Who Should Not Take Supplements? Key Health Considerations

October 9, 2025 •

4 min read

According to the National Institutes of Health, some supplements contain active ingredients with strong effects on the body, making it crucial to know who should not take supplements before starting a new regimen. In certain situations, from pre-existing health conditions to drug interactions, taking a seemingly harmless pill can lead to adverse effects, ranging from mild side effects to severe organ damage.

Quick Summary

This article outlines critical health considerations for individuals who should avoid dietary supplements. It covers how certain medical conditions, medications, and life stages like pregnancy can create serious risks, detailing specific interactions and potential negative consequences without professional guidance.

Key Points

Pre-existing Medical Conditions: People with kidney or liver disease should avoid certain supplements like high-dose potassium, magnesium, and specific herbs to prevent dangerous accumulation and toxicity.
Drug Interactions: Dietary supplements can interfere with prescription medications, such as St. John's wort decreasing the effectiveness of antidepressants and warfarin being affected by vitamin K.
Pregnancy and Nursing: Pregnant women should avoid high-dose vitamin A and many herbal supplements due to the risk of birth defects and lack of safety testing.
Risk of Over-supplementation (Megadosing): Taking too much of a supplement, especially fat-soluble vitamins like A and D, can lead to serious toxicity, liver damage, and other adverse effects.
Special Populations: Children, older adults, and individuals undergoing surgery should only take supplements under the guidance of a healthcare provider due to unique metabolic rates and potential complications.
Herbal Supplement Risks: Just because a supplement is 'natural' does not mean it is safe; many herbs have powerful effects and can cause organ damage or interact with medications.
Consult a Professional: The most critical step before taking any supplement is to consult a doctor, pharmacist, or registered dietitian to assess individual risk and need.

Supplements and Pre-existing Medical Conditions

For individuals with pre-existing medical conditions, supplements are not always a safe option. The body's ability to process and absorb nutrients can be compromised, and adding extra substances may worsen the condition or create new health issues.

Kidney and Liver Disease

Individuals with kidney disease must be extremely cautious with supplements, as impaired kidneys struggle to filter waste and process certain minerals. High doses of potassium, magnesium, and phosphorus from supplements can accumulate to dangerous levels, leading to heart rhythm problems or calcification. Creatine, a popular supplement for muscle growth, can also put extra stress on the kidneys and interfere with creatinine level readings.

Similarly, the liver is responsible for metabolizing supplements, and long-term overuse or high doses can cause liver injury. Herbal supplements like green tea extract, black cohosh, and kava have been linked to liver toxicity. Patients with existing liver disease or abnormal liver tests should avoid supplements containing high doses of retinol, iron, and manganese. The liver's reaction to supplements can also vary based on genetics, other medications, and individual susceptibility.

Cancer Patients and Survivors

For those undergoing cancer treatment, particularly chemotherapy, supplements can pose a significant risk. Antioxidants like vitamins C and E might interfere with chemotherapy's effectiveness by protecting cancer cells. High doses of beta-carotene have been linked to increased cancer risk in smokers and those exposed to asbestos. Cancer patients should never take supplements without explicit approval from their oncologist, especially during active treatment.

Heart Conditions and Hemochromatosis

Patients who have experienced a heart attack should be wary of beta-carotene supplements, while those with vascular diseases should be cautious with high doses of calcium. Individuals with hemochromatosis, an iron storage disorder, must avoid iron supplements and be careful with high-dose vitamin C, which can increase iron absorption.

Supplement and Medication Interactions

One of the most dangerous aspects of supplements is their potential to interact harmfully with prescription and over-the-counter medications. These interactions can alter a drug's effectiveness or increase its toxicity.

Anticoagulants and Blood Thinners

Supplements that thin the blood, such as vitamin E and ginkgo biloba, can increase the risk of bleeding or stroke when taken with prescription blood thinners like warfarin. Vitamin K, which helps blood clot, can have the opposite effect and reduce warfarin's effectiveness.

Antidepressants and Transplant Drugs

St. John's wort, a popular herbal supplement for mood disorders, can speed up the metabolism of many medications, including antidepressants, birth control pills, and drugs used by transplant recipients. This can cause serious consequences, including organ rejection in transplant patients.

