What Supplements Not to Take With Selenium?

November 20, 2025 •

4 min read

While selenium is a crucial trace mineral with antioxidant properties, an estimated one billion people worldwide are deficient in zinc, a mineral that can negatively interact with selenium supplementation. Understanding what supplements not to take with selenium is essential for maximizing its benefits and avoiding adverse effects.

Quick Summary

Certain vitamins and minerals can interfere with selenium's absorption or function. Careful consideration is required, especially with zinc and high-dose vitamin C, to prevent reduced efficacy or unwanted side effects.

Key Points

Zinc and Selenium Compete for Absorption: High doses of zinc can inhibit selenium absorption, and vice versa. It is often recommended to separate the intake of these two minerals or use a balanced formula.
High-Dose Vitamin C Affects Inorganic Selenium: Taking high doses of vitamin C (ascorbic acid) at the same time as inorganic selenium (selenite) can reduce the selenium to an unabsorbable form, limiting its effectiveness.
Selenium Can Enhance Anticoagulant Effects: Due to its potential mild blood-thinning properties, selenium can increase the risk of bruising and bleeding when combined with anticoagulant and antiplatelet drugs like warfarin.
Interactions with Cholesterol and Immunosuppressant Drugs: Selenium may interfere with the effectiveness of niacin (when taken with statins) and can potentially lessen the effect of immunosuppressants.
Organic vs. Inorganic Selenium Matters: The form of selenium is important, as organic selenomethionine is generally better absorbed and less prone to interactions, though it carries a higher risk of toxicity at excessive doses due to its high bioavailability.

Navigating Supplement Interactions with Selenium

Selenium is an essential trace mineral involved in numerous critical bodily functions, including antioxidant defense, thyroid hormone metabolism, and immune function. When considering supplementation, however, it is important to be aware of potential interactions with other supplements and medications. Some supplements can hinder selenium absorption, while selenium itself can alter the effectiveness of other vitamins or prescription drugs. Awareness of these interactions is vital for ensuring both safety and the effectiveness of your health regimen.

Specific Supplement Interactions to Consider

Zinc and Selenium: A Complicated Relationship

One of the most notable interactions occurs between selenium and zinc. While both are important for a healthy immune system and overall cellular health, studies have shown an antagonistic relationship regarding absorption, especially when high doses are involved. A key finding in rat studies revealed that a high concentration of one mineral could decrease the absorption of the other. Specifically, higher levels of zinc were found to decrease selenium absorption in zinc-adequate subjects. In practice, this means taking large amounts of both minerals at the same time could compromise the bioavailability of one or both. A balanced dietary intake is generally preferred, or spacing out supplementation if taking high doses of each.

The Impact of High-Dose Vitamin C on Inorganic Selenium

The interaction between vitamin C (ascorbic acid) and selenium is nuanced and depends largely on the form of selenium taken. Research suggests that high doses of vitamin C can interfere with the absorption of inorganic selenium (like sodium selenite), potentially by reducing it to its elemental form, which the body cannot absorb effectively. This interaction is less of a concern with organic selenium (like selenomethionine), which is more readily absorbed by the body regardless. For those taking inorganic selenium supplements, it may be prudent to separate the dose from high-dose vitamin C intake. Taking both with meals can also help mitigate the interaction.

Other Notable Supplement and Drug Interactions

In addition to the zinc and vitamin C interactions, several other substances require caution when taken with selenium.

Niacin and Statins: Some studies indicate that taking a combination of niacin with cholesterol-lowering statin drugs alongside selenium and other antioxidants can decrease the effectiveness of the niacin and statin drugs in raising good cholesterol (HDL).
Anticoagulants and Blood Thinners: Selenium may have a mild blood-thinning effect. When combined with prescription anticoagulants like warfarin or antiplatelet drugs, it could increase the risk of bruising and bleeding. This is a particularly important consideration for anyone on blood-thinning medication.
Immunosuppressants: Selenium can stimulate the immune system. This could potentially interfere with the efficacy of immunosuppressant drugs used for autoimmune diseases or after an organ transplant.
Iron Supplements: Some studies have shown that high-dose iron supplementation can negatively affect the body’s selenium status, especially in individuals with low selenium levels. High iron doses have been shown to reduce plasma selenium levels.
Birth Control Pills: Oral contraceptives may affect blood levels of selenium, although the clinical significance of this interaction is not entirely clear.

