What to avoid taking with selenium?

January 2, 2026 •

3 min read

While essential for health, high doses of selenium can be toxic, potentially leading to organ failure. It is therefore crucial to be aware of potential interactions with certain medications and other supplements to prevent side effects and serious health complications.

Quick Summary

To take selenium supplements safely, it is vital to know which drugs and other supplements can cause adverse interactions. Certain medications, including anticoagulants, chemotherapy drugs, and statins, may interact negatively. Individuals with specific health conditions like autoimmune diseases or hypothyroidism also need caution when supplementing.

Key Points

Blood Thinners: Avoid combining selenium with anticoagulant drugs like warfarin and antiplatelet drugs like aspirin, as this can increase the risk of bleeding.
Chemotherapy Drugs: Exercise caution, as selenium supplements can interfere with the effectiveness of some cancer medications, such as cisplatin.
High-Dose Caution: Regularly exceeding the 400 mcg daily upper limit can lead to selenium toxicity, causing serious side effects like hair loss and organ damage.
Autoimmune Conditions: Individuals with autoimmune diseases like lupus or rheumatoid arthritis should avoid selenium supplements, as they can potentially over-stimulate the immune system.
Thyroid Management: If you have an underactive thyroid and are iodine deficient, take selenium with iodine, as selenium alone could worsen hypothyroidism.
Brazil Nuts: Limit intake of Brazil nuts, as they are extremely high in selenium and can contribute to toxicity if eaten frequently.

Interactions with Medications

Anticoagulants and Antiplatelet Drugs

Selenium is known to have a blood-thinning effect, which can be dangerous when combined with anticoagulant and antiplatelet drugs. Taking these together increases the risk of bruising and bleeding.

Warfarin (Coumadin): Taking selenium with this medication can significantly increase its blood-thinning effects.
Aspirin and Clopidogrel (Plavix): These antiplatelet drugs can also cause an increased risk of bleeding when taken alongside selenium.

Chemotherapy Drugs

Some chemotherapy agents have known interactions with selenium. The relationship is complex, as some chemo treatments can deplete selenium, while supplementation can affect the drug's efficacy.

Cisplatin: This cancer drug can lower selenium levels in the body, yet supplemental selenium may interfere with how well the drug works.
Clozapine: This antipsychotic drug is also known to interact with selenium levels.

Cholesterol-Lowering Medications (Statins)

While not as severe as with anticoagulants, there is a moderate interaction risk involving cholesterol-lowering drugs, particularly when combined with other antioxidants.

Niacin + Simvastatin: A combination of niacin and simvastatin, taken with selenium and other antioxidants like Vitamin C and E, can decrease the beneficial effects on good cholesterol levels.

Sedative Medications (Barbiturates)

Selenium can reduce the speed at which the body breaks down sedatives. This can lead to an increase in their effects and potential side effects, which can be dangerous.

Immunosuppressants

For individuals with autoimmune disorders or organ transplants, the use of immunosuppressant medications is critical. Selenium's ability to stimulate the immune system could potentially counteract the effects of these vital drugs.

Potential Interactions with Other Supplements and Food

The Importance of Avoiding Excessive Intake

Even without medication interactions, some dietary choices require careful consideration to prevent selenium toxicity.

Brazil Nuts: These are a notoriously rich source of selenium, with just one nut containing a significant portion of the daily recommended intake. Consuming too many can quickly lead to toxic levels.
Alcohol and Unhealthy Foods: Limiting foods high in sugar, saturated fat, and sodium, as well as alcohol, is recommended as they can hinder selenium absorption.

Comparison of Intake Risks


Intake Source	Risk Level	Notable Considerations
Dietary Sources	Low to Moderate	Can be managed by moderating portion sizes, especially for high-concentration foods like Brazil nuts.
Standard Supplements	Moderate	Stick to recommended dosage (55 mcg/day for adults), as daily use can accumulate over time.
High-Dose Supplements	High	Use only under a doctor's supervision. The upper limit for adults is 400 mcg/day to avoid toxicity.
Specific Drug Combos	High	Dangerous interactions can occur with anticoagulants, chemotherapy, and immunosuppressants. Requires medical consultation.

What to Do to Take Selenium Safely

If you are on any medication or have health concerns, it is crucial to consult a healthcare provider before starting any new supplement, including selenium.

Best practices include:

Talk to Your Doctor: Discuss all current medications and supplements you take before adding selenium to your regimen. They can help you determine the right dosage and monitor for any adverse effects.
Monitor Your Intake: Track your selenium consumption from both food and supplements, especially from concentrated sources like Brazil nuts, to avoid exceeding the daily tolerable upper intake level of 400 mcg.
Consider Timing: To optimize absorption and minimize potential interactions, some sources suggest taking selenium with a meal. Splitting a higher dose may also help maintain steady levels and minimize side effects.

Conclusion

While selenium is a vital mineral, understanding potential drug and supplement interactions is key to safe supplementation. High doses or combinations with certain medications like blood thinners and chemotherapy drugs can lead to dangerous health complications. Always consult with a healthcare professional before starting or changing your supplement routine to ensure a balanced and safe approach to your health. For general dietary information on selenium, consider reviewing facts from authoritative sources like the National Institutes of Health.

Frequently Asked Questions

No, you should avoid taking selenium with blood-thinning medications like warfarin and aspirin, as it can increase the risk of excessive bleeding and bruising.

No, individuals with autoimmune diseases such as lupus, rheumatoid arthritis, or multiple sclerosis should avoid selenium supplements. Selenium can stimulate the immune system, potentially worsening these conditions.

While some chemotherapy drugs like cisplatin can lower selenium levels, supplementing selenium might also decrease the drug's effectiveness. Always consult your oncologist before combining them.

No, you should moderate your intake of Brazil nuts. They are a very high source of selenium and can easily cause you to exceed the safe upper limit, increasing the risk of toxicity.

Yes, taking selenium along with certain statins (like simvastatin) and other antioxidants may reduce the statin's beneficial effects on cholesterol levels.

Selenium toxicity, or selenosis, can occur from consistently high intake. Symptoms include hair loss, brittle nails, gastrointestinal issues, irritability, and a garlic-like odor on the breath.

Yes, you should stop taking selenium at least two weeks before a scheduled surgery. Its blood-thinning properties can increase the risk of bleeding.