Who Should Not Take Supplements: Special Populations and Megadosing

Pregnancy and Nursing

Pregnant and nursing women should exercise extreme caution. High doses of certain supplements, particularly vitamin A (retinol), can cause birth defects. While a prenatal supplement is often recommended, any additional supplements beyond that should be discussed with a doctor, as many have not been well-tested for safety during pregnancy and breastfeeding.

Children

Children's metabolisms are different from adults, and they process substances at different rates, increasing the risk of adverse reactions when taking supplements. Unsupervised ingestion of vitamins by young children can cause allergic reactions and digestive symptoms. Supplements should only be given to children under the supervision of a healthcare provider.

The Dangers of Megadosing

Megadosing, or taking excessively high amounts of supplements, can lead to serious health problems, even with seemingly benign nutrients. For example, too much vitamin A can cause liver damage and reduced bone strength, while excess iron can cause nausea and damage the liver. Fat-soluble vitamins (A, D, E, K) are particularly risky because they accumulate in the body's fatty tissues and liver, leading to toxicity.

Comparison of Supplement Risks by Health Factor


Health Factor	Key Supplements to Avoid/Use with Caution	Reason for Caution
Kidney Disease	High-dose potassium, magnesium, phosphorus, creatine, Vitamin C (>2000mg), licorice root	Risk of nutrient buildup, heart problems, kidney stones, overworking kidneys
Liver Disease	High-dose retinol (Vitamin A), iron, manganese, kava, green tea extract, black cohosh	Potential for liver injury, toxicity, and worsening pre-existing liver conditions
Anticoagulant Medication (e.g., Warfarin)	Vitamin K, Vitamin E, Ginkgo biloba, CoQ10	Can interfere with medication, increasing risk of bleeding or clotting
Antidepressant Medication	St. John's Wort	Can reduce the effectiveness of medications and cause serious side effects
Pregnancy	High-dose retinol (Vitamin A), black cohosh, dong quai, goldenseal, unapproved herbs	High doses of some vitamins can cause birth defects; many herbs lack safety data
Smoking/Former Smoking	Beta-carotene	High-dose supplementation has been linked to increased lung cancer risk

Conclusion

While supplements offer potential benefits for some, they are not universally safe. Individuals with underlying medical conditions, those taking medication, and special populations like pregnant women and children must exercise extreme caution. Consulting a healthcare professional before starting any new supplement is the single most important step to prevent dangerous drug interactions, nutrient toxicity, and other serious health complications. A balanced, whole-food diet remains the safest and most effective way for most people to meet their nutritional needs. For specific deficiencies or needs, a doctor can provide guidance on safe and appropriate supplementation, but the notion that 'natural' equals 'safe' is a dangerous misconception that can have life-altering consequences.

For more detailed information, the National Institutes of Health Office of Dietary Supplements provides extensive resources on supplement safety and potential risks.

Frequently Asked Questions

Yes, supplements can cause liver damage, especially when taken in high doses or if you have pre-existing liver conditions. Some herbal supplements, such as kava and green tea extract, have been specifically linked to liver toxicity.

Pregnant women should be cautious and only take supplements under a doctor's supervision. High doses of certain vitamins, like Vitamin A (retinol), are known to cause birth defects and should be avoided.

If you take blood thinners like warfarin, you should avoid supplements such as vitamin K, ginkgo biloba, and vitamin E, as they can interfere with the medication and increase the risk of bleeding or clotting.

No, many supplements are unsafe for people with kidney disease. High levels of potassium, magnesium, and phosphorus can be dangerous due to the kidneys' reduced ability to filter them. Creatine can also stress the kidneys.

It is not always safe. You should discuss all supplements, including multivitamins, with your healthcare provider. Supplements can alter how your body absorbs and metabolizes medication, making it more or less effective.

Taking too many supplements, known as megadosing, can lead to nutrient toxicity. Symptoms range from gastrointestinal distress to more severe issues like liver damage, bone pain, and heart palpitations, especially with fat-soluble vitamins (A, D, E, K).

Yes, herbal supplements can and often do interact with prescription drugs. St. John's wort is a well-known example that can reduce the effectiveness of many medications, including antidepressants and birth control pills.