The ten most commonly asked about complementary medicines all interact with conventional treatments, potentially posing a threat to patient health and reaffirming the need for complementary or alternative therapies to be discussed between patients and their healthcare provider.

The new research, being presented on December 3rd at the Clinical Oncology Society of Australia's (COSA's) Annual Scientific Meeting, reveals the 10 most commonly inquired about complementary medicines at Melbourne's Peter MacCallum Cancer Centre all have predicted or actual drug interactions when taken with chemotherapy, radiation therapy or before surgery.

The research involved an audit of inquiries to the hospital's Medicines Information Centre from health providers and patients, over two years.

The 10 most commonly inquired about products or supplements (excluding vitamins and minerals) were: fish oil, turmeric, coenzyme Q10, milk thistle, green tea, ginger, lactobacillus, licorice, astragalus and reishi mushroom.

Lead researcher and Senior Pharmacist at Peter MacCallum's Medicines Information Centre, Sally Brooks, said while levels of these substances found in a healthy diet were unlikely to cause contraindications, larger amounts in complementary medicines could.

"These products may increase the effects of chemotherapy and put the patient at risk of toxicity, or decrease the efficacy of chemotherapy," Ms Brooks said. "Those that contain high levels of anti-oxidants may interfere with both chemotherapy and radiation therapy."

Ms Brooks said more research was needed. "Every cancer type is different and every individual case is different. What's safe for one person may not be for another. In the meantime, we need to raise public awareness of proven and potential risks."

COSA President, Associate Professor Sandro Porceddu, said patients could wrongly assume anything 'complementary' must 'complement' conventional cancer therapies and anything natural must be safe. "Although some complementary therapies and medicines may benefit patients, they can also be dangerous and undermine treatment," he said.

"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."