New research has shown that many people may be putting their health at risk by taking herbal remedies when they are already on conventional medication for other conditions.
A team at the University of Stellenbosch in South Africa carried out an extensive review of existing literature on the topic, included 49 case reports and two previous observational studies detailing 15 separate incidents in which people had become ill.
Each case was analysed to see if medical problems had been created by taking herbal remedies alongside common drugs, based on the pharmacological properties of the active ingredients and the outcome.
The team uncovered dozens of cases where alternative remedies had changed the effects of prescription medicines, whether that was through diluting them, making them work more strongly or creating side effects.
Among the studies was one that saw a man suffer a seizure when his anti-seizure medication was rendered less effective, while problems were also documented among those with heart problems who took remedies including St John's wort and even green tea.
Indeed, herbal medicines had probably played a part in around 60 per cent of the incidents they monitored, the report in the British Journal of Clinical Pharmacology concluded.
First author of the report Charles Awortwe told the Guardian: "If you are taking herbal remedies you should disclose it to your clinician. A potential interaction and its consequences can be very detrimental to the health of the patient."
The University of Exeter's Edzard Ernst added that many people assume natural ingredients cannot be harmful, when they can actually result in potent biological effects.
"It is therefore important that consumers are warned of the danger and think twice before self-medicating with herbal remedies," he said.
It may be that in future, pharmacists are required to carry out routine checks on people wanting to purchase herbal remedies to ensure they are not taking medicine that could be impacted by them.
Last year, NHS England eliminated a number of treatments from being covered by prescription, including homeopathy and herbal supplements widely available in pharmacies and health food stores.
Furthermore, some treatments on the list were referred to the Department of Health for "consideration for blacklisting", Chemist + Druggist magazine reported.