Can I Take Vitamins or Supplements During Chemo?

NCI's instruction here is unusually firm. Tell your doctor if you are taking any dietary supplements, even vitamins, no matter how safe you think they are. It adds: this is very important.

The practical version is to make a list before your next appointment and take it with you. Include the occasional things — the sleep gummies, the turmeric capsule someone gave you, the powder in the kitchen cupboard. NCI says to put over-the-counter and prescription medicines on the same list.

Nobody is going to tell you off. Your team simply cannot check for a problem they do not know exists.

NCI puts this under a heading of its own: natural does not mean safe.

Its warning is that herbal supplements may be harmful when taken by themselves, with other substances, or in large doses. All three routes matter. A product can be fine alone and a problem alongside a cancer drug. It can be fine at a small dose and harmful at a large one.

The word "natural" tells you where an ingredient came from. It tells you nothing about what it does in a body that is also processing chemotherapy.

Rather than leave this abstract, NCI names two products.

St. John's wort. Taken by some people for depression. NCI says it may cause certain cancer drugs not to work as well as they should. That is the outcome nobody wants: treatment quietly underperforming while everything looks fine.

Kava kava. Used for stress and anxiety. NCI says some studies have shown it may cause liver damage.

Neither is exotic. Both sit on ordinary store shelves.

This is the structural point, and the reason a supplement deserves the same care as a prescription.

NCI notes that these products do not have to be approved by the Food and Drug Administration before being sold to the public, and that no prescription is needed to buy them. Its conclusion is blunt: it is up to you to decide what is best for you.

An advertisement saying something has been used for years is not evidence, as NCI points out. That matters more once the product is combined with your medicines.

It is worth stating what the evidence does not show, because a lot of marketing implies otherwise.

NCI's wording: there are no studies that prove that any special diet, food, vitamin, mineral, dietary supplement, herb, or combination of these can slow cancer, cure it, or keep it from coming back. It follows straight on with the risk — some of these products can cause other problems by changing how your cancer treatment works.

So the trade is a real downside against an unproven upside. That is a statement about supplements taken as cancer treatment. It is not about a vitamin your team has prescribed to correct a shortage found on a blood test, a nutrition drink for weight loss, or a product you are taking as part of a trial. Those are different situations, covered next.

None of this means every supplement is off limits. Some are recommended.

NCI's nutrition guidance suggests nutrition supplement drinks, naming products such as Ensure or Boost, for people struggling to eat enough. A team may also prescribe a specific vitamin to correct a shortage found on a blood test.

The difference is that those decisions come from your team, based on your results, rather than from a shelf.

The pharmacist at your cancer center is often the fastest route to a real answer.

• Are the supplements I already take safe to continue?
• Could any of them affect how my treatment works?
• Is there anything you want me to stop — and is it something to stop today, or before the next cycle?
• Should I keep taking the things you have already prescribed me, and is there anything I should not stop on my own?
• Should I be taking anything, based on my blood results?
• Can I check new products with you before I buy them?

Bring the bottles if you can. Labels list ingredients that a product name does not.

This is general information. Your care team's specific instructions for your treatment always take priority.

• NCI — Complementary and Alternative Medicine
• NCI — Nutrition in Cancer Care