Many complementary medicines contained dangerous levels of arsenic, mercury and lead, and could be potentially deadly, a leading forensic pathologist has warned.
Professor Roger Byard from the University of Adelaide has warned against the "false perception" that herbal medicines were "safer than manufactured medicines" after publishing a study which revealed their toxic contents.
"Many contain potentially lethal concentrations of arsenic, mercury and lead," Prof Byard said.
"These substances may cause serious illnesses, exacerbate pre-existing health problems or result in death, particularly if taken in excess or injected rather than ingested."
Prof Byard's paper, published in The Journal of Forensic Sciences, includes cases of children who developed lead and arsenic poisoning after they were given complementary medicines by well meaning parents.
He said the risk came not only from toxic substances found in some natural therapies but also from their problematic use alongside conventional drugs.
"Herbal medicines are frequently mixed with standard drugs, presumably to make them more effective. This can also have devastating results," Prof Byard said.
According to Prof Byard, St John's Wort was known to reduce the effectiveness of warfarin and could also cause bleeding in women taking the oral contraceptive pill.
Complementary Healthcare Council executive director Dr Wendy Morrow accused Prof Byard of seeking to cause unnecessary alarm.
"I believe this is inflammatory and designed to cause panic," Dr Morrow said.
"Every medicine has an effect on the body and so every medicine should be treated with respect regardless of whether it is a pharmaceutical or a complementary medicine."