Comparison of Common Supplement Interactions with Selenium


Supplement	Type of Interaction	Risk/Impact	Recommendation
Zinc	Absorption interference	Reduced bioavailability of one or both minerals.	Separate intake, consider a balanced multi-mineral supplement.
High-dose Vitamin C (with inorganic selenium)	Absorption interference	Reduction of inorganic selenium to an unusable form.	Avoid taking high doses of vitamin C and inorganic selenium at the same time.
Niacin (with Statins)	Efficacy reduction	Can decrease the effectiveness of niacin and statins in some cases.	Consult a doctor before combining; monitor cholesterol levels.
Anticoagulants	Increased side effects	Increased risk of bruising and bleeding.	High doses of selenium should be used with caution; consult a healthcare provider.
Iron	Absorption interference	High doses may decrease plasma selenium levels.	Consider separating intake, especially with inorganic selenium.
Immunosuppressants	Efficacy reduction	Can potentially counteract the effects of immunosuppressant medications.	Requires strict medical supervision; do not combine without consulting a doctor.

The Importance of Supplement Form

The form of selenium—organic versus inorganic—is a critical factor in understanding potential interactions. Organic forms like selenomethionine, found naturally in foods like Brazil nuts and supplemented in enriched yeast, are generally considered to be highly bioavailable and less susceptible to interference from other substances like vitamin C. The body absorbs organic selenium as if it were methionine, an amino acid, which can be stored in the body's protein pool. However, this higher absorption rate without regulation means there is a greater risk of toxicity if taking excessive amounts from supplements. Inorganic forms, such as sodium selenite and sodium selenate, are absorbed less efficiently and are more prone to specific interactions, such as with high-dose vitamin C.

Conclusion: A Personalized Approach to Supplementation

Understanding what supplements not to take with selenium is a vital part of safe and effective supplementation. Interactions with minerals like zinc, vitamins like C (in its inorganic form), and various medications can either reduce selenium's efficacy or amplify the risk of side effects. Because of the complexity and variations based on selenium form, dosage, and individual health status, the best practice is to consult with a qualified healthcare provider. They can help determine the right combination and dosage for your specific needs, ensuring your supplement regimen supports your health goals without unintended consequences. For more detailed information on specific drug interactions, it is advisable to consult reliable resources like the NIH Office of Dietary Supplements.

Frequently Asked Questions

It is generally not recommended to take high doses of zinc and selenium at the same time, as they can interfere with each other's absorption. For most people, a balanced multi-mineral supplement or separating the intake is a better approach.

High doses of vitamin C can interfere with the absorption of inorganic forms of selenium, such as sodium selenite, by converting it into a form the body cannot use. This is less of a concern with organic selenomethionine.

Yes, you should exercise caution. Since selenium may have mild blood-thinning effects, combining it with prescription anticoagulants like warfarin could increase the risk of bleeding. Always consult your doctor before combining them.

Yes, some evidence suggests that selenium, when combined with niacin and statin drugs, can reduce the effectiveness of those medications in raising good cholesterol (HDL). Discuss this with your healthcare provider.

Yes. Organic selenomethionine is more bioavailable and less prone to interference from other supplements like vitamin C. Inorganic forms like selenite are more likely to have their absorption affected by other nutrients.

Excessive selenium intake, especially from high-dose supplements, can lead to toxicity, with symptoms including bad breath (garlic odor), hair loss, fatigue, and nausea. The organic form has a higher risk of overdose due to unregulated absorption.

Individuals with autoimmune diseases, those on immunosuppressants, people taking blood-thinning medications, and those at high risk for skin cancer should be particularly cautious and consult a healthcare provider before starting selenium supplementation.