Supplements During Cancer Treatment: What You Should Know

If you are going through cancer treatment, you may be wondering whether vitamins, minerals, herbs, medicinal mushrooms, or other supplements could help you feel better, support your nutritional status, or improve your ability to tolerate treatment.

You may also be hearing conflicting advice.

One person may tell you that supplements are essential during cancer treatment. Another may tell you to stop everything. Online, you can find claims that particular supplements can "boost immunity," "detoxify" the body, or even make cancer treatment work better.

The reality is more nuanced.

Supplements can have a role in supportive cancer care, but they are not automatically helpful—or harmful—simply because they are natural.

The appropriate approach depends on the specific supplement, the dose and formulation, your nutritional status, your cancer diagnosis, your treatment regimen, other medications, and what you are hoping to accomplish.

Why do people consider supplements during cancer treatment?

Cancer treatment can place new demands on the body and can sometimes make it more difficult to meet nutritional needs.

Changes in appetite, nausea, taste, bowel function, fatigue, or other treatment-related symptoms may make it harder to eat normally. Some people also enter treatment with existing nutrient deficiencies or dietary restrictions.

Others are interested in supplements because they want to:

• Correct a nutrient deficiency

• Support nutritional status

• Manage treatment-related symptoms

• Address a specific health concern

• Maintain strength and energy

• Support recovery and survivorship

• Continue supplements they were already taking before their diagnosis

These are all reasonable questions to bring to your healthcare team.

The challenge is determining which supplements are actually appropriate and useful in your particular situation.

Are supplements safe during cancer treatment?

There isn't a single answer.

Some supplements may be appropriate in certain circumstances, while others may interact with cancer treatments or other medications.

Research on interactions between dietary supplements and cancer therapies is also incomplete. The National Cancer Institute notes that supplements can potentially affect how cancer drugs are absorbed, metabolized, transported, or eliminated from the body.

This is one reason I don't recommend making decisions about supplements based solely on whether an ingredient is "natural."

A supplement can have a meaningful biological effect—which is part of why it may be useful—but that same effect can sometimes create an interaction.

Does this mean I should stop taking all my supplements?

Not necessarily.

This is where individualized assessment becomes important.

For some people, continuing a particular supplement may make sense. For others, temporarily stopping it may be appropriate. In some cases, a supplement may be changed to a different dose or formulation.

The answer can also change throughout the course of treatment.

For example, a supplement that may be reasonable during survivorship may require a different assessment during active chemotherapy, before surgery, or during another intensive treatment period.

Rather than assuming that every supplement is either safe or unsafe, I prefer to look at why you're taking it, what it contains, how much you're taking, and what treatment you're receiving.

What about vitamins and minerals?

Vitamins and minerals are an important area to consider because supplementation can sometimes be used to address a documented or suspected nutritional deficiency.

Examples may include:

• Vitamin D

• Vitamin B12

• Iron

• Folate

• Magnesium

• Other nutrients based on individual circumstances

When appropriate, laboratory testing can help determine whether a deficiency is present and can help guide supplementation.

For example, someone with low vitamin B12 or iron stores may have a clear reason to supplement. In other situations, testing may not be necessary or may not change the treatment plan.

This is different from automatically taking high doses of multiple vitamins "just in case."

The goal is to identify and address nutritional needs—not to create the highest possible nutrient intake.

What about antioxidants?

Antioxidants are one of the most complicated areas of the supplement conversation during cancer treatment.

Antioxidants include compounds such as vitamin C, vitamin E, carotenoids, polyphenols, and glutathione.

They are found naturally in many foods and are also available in concentrated supplement forms.

You may have heard that antioxidants are either essential during cancer treatment or that they should always be avoided.

Neither statement captures the full picture.

Some cancer treatments can involve oxidative processes, and there are theoretical concerns that high-dose antioxidant supplementation could interfere with the intended effects of certain therapies. At the same time, the research in humans is mixed and varies depending on the antioxidant, dose, cancer treatment, and clinical context. The NCI notes that there is insufficient information for many specific antioxidant supplements to determine whether they are safe and effective alongside standard cancer treatment.

This is an excellent example of why dose and context matter.

Eating a varied diet containing fruits and vegetables is not equivalent to taking a concentrated high-dose antioxidant supplement.

If you're considering a high-dose antioxidant supplement during active cancer treatment, it is worth discussing it with your oncology and integrative care team rather than making the decision based on general advice about "antioxidants."

What about herbs and botanical supplements?

Herbal medicine can be a useful component of integrative care, but herbs can also interact with medications.

Some botanicals can affect enzymes and transport proteins involved in how medications are processed in the body. This can potentially increase or decrease medication concentrations or alter their effects.

This is particularly relevant with cancer medications because many chemotherapy agents, targeted therapies, hormonal therapies, and other medications have specific metabolic pathways.

For example, St. John's wort is well known for its potential to alter drug metabolism and has been shown to interact with certain medications.

Other botanicals may influence blood clotting, blood pressure, blood glucose, immune function, or other physiological processes.

That doesn't mean that all herbs need to be avoided during cancer treatment.

It means they need to be evaluated individually and in the context of the treatment being received.

What about medicinal mushrooms?

Medicinal mushrooms are an especially interesting area of cancer research.

Mushrooms such as turkey tail, maitake, reishi, and shiitake have been investigated for their potential effects on immune function and other biological pathways relevant to cancer care.

Some mushroom-derived compounds have also been studied in clinical settings. However, research involving a particular mushroom, extract, or isolated compound does not necessarily mean that every commercially available mushroom supplement will have the same effects.

