Experts are urging all patients undergoing chemotherapy treatment to inform their doctor if they are taking any kind of herbal supplement.

According to US researchers, there is increasing evidence that commonly used products, such as herbal tea, cumin and turmeric, can weaken or intensify the effects of drugs used during chemotherapy treatment.

They insist that in some cases, there may even be a lethal reaction.

"With the growth of the internet, patients have better access to information about alternative products and often turn to dietary and herbal supplements to treat their illness because they think they're natural and safe. What people don't realise is that supplements are more than just vitamins and can counteract medical therapies if not taken appropriately," explained lead researcher, Dr June McKoy, of Northwestern Memorial Hospital.

She called on patients to always inform their doctors about any medications, vitamins or supplements they are taking, in order to avoid any potential interaction.

Dr McKoy explained that herbal supplements can react with chemotherapy drugs in a number of ways. For example, some can ‘interfere with the metabolism of the drugs, making them less effective'.

"Other herbs such as long-term use of garlic may increase the risk of bleeding during surgery. While culinary herbs used in small quantities for flavoring are generally safe, consuming large amounts for prolonged periods of time may have a negative effect on the body when going through chemotherapy," she said.

Dr McKoy pointed to recent research which found that as many as half of chemotherapy patients did not inform their doctors if they were taking any kind of alternative or complementary medicines.

"Some believe it's not important, while others are uncomfortable admitting they are pursuing alternative therapies. The truth is, integrative approaches, such as massage and acupuncture, can be beneficial for cancer patients, but it's important to take these approaches at the right time and under the supervision of your doctor," she insisted.

She called on patients undergoing chemotherapy to stop taking herbal supplements until more information is known about potential interactions.

"Patients should bring in labels and bottles to their appointments. This can help the doctor calibrate drug dosage with other supplements in mind in order to prevent toxicities," Dr McKoy added.

Details of these findings were presented at a recent meeting of the American Society of Clinical Oncology.