Personal Health Navigator

How herbal remedies can jeopardize cancer treatment

woman holding pills
Written by Paul Taylor

Question: My sister has been diagnosed with breast cancer. She has always been a big believer in alternative medicine and is determined to keep taking her herbal supplements. She feels she is hedging her bets by combining conventional treatments with alternative therapies. But is this a safe approach?

Answer: Before your sister proceeds with her plan, she should at least tell her health-care providers what she is doing.

A wide range of supplements can potentially interact with conventional cancer treatments and reduce the chances they will work successfully or increase the risk of side effects.

One of the first things she will likely be told is that some herbal remedies – such as black cohosh and dong quai – have hormone-like properties.

That’s a concern because hormones sometimes act like jet fuel, accelerating the multiplication of cancer cells.  For instance, estrogen will stimulate certain types of breast cancer, while testosterone will spur on some prostate tumours.

“We would be worried about any alternative medicine that might cause the cancer to grow,” says Carlo De Angelis, an oncology pharmacist at Sunnybrook Health Sciences Centre in Toronto.

Supplements might also hamper some cancer treatments including chemotherapies that rely on an “oxidative mechanism.” This type of chemo produces free radicals – molecules that can interfere with the function of cancer cells and stop or slow their growth.

High doses of antioxidant supplements – such as vitamin C and E – are thought to counteract this chemo effect by neutralizing and eliminating free radicals.  “If there are fewer free radicals around, then you might reduce the effectiveness of the anti-cancer medication,” says De Angelis.

Furthermore, supplements may adversely affect treatment by altering how long drugs remain in the body. Usually, medications are metabolized – or broken down – by enzymes at a fairly predictable rate.  Some supplements, however, can affect this process so that a drug is present in the body for either a shorter or longer period than would normally be the case. If the time is cut short, then the drug may be less likely to produce its maximum benefit.   Or, if the timing is prolonged, the patient may suffer more side effects.

But possibly the biggest challenge posed by an alternative therapy is that you can’t always be sure what you are getting.

Herbal remedies and supplements don’t go through the same approval and regulatory process as prescription and over-the-counter medications.

As a result, there can be significant variations in quality and potency from one product to the next – and some of them may contain impurities. “That adds an extra layer of uncertainty,” says Mark Pasetka, an oncology pharmacist at Sunnybrook.

So, there are lots of reasons for caution. In the past, health-care providers generally tried to discourage cancer patients from using certain complementary or alternative medicines.

But that approach is gradually changing.  “The truth is that they are going to do it anyways,” says De Angelis.  He is quick to add that patients have a right to do as they see fit.

De Angelis says it’s now fairly common for doctors and pharmacists to ask patients if they are using any alternative therapies.  If they are taking supplements or other remedies, “we try to find a way to do it safely,” says De Angelis. That could mean carefully timing the different treatments so they don’t overlap and interact with the each other. Sometimes, though, that’s not always possible.

Pasetka says he is not surprised patients are tempted by alternative therapies. After all, countless cancer “cures” can be readily found on the Internet and well-meaning family and friends often suggest things to try.  But it’s not necessarily easy to evaluate all the competing claims.

For that reason, it’s critically important for health-care providers to encourage an “open dialogue” with patients “so they can make informed decisions based on risks and benefits,” says Scott Gavura, a pharmacist and director of drug reimbursement programs at Cancer Care Ontario.

One question that’s coming up with increasing frequency is whether marijuana can help cancer patients. Gavura says there are no clinical studies showing that cannabis can actually fight cancer. But there is some evidence suggesting it might provide symptom relief.

It may, for example, help ease pain or minimize the nausea from chemotherapy. The evidence, though, is still pretty sketchy.  And, when it comes to treating nausea, various conventional drugs may provide better results than marijuana. “At this point, there is no reason to go to cannabis without first trying the other medications,” say De Angelis.

Even so, the patient’s preference should prevail. As Pasetka puts it: “at the end of the day, it’s the patient’s decision.

About the author

Paul Taylor

Paul Taylor retired from his role as Sunnybrook's Patient Navigation Advisor in 2020. From 2013 to 2020, he wrote a regular column in which he provided advice and answered questions from patients and their families. Follow Paul on Twitter @epaultaylor