Herbal remedies can kill - expert

Herbal remedies can kill, says an Australian forensic pathologist, who warns against the "false perception" they are "safer than manufactured medicines".

Professor Roger Byard, from the University of Adelaide, said the risk came not only from toxic substances found in some natural therapies but also from their problematic use alongside conventional drugs.

St Johns Wort was known to reduce the effectiveness of warfarin, the drug which prevents blood clots from forming in people who have had a heart attack, Prof Byard said.

The popular herb could also cause bleeding in women taking the oral contraceptive pill, he said.

"Herbal medicines are frequently mixed with standard drugs, presumably to make them more effective," Prof Byard said.

"This can also have devastating results."

Other seemingly innocuous therapies - Borage Oil and Evening Primrose Oil - were known to lower the seizure threshold for epileptics while Gingko and garlic increased the risk of internal bleeding.

Prof Byard said many people who took complementary medicines did not tell their doctor, despite the risks.

He also analysed 251 Asian herbal products found in stores across the US and he found arsenic in 36 of them, mercury in 35 and lead in 24 of the products.

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.

"There's a false perception that herbal remedies are safer than manufactured medicines, when in fact 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 is calling on forensic pathologists to be more alert to the role that herbal therapies could play in unexpected deaths.

Australians spend $2.5 ($NZ3.14) billion on complementary therapies a year, according to the latest industry estimate.

The Complementary Health Care Council of Australia said therapies containing toxic substances were unlikely to be made or sold within Australia though they were available over the internet.

Executive director Dr Wendy Morrow also accused Prof Byard of seeking to cause unnecessary alarm.

"I believe this is inflammatory and designed to cause panic," Dr Morrow told AAP.

She said information was available from complementary medicine makers where there were potential drug-herb interactions.

Consumers should always look for an "AUST L" or "AUST R" number printed on the front of complementary medicine packaging, Dr Morrow said, as this showed it complied with standards set by the Therapeutic Goods Administration.

"There is not a wide-held belief that complementary medicines are 100 per cent safe," she also 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."

- AAP