people in Britain.

This announcement created uproar - German doctors who had previously used acupuncture, and received money from health insurers for it, feared that their income would decrease. After intense lobbying it was agreed that acupuncture would be put to the test, and that German doctors experienced in acupuncture could participate in these trials. Crucially, they would be paid for doing so. So doctors were happy to take part and patients thought this was a good way of continuing to enjoy "free" acupuncture treatments.

Several "cohort studies" were started as part of the overall project. These are investigations where all patients receive treatment and the results are monitored and compared to their respective baseline values. Lacking a comparison or control group, such results have to be interpreted with the greatest of caution. But the researchers from Munich, Berlin and Bochum were also keen to embark on more rigorous tests. So they initiated four large controlled clinical trials to determine the usefulness of acupuncture for four conditions: chronic back pain; chronic arthritis of the knees; tension headache; and migraine. These trials also involved univer sity departments at Marburg, Heidelberg, Bochum and Mainz.

Patients were allocated at random to one of three treatment groups: real acupuncture plus standard medical care; sham acupuncture (needles were simply stuck into non-acupuncture points) plus standard medical care; or standard medical care alone. The trials are not yet finished - they were due to end about now, but recruitment was slow and recently it was announced that the deadline has been extended until the end of this year. Preliminary results were leaked nevertheless. They are intriguing: adjunctive acupuncture turned out to be better than standard care but sham acupuncture yields the same benefit as "real" acupuncture.

This is perplexing because it could be interpreted in two dramatically different ways. The optimist (or acupuncturist) would say that the results demonstrate the effectiveness of acupuncture - adding it to standard care improves the outcome compared to standard care alone. Hence acupuncture must be a good thing. On the other hand, the pessimist (or scientist) would insist that these results prove that acupuncture is merely a placebo therapy with no "real" effects of its own. It doesn't matter where we stick the acupuncture needle, the patient improves in any case, and this can only be due to a placebo response. Hence acupuncture has no "real" value.

So do the German mega-studies suggest effectiveness or ineffectiveness? Apparently, there is less room for interpretation than one might think. One of the German investigators, Professor H J Trampisch from Bochum University, recently provided the answer. When asked whether these results demonstrate the success of acupuncture his response was decisive: "No, this cannot be. In our studies, we clearly determined that acupuncture will be deemed effective only if it is significantly superior to sham acupuncture".

If this is true, the biggest trials in the history of acupuncture might be the beginning of the end of this therapy.

· Edzard Ernst is professor of complementary medicine at the Peninsula Medical School at the universities of Exeter and Plymouth.