The idea that herbal medicines are ‘safe’ because they come from natural materials could be dangerous.

Researchers have uncovered a range of issues relating to the preparation of complementary medicines (including herbal products) and their use, finding some traditional herbal preparations contain toxic chemicals from animals and plants, as well as heavy metals and pesticides.

“Toxic side effects of herbal medicines used in traditional societies have typically not been reported, and this is often cited in favour of their safety,” lead author Professor Roger Byard, Professor of Pathology at the University of Adelaide.

The lack of proper observation has meant that even serious adverse reactions, such as the kidney failure and liver damage caused by some plant species, have gone unrecognised until recently.

The review – by researchers from the University of Adelaide, Murdoch University and Curtin University – has important implications for consumers, as more than half of those using complementary medicines (including herbal products) do not inform their doctors of use.

Patients often use these products alongside conventional medications and with other herbal medications.

“Most of the time patients don’t recognise herbal products as a medicine, so it doesn’t come to mind when asked what medicines they are taking,” says co-author Dr Ian Musgrave from the University's Discipline of Pharmacology.

“It can also be a situation of 'don’t ask, don’t tell' – medical doctors may not think to ask patients what herbal medicines they might be taking, so people don't think to mention it.

“The problem with this is that drug interactions are poorly recognised in herbs – not only can herbal medicines interact with traditional pharmaceutical medicines but also with other herbal medicines the patient may be using.”

The authors say that due to relatively light regulation of the industry, the content and quality of herbal preparations are not as tightly controlled as standard pharmaceuticals.

“A significant number of traditional herbal medicines do not comply with Australian regulations,” Dr Musgrave says.

“In some cases ingredients are either not listed or their concentrations are recorded inaccurately on websites or labels. In other cases a botanical species may be replaced with another if it is difficult to source or too expensive. The replacement species may be potentially toxic. Most worryingly, a few products are illegally adulterated with standard pharmaceuticals to increase the effectiveness of the herbal product.”

The experts are calling on the Therapeutic Goods Administration to require manufacturers to have samples independently tested before placing them on the market, and for legal action to be considered in cases of non-compliance with applicable regulations.

Dr Musgrave says: "Any sensible way to overcome these issues will involve more effort: more testing, more documentation, and this will naturally incur more costs for industry.

“There will be a reluctance from industry to do this, but while they claim that for thousands of years they have been using herbal products without such tests, the potential risks to human health mean that there is due cause for reasonable, scientifically rigorous testing.”

The study is accessible here.