Common complementary therapies found to have serious drug interactions or reduce the effectiveness of chemotherapy or radiation treatment
The complementary therapies that cancer patients most commonly mention to doctors all potentially jeopardise the effectiveness of conventional treatments such as radiation, chemotherapy and surgery, an audit has found.
The research was presented at the Clinical Oncology Society of Australia (Cosa) annual scientific meeting on Wednesday, and was based on an audit of 462 patient enquiries about alternative therapies received by the Peter MacCallum Cancer Centre in Melbourne.
Excluding vitamins and minerals, cancer patients were most interested in fish oil, turmeric, coenzyme Q10, milk thistle, green tea, ginger, lactobacillus, licorice, astragalus and reishi mushroom as additional treatments.
All have predicted or known drug interactions when taken with evidence-based cancer treatments.
The lead researcher of the study and a senior pharmacist at the centre, Sally Brooks, said while the substances were unlikely to cause problems when consumed as part of a healthy diet, complementary medicines contained larger and potentially harmful amounts.
"These products may increase the effects of chemotherapy and put the patient at risk of toxicity, or decrease the efficacy of chemotherapy," Brooks said.
"Those that contain high levels of antioxidants may interfere with both chemotherapy and radiation therapy."
The president of Cosa, Associate Professor Sandro Porceddu, said patients could wrongly assume anything tagged "complementary" must complement conventional cancer therapies, and anything natural must be safe.
"Until we know more, it's best to err on the side of caution and for patients to discuss with their healthcare provider any complementary or alternative therapies they are using or considering using, in order to minimise risk," he said.
The Cosa statement on use of complementary and alternative therapies says patients may also face substantial costs by using complementary and alternative therapies at a time when they may be under financial stress due to taking leave from work and paying for standard treatments.
Cancer patients might also feel pressure from friends and family to use alternative therapies and could experience guilt if they were not successful, the statement says. Using unproven treatments might also disqualify patients from participating in clinical trials of new drugs, making open discussions between doctors and patients essential.
But Dr Ken Harvey, from Monash University's school of public health and preventative medicine in Melbourne, said: "Regrettably, patients often don't tell and doctors often don't ask patients".
"The key message is that complementary and alternative medicine usage is high in the community, not just in oncology patients, and its use is out of all proportion to the limited evidence available to support the efficacy of some of it," he said.
A woman looks through complementary medicines in a pharmacy. Cancer patients were most interested in fish oil, turmeric, coenzyme Q10, milk thistle, green tea, ginger, lactobacillus, licorice, astragalus and reishi mushroom, according to the audit. Photograph: Alamy