The survey of more than 3000 South Australians during 2004 found 52.2 per cent used complementary and alternative medicine (CAM), such as herbal remedies, aromatherapy and Chinese medicine.
This is higher than other regions of the world such as the US where a 2004 study estimated a third of the population to be using CAM. CAM includes include herbal medicines, Ayurvedic and Chinese medicine, vitamin, mineral and nutritional supplements, homeopathic medicines and aromatherapy products.
The new study also included a range of therapies like chiropractic, osteopathy, naturopathy, homeopathy and acupuncture.
In the Australian research, nearly 40 per cent of CAM users were taking vitamins, more than 20 per cent took herbal medicines and 13.6 per cent were taking mineral supplements.
But while the CAM use was high, the report reveals a decline in spending on CAM to A$1.8 billion in 2004 from A$2.3 billion in 2000. The authors suggest that as there was little change in the numbers using CAMs during this time, and as, in general, there was little change in the cost of the commonly used products, "it is likely that CAM users are now using fewer CAMs per person than in 2000".
This could be in response to the 2003 Pan Pharmaceutical crisis in which a substantial quantity of CAM products was removed from retail stores after government officials found fault with the company's quality control process.
Yet the authors also report that 48 per cent of those questioned wrongly assumed that all CAM products were independently tested by a government authority like the Therapeutic Goods Administration.
Writing in the 2 January issue of the Medical Journal of Australia (vol 184, issue 1, pp 27-31), Alastair MacLennan and colleagues at the University of Adelaide expressed concern that large numbers of people surveyed wrongly believed what they were taking had been tested for quality control.
Another finding that will worry doctors is that half of those questioned took alternative and conventional medicines on the same day and half of these failed to tell their doctor they were using alternative therapies so could not be warned about potential side effects or drug interactions.
"This is in contrast to increasing reports of adverse effects from (these) medicines and other problems seen predominantly overseas, such as contamination, adulteration, substitution, variable dosage, dubious quality control and inappropriate labelling," said the researchers.
They called on doctors to use "open and honest questioning" of their pateints to "factor the effect of complementary and alternative medicines into their assessments".
Researchers also found that a third of parents gave their children complementary medicines. Two thirds of households with children gave their children non-prescribed vitamins.
Most people questioned were not sure what alternative medicines did, but took them to "increase general health".