Heart and lungs

Herbal medicines affect heart drugs

“Herbal remedies taken by millions of Britons can pose a serious risk to their health by interfering with medicines commonly prescribed for heart disease,” reported The Times . The newspaper story is based on a review of the available evidence on the potential harms and interactions of herbal products for people who have heart disease.

As the newspaper points out, it is already known that some complementary medicines can lessen the effectiveness of drugs. However, by restating the case and carrying out this review, these researchers are trying to alert those most at risk from these interactions. As this was not a systematic review, it is not possible to say how harmful these remedies are or estimate how often these adverse effects occur.

Anybody considering taking complementary or alternative medicine alongside their own prescribed medication is advised to discuss this with a doctor, nurse or pharmacist first.

Where did the story come from?

This research was carried out In the US by Dr Ara Tachjian and colleagues from the Division of Cardiovascular Diseases at the Mayo Clinics in Rochester, Minnesota and Scottsdale, Arizona. The researchers were funded in part with grants from the National Institute on Aging, the National Heart, Lung and Blood Institute, a Mayo Clinic Marriott Mitochondrial Medicine Award, and the Angel and Paul Harvey Cardiovascular Research Endowment. The study was published in the peer-reviewed Journal of the American College of Cardiology .

The Times and The Daily Telegraph covered this story, with both newspapers providing balanced reports of the science and its implications.

What kind of research was this?

In this literature review, the researchers systematically searched for all published research into the potential harms and interactions of herbal products for people with heart disease.

The review paper gives a detailed description of their research and catalogues the adverse effects of more than 16 herbal remedies found through the literature search. As this is a narrative non-systematic review, and did not quantify the potential harms or how many people are affected, it is not possible to say how harmful these remedies are or estimate how often these adverse effects occur.

What did the research involve?

The researchers used scientific databases (PubMed and Medline) to search for research published between 1966 and 2008 containing the terms: cardiovascular agents, complementary therapies, herb-drug interaction and cardiovascular disease interactions. They do not describe how many articles were found or the criteria used to select them.

They catalogue an extensive list of herbs that either have direct effects on the vascular system or that should be avoided because they interfere with commonly prescribed medication. They then describe the uses for common herbal remedies in the list, for example:

  • St John’s wort, commonly taken for depression, anxiety and sleep disorders.
  • Ginseng taken to prevent ageing, improve immunity, mental and physical capacity and stress tolerance.
  • Ginkgo biloba, which is said to improve circulation and cognitive disorder.
  • Garlic, taken for high cholesterol, high blood pressure and heart disease in high concentrations in pills.
  • Echinacea popularly believed to stimulate the immune system and prevent infections.

The list of herbal medicines examined also includes grapefruit juice, hawthorn, saw palmetto, danshen, tetrandrine, aconite, yohimbine, gynura, licorice, and black cohosh.

The researchers also look at the effectiveness of these medicines in treating the conditions mentioned. They say, for example, that recent randomised trials of ginkgo biloba showed no difference in cognitive impairment measures when the herb was compared to placebo. They highlight St John’s wort because of the potential for serious adverse reactions due to its effect on drug metabolism.

What were the basic results?

St John’s wort
The researchers say that this herb is a particular concern because it can cause an increased metabolism of “more than 50% of all prescription medications”. They list 11 classes of drug that are affected by this faster metabolism and could therefore be made less effective by St John’s wort.

Ginkgo biloba
Several cases of bleeding have been reported when this herb was taken at the same time as antiplatelet, anticoagulant, or antithrombotic agents such as warfarin or aspirin.

Although garlic is thought to lower both cholesterol and blood pressure, this has not confirmed. The researchers say the active ingredient, ajoene, can directly affect platelets (cells in the blood that help with clotting). They say that garlic supplements should not be taken with anti-clotting medication and should be discontinued about 10 days before surgery, especially by patients taking aspirin or warfarin.

How did the researchers interpret the results?

The researchers list the problems relating to the use of herbal products as:

  • Lack of scientific evidence for safety or how well they work.
  • Lack of regulation to protect people from harmful effects on their health and finances.
  • Lack of quality control of manufacturing processes.
  • Public misinformation due to unethical marketing techniques and false advertisements.
  • Lack of knowledge about herb-drug interactions by patients and health care providers.
  • Under-reporting of adverse drug reactions.

They call for:

  • Better public and physician understanding of herbal products through health education.
  • Early detection and management of herbal toxicities.
  • Scientific scrutiny of the use of herbs and research on their safety and effectiveness.

The researchers conclude that the principles and standards of evidence for safety and efficacy of drugs used in conventional medicine should also apply to herbal and other complementary and alternative medicine products.


This review has looked at a serious topic using acceptable methods. There are several difficulties due to the fact they found little good quality research on the topic:

  • Most of the research into the harms from these drugs is from single case reports or case series. This is regarded as low-level evidence, because without a control group it is not possible to say for certain what caused the events and what the background rates of these incidents (such as bleeding) are in the general population.
  • There is no detail on how the researchers selected the articles or how many they found in their search. A fully systematic review would describe the number of studies identified by the search and the detailed methods of each study. As this report has not done this, the reader is unable to assess the overall quality of the study.

Many people have a false sense of security about these herbal products because they are seen as natural. But natural does not always mean safe. Anybody considering taking complementary or alternative medicine alongside their own prescribed medication are advised to discuss this with a doctor, nurse or pharmacist first.

NHS Attribution