The study's authors have revealed that over the last two decades, a lot of studies have promoted the effectiveness of herbal medicines, but most clinical research has involved standard preparations or single herbal extracts rather than the individually tailored treatments favoured by herbal medicine practitioners.
They also say that such studies have been sponsored by manufacturers, who are eager to cash in on the growing market for over the counter remedies.
During the study, the researchers analysed the available comparative clinical research on individually tailored herbal medicine treatments. They involved published articles and research databases in the analysis, and also contacted health experts and professional bodies.
It was found that only three out of more than 1300 were randomised controlled trials of sufficient quality to draw meaningful conclusions. The three studies covered the treatment of knee osteoarthritis and irritable bowel syndrome, and the relief of side effects caused by drug treatment for cancer.
The authors claim that they did not find any statistical differences between tailored herbal medicine and placebo in either the knee osteoarthritis study or the cancer treatment study.
The say that though tailored herbal medicine treatments seemed to work better than placebos in irritable bowel syndrome, they were not as good as standard preparations.
"...There is no convincing evidence that (individualised herbal medicine) is effective in any indication," conclude the authors.
They have also warned that individualised herbal medicine may cause side effects, and that they have the potential to react badly with other herbs and prescription medicines.
In an accompanying editorial, Professor Edzard Ernst, of the Peninsula Medical School at the University of Exeter, cautions that people often confuse phytotherapy, which represents the scientific face of herbalism, with traditional herbal medicine and over the counter remedies, which currently have no basis in science.
He says that phytotherapy has considerable potential to benefit patients, whereas over the counter remedies and traditional herbal medicine can harm those who use them.
"Without these distinctions, we will fail to advance our knowledge of the potential benefits of herbal treatments. More importantly, we will also fail in our foremost duty - to protect the public from treatments that cause them harm," he concludes.