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Can herbs help to treat cancer?


Cancer patients often use complementary therapies to improve emotional wellbeing, “boost” the immune system or reduce the side-effects of chemotherapy. One European-wide survey found that the use of herbs to treat cancer has tripled since the mid-1990s, with about one in eight cancer patients now using them.

A huge variety of herbs are recommended, including mistletoe, garlic, astragalus, and many multi-herb combinations such as Essiac and PC-SPES. Most have little data to demonstrate whether or not they are effective or safe, especially in combination with chemotherapy. Two remedies stand out as examples of the potential and the limitations of using herbs to treat cancer.


First used 80 years ago, European mistletoe (Viscum album) is the herb most often mentioned in relation to cancer. Several anti-cancer compounds have been found in its extracts. In the past 10 years, several controlled clinical trials have been published.

A 2010 review identified 26 randomised controlled trials, although only four were double-blinded. In most, patients received conventional cancer care along with mistletoe injections. The results for treatment of the cancer and patient survival were mixed. However, consistent benefits were found for quality of life, especially fatigue and sleep quality. Impact on chemotherapy side-effects was inconsistent. Purified active ingredients from mistletoe are currently being developed and tested.

PC-SPES is a remedy made from eight herbs used in traditional Chinese medicine for prostate problems. First marketed in 1996, it gained a reputation for treating advanced prostate cancer. Few other treatments are available for such cancers and life expectancy is short. Positive laboratory studies were followed by clinical studies reporting remission in almost all patients taking PC-SPES.

However, in 2001 patients noticed inconsistent results between different batches of PC-SPES and also reported bleeding problems. An independent analysis found variation in the active ingredients between batches, and also that some contained drugs, including warfarin (which inhibits blood coagulation). In 2002, the product was withdrawn from the market.

A British company is testing a new formulation (PC-SPES2). It claims it can ensure consistency between batches and prevent adulteration. However, these remain issues until regulations ensure that only herbal products made to the highest standards make it onto the market.


European mistletoe injections have few adverse effects and are relatively mild. Oral preparations are usually not recommended because of adverse effects. American mistletoe is a different species with more toxicity.

More generally, interactions can occur between herbs and chemotherapy drugs. For example, in 10 women with breast cancer taking docetaxol, the drug’s clearance from the body was reduced by garlic supplements. This highlights the potential for herbs to increase the risk of side effects. In other studies, cancer patients taking St John’s wort for mild depression had blood levels of their chemotherapy drugs reduced by one-third. This could reduce the chemotherapy’s effectiveness.


Treating cancer is challenging, especially in advanced stages when medical treatments are not effective. Plants have provided powerful drugs to treat the disease, such as vinca alkaloids and taxol. However, years of research are involved to identify how best to use these resources. On the other hand, cancer patients have fallen prey to unscrupulous producers of herbal remedies, as with the PC-SPES incident. Given the potential for any herb to interact with medicines, cancer patients should talk with their healthcare professionals about any herbal remedies they are considering.

Dónal OMathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University