The preparation, extraction method, concentration, dose, and quality of the product can all matter.

This is an area where there is significant research interest, but also a need to distinguish promising research from established clinical benefit.

If you are interested in medicinal mushrooms during cancer treatment, the specific product and treatment context should be reviewed rather than assuming that a mushroom supplement is automatically appropriate.

What about supplements for cancer treatment side effects?

This is one of the areas where supplements may have a particularly practical role in supportive care.

Depending on the symptom, options may include nutritional strategies, lifestyle interventions, acupuncture, medications, or targeted supplements.

For example, ginger has been studied for nausea and may be considered in some situations.

Other supplements may be considered for specific nutritional deficiencies or symptoms when there is a reasonable evidence base and no significant interaction with the cancer treatment.

The important distinction is that the goal is symptom support, not treating the cancer itself.

A supplement should not be used as a substitute for an evidence-based treatment for the underlying cancer.

What about supplements that claim to "boost the immune system"?

This is an area where marketing language can be particularly misleading.

"Immune boosting" sounds appealing, especially during cancer treatment, but immune function is complex.

More immune activity isn't necessarily better in every situation.

For example, some cancer treatments—including immunotherapies—work by altering interactions between the immune system and cancer cells. That makes broad claims about "boosting immunity" particularly difficult to interpret without considering the specific treatment.

Rather than asking whether a supplement "boosts immunity," I prefer to ask:

What specific outcome are we trying to influence, and is there evidence that this intervention can help?

That is a much more clinically useful question.

What about taking supplements before chemotherapy or surgery?

Timing can matter.

Some supplements may affect bleeding, sedation, blood pressure, blood glucose, or medication metabolism. These considerations can become particularly important around surgery or certain procedures.

For this reason, your healthcare team should know about all supplements you are taking before a procedure.

Some cancer centres recommend stopping herbal products and dietary supplements before surgery or certain cancer treatments because of potential interactions. The exact timing should be individualized and follow the instructions of your treatment team.

This is another reason not to make abrupt changes based on general information online.

How I approach supplements during cancer treatment

When considering a supplement for someone with cancer, I look at several factors.

1. What are we trying to accomplish?

Is the goal to correct a deficiency, support nutrition, manage a symptom, or address another specific concern?

A clear clinical goal helps determine whether supplementation is worthwhile.

2. What does the evidence show?

I consider human clinical research where available, while also recognizing that evidence quality varies considerably between supplements.

3. What cancer treatment are you receiving?

A supplement that may be reasonable in one clinical context may not be appropriate in another.

Chemotherapy, targeted therapy, endocrine therapy, immunotherapy, radiation, and surgery all create different considerations.

4. What medications and supplements are you already taking?

Interactions can occur between supplements and cancer medications, but also between supplements themselves.

A complete medication and supplement list is therefore important.

5. What dose and formulation are you considering?

"Vitamin C" or "turkey tail" doesn't tell us enough.

The dose, form, extraction, concentration, and route of administration can substantially change the clinical question.

6. Can we monitor the outcome?

If a supplement is being used to address a measurable deficiency or symptom, we can sometimes monitor laboratory markers or symptoms to determine whether it is actually helping.

If we can't identify what we're hoping to accomplish, it becomes much harder to know whether a supplement is worth taking.

What about supplements after cancer treatment?

The conversation doesn't necessarily end when active treatment ends.

Survivorship can bring its own nutritional and health considerations, including changes in body composition, metabolic health, bone health, cardiovascular risk, fatigue, digestive symptoms, and other long-term concerns.

Some people may also continue supplements they started during treatment.

At this stage, it can be useful to reassess the supplement plan rather than continuing everything indefinitely.

A supplement that was useful for correcting a deficiency during treatment may no longer be necessary once that deficiency has been addressed. Conversely, a new nutritional or metabolic concern may emerge during survivorship.

Supplementation should evolve as your health and circumstances change.

Questions to ask before starting a supplement

If you're considering a new supplement during cancer treatment, some useful questions include:

• What am I taking this for?

• Is there evidence that it helps with that goal?

• Has it been studied with my particular cancer treatment?

• Could it affect how my medications work?

• What dose and formulation are appropriate?

• How long should I take it?

• Are there side effects I should watch for?

• Should I stop it before a procedure?

• How will we know whether it is helping?

You don't need to become an expert in every supplement before making a decision.

You just need to have enough information to make an informed decision with your healthcare team.

The bottom line

Supplements can be a valuable part of supportive cancer care—but they should be individualized, evidence-informed, and coordinated with your conventional cancer treatment.

There is no universal list of supplements that every person with cancer should take.

Sometimes supplementation is appropriate to correct a deficiency. Sometimes it may help address a specific symptom or nutritional need. Sometimes the best decision is to pause a supplement during a particular treatment or procedure. And sometimes there simply isn't enough evidence to justify taking it.

The goal isn't to avoid supplements out of fear, nor is it to take supplements because they are natural.

The goal is to determine what makes sense for you, at this point in your cancer journey.

Interested in individualized supplement guidance?

If you're navigating cancer treatment and wondering whether your current supplements are appropriate—or whether targeted nutritional supplementation may be helpful—an individualized consultation can help review your medications, supplements, nutritional status, treatment plan, and goals.

Book an Appointment →

Important note

This article is intended for general educational purposes and does not replace individualized medical advice. Supplements can interact with cancer treatments and other medications. If you are undergoing cancer treatment, preparing for surgery or a procedure, or taking prescription medications, discuss any new supplement with your oncology and healthcare team before starting it. Do not stop prescribed cancer treatment based on information in this article.