This page is translated by Google and can contain errors. Go back to English.
Patient question

Doctor, can I take supplements?

Doctor, can I take supplements?

Patients often ask us, through our My Cancer Navigator service, “What supplements should I, or can I take?”. The most straightforward answer would be: “None!”. A balanced diet normally provides the body with the necessary nutrients. Extra supplements are not necessary in most circumstances. But unfortunately, not all diets are balanced and give the sufficient amount of required nutrients. Certainly, for people with cancer, this is a reason for concern.

Malnutrition is very common in cancer patients, as 20 to more than 70% are confronted with this problem (1). The explanation is simple: cancer can alter the metabolism of the body, reduce the appetite of patients, as well as change the nutrient uptake in the gastrointestinal tract, which increases the dietary needs for more proteins, carbohydrates, fats, vitamins, and minerals. In addition, malnutrition can also be caused by the side effects of a cancer treatment.

It goes without saying that malnourishment is pernicious for people with cancer and can lead to a higher toxicity of a cancer treatment and an overall worsening condition of the patient, making it more difficult for the patient to tolerate the treatment and lowering the quality of life.

Also, patients undergoing surgery often require higher amounts of micronutrients to enhance postoperative wound healing. Taken together, there could be many reasons why a cancer patient is considering food supplements.

Caution is required

Before buying food supplements, it is very important to understand the differences between a medicine, or a drug, and a supplement. Drugs need to be manufactured under Good Manufacturing Practices (GMP). This means that they are manufactured under carefully checked conditions and packaged with complete information on the best dosage routine and schedule. Supplements need to be manufactured according to the food regulation. This implies that possible contamination (with chemical, mineral, plant-based, bacterial, or animal toxins) needs to be checked and it must be ensured that there are strict hygiene procedures during the production process.

The main difference between drug and supplement regulation is that the end product for supplements is not monitored. The minimum and maximum tolerable content of the active ingredient(s) in the end product for supplements is not checked and can, consequently, not be guaranteed. For registered drugs, this validation is essential.

Moreover, there is no stability test verifying whether or not the supplement remains stable until the expiry date and/or at higher temperature/humidity, which is also obligatory for medicines.

Therefore, supplements bought from an unknown source or online, could be contaminated with germs, pesticides, organic toxins, toxic heavy metals, or residual solvents. They could also have more, less, or even none of the substance(s) mentioned in the product information. Some herbal supplements were even found to enclose prescription drugs. These product quality issues can have serious consequences for the health of consumers, especially for people with cancer receiving cancer treatment.

It is important to know that a pharmacist is held responsible for the supplements he/she sells, and that for supplements bought online and from other sources, the purchaser is solely responsible. It might be quite challenging to know whether or not a certain supplement is reliable. When buying supplements, one should keep in mind the following:

  • A trustable supplier will clearly display the contact information of the manufacturer of the supplement on the website, product packaging, or instructional leaflet.

  • The information about the content of the supplement must be clear. Never trust “secret” herbs or combinations thereof.

  • Never trust promises of cures. If something sounds too good to be true, such as so-called wonder drugs or supplements, it probably is.

Supplements don’t cure cancer

Although supplements might be useful in some cases, they are not a substitute for a cancer treatment. If a supplement sold over the internet claims to cure cancer, without exception this claim is false. If a product is able to alter the outcome of a disease, it is by definition a drug and needs to have a Marketing Authorisation issued by a competent authority, therefore be tested, and approved as such. The claims on food and herbal supplements are rarely backed up by rigorous scientific evidence.

Websites often report on promising cancer research but do not mention explicitly that research has been performed. A treatment should only be postulated to show promise once it has been tested in people, and not only on cancer cells, in a laboratory setting. If you read news reports about a spectacular cancer treatment, please first fully evaluate the published research findings to learn if and how correct, these study results were achieved.

Your doctor is your best partner

In any case please always inform your treating team about the supplements that you consider taking. Sometimes there can be a risk for interactions with the medication that you are receiving, and a well-intended, at first sight innocent, action may result in undesirable side effects. And be aware that some supplements might reduce the effectiveness of a chemotherapy or radiation treatment.

Your doctor and your treating team are best placed to evaluate the need for supplements. Quite often you can have specialised nutritional counselling in the cancer centre where you are treated.

Here’s what we do for you

Our information service My Cancer Navigator is there to help patients understand scientific findings, put them into context or critically evaluate possible quality concerns. About all cancer treatments, including supplements. Please reach out, we are here to help.


Klara Rombauts & Guy Buyens

Klara Rombauts (MSc) is Research Manager and HR Coordinator of the Anticancer Fund. In the role of research manager, she has been answering questions from patients since the inception of the ACF and is passionate about empowering patients with the right information. Previously, she worked as a researcher in the pharmaceutical industry.

Guy Buyens (MD) is Medical Director at the Anticancer Fund. His experience comes from the pharmaceutical industry (international clinical research in oncology) and biotechnology, but also from hospital management (CEO of a hospital).