Understanding if You Can Take Levothyroxine and Selenium Together

October 9, 2025 •

4 min read

According to the National Institutes of Health, the thyroid contains the highest concentration of selenium per gram of tissue in the body, highlighting its critical role in thyroid function. For individuals on prescription thyroid hormone, a common question is: can I take levothyroxine and selenium together? The answer is generally yes, but proper timing is essential to avoid interfering with the medication's absorption.

Quick Summary

It is generally safe to take levothyroxine and selenium, provided they are taken at separate times to prevent absorption issues. Separating doses by at least four hours is recommended. Selenium offers potential benefits for thyroid health, particularly in autoimmune conditions like Hashimoto's, by helping to reduce antibody levels, though it is not a replacement for medication.

Key Points

Timing is crucial: To prevent absorption interference, take levothyroxine at least four hours apart from selenium supplements.
Selenium supports thyroid function: The mineral is essential for producing and converting thyroid hormones and protecting the gland from oxidative stress.
Combination may benefit Hashimoto's: Some studies indicate that combining levothyroxine with selenium can help reduce thyroid antibody levels in people with Hashimoto's.
Consult a doctor first: Always speak with a healthcare provider before adding a selenium supplement to your routine to determine if it's necessary and safe for you.
Beware of dosage: High doses of selenium can be toxic (selenosis); do not exceed 400 mcg per day.
Not a replacement for medication: Selenium is a supplement and should not be used as a replacement for prescription levothyroxine, which treats hypothyroidism.

The Importance of Separating Doses

While there is no major interaction between the substances themselves, the timing of your dose is critical to ensure your body properly absorbs levothyroxine. Thyroid hormone absorption can be hindered by various foods and other supplements, including minerals like selenium. For this reason, medical professionals recommend separating the administration of thyroid medication from other supplements and foods by several hours.

To ensure optimal absorption, the standard practice is to take levothyroxine on an empty stomach, typically in the morning, and wait at least 4 hours before taking any other medications or supplements, including selenium. For those who take their levothyroxine at bedtime, it should be taken at least 2 hours after the last meal. This consistent schedule helps maintain stable blood hormone levels, which is key for effective treatment.

The Role of Selenium in Thyroid Health

Selenium is a trace mineral that is essential for proper thyroid function, and its influence extends to several critical processes.

Thyroid hormone production: Selenium is a component of selenoproteins, which are necessary for the synthesis of thyroid hormones.
Conversion of T4 to T3: Selenodeiodinase enzymes, which require selenium, play a vital role in converting the less active T4 hormone to the more active T3 hormone.
Protection against oxidative stress: The process of producing thyroid hormones generates reactive oxygen species. Selenium, through its antioxidant properties, helps protect the thyroid gland from oxidative damage.
Immune modulation: In autoimmune thyroid diseases like Hashimoto's, selenium's anti-inflammatory and immune-modulating effects can be beneficial.

Combining Levothyroxine and Selenium: Potential Benefits for Hashimoto's

For people with Hashimoto's thyroiditis, the combination of levothyroxine and selenium has been the subject of numerous studies.

Reduction in thyroid antibodies: Several studies, including a meta-analysis published in Thyroid, have shown that selenium supplementation can significantly reduce levels of thyroid peroxidase antibodies (TPOAb) in patients with chronic autoimmune thyroiditis.
Improved thyroid structure: Some evidence suggests that selenium supplementation can also lead to improvements in thyroid ultrasound structure.
Improved quality of life: While some studies report improved well-being, the evidence for a direct effect on thyroid function parameters (TSH, T4, T3) in combination therapy can be mixed and requires more research.

Despite these promising results, it's crucial to understand that selenium is a supplement, not a cure, and should never replace prescribed thyroid medication. The European and American thyroid associations have noted that while selenium can be beneficial, the evidence is still inconclusive and does not currently justify routine recommendations for all Hashimoto's patients. The potential benefits may be most relevant for individuals with an existing selenium deficiency.

Safe Supplementation and Potential Risks

Before starting any new supplement, including selenium, it is essential to consult a healthcare provider. They can help determine if supplementation is appropriate, especially considering factors like your baseline selenium status.

High doses of selenium can lead to toxicity, a condition known as selenosis. Symptoms of selenosis can include hair loss, brittle nails, nausea, fatigue, and nerve damage. The tolerable upper intake level for selenium is 400 mcg per day.

It is important to remember that supplements are not regulated by the FDA in the same way as prescription drugs. Therefore, quality can vary. Relying on reputable brands and discussing the specific product with your doctor or pharmacist is always recommended.

Comparison Table: Levothyroxine vs. Selenium


Feature	Levothyroxine	Selenium
Primary Purpose	Synthetic thyroid hormone replacement to treat hypothyroidism.	Essential trace mineral that supports thyroid hormone production and acts as an antioxidant.
Administration Timing	Take on an empty stomach, at least 30-60 minutes before food and at least 4 hours apart from most supplements.	Take at a separate time from levothyroxine (at least 4 hours apart) to prevent absorption interference.
Availability	Prescription medication.	Dietary supplement and found naturally in foods like Brazil nuts, seafood, and eggs.
Clinical Evidence	Standard, well-established treatment for hypothyroidism.	Evidence supports potential benefits for autoimmune thyroiditis (Hashimoto's), but not a replacement for medication.
Risk	Side effects typically related to dosage issues. Consult your doctor if symptoms of hyper- or hypothyroidism arise.	High doses can cause toxicity (selenosis), leading to symptoms like hair loss and nail changes.

Conclusion

For individuals with hypothyroidism, especially those with autoimmune thyroiditis like Hashimoto's, taking levothyroxine and selenium together is possible and may offer added benefits, particularly regarding a reduction in antibody levels. The key to safe co-administration is timing: always take levothyroxine and selenium at least four hours apart to ensure the medication's full absorption. It is imperative to consult a healthcare provider before initiating any new supplement, as they can assess your specific needs, check for a deficiency, and help determine if supplementation is appropriate for you. Given that scientific evidence on selenium's precise clinical role is still evolving, a cautious, evidence-based approach under medical supervision is the safest path forward.

For more information on the evolving research surrounding selenium's role in thyroid health, you can refer to systematic reviews and meta-analyses, such as Selenium and thyroid diseases published by the National Institutes of Health.

Frequently Asked Questions

To avoid interactions, take levothyroxine on an empty stomach in the morning, at least 30-60 minutes before breakfast, and take your selenium supplement at least 4 hours later.

No, selenium cannot replace levothyroxine. Levothyroxine is a synthetic thyroid hormone replacement for hypothyroidism, while selenium is a mineral that supports thyroid function. Never stop or change your medication without consulting your doctor.

Selenium plays a key role in protecting the thyroid from oxidative damage and can help regulate the immune system. Some studies show that selenium supplementation can significantly reduce thyroid antibody levels (TPOAb) in people with autoimmune thyroiditis, or Hashimoto's.

Taking levothyroxine and selenium at the same time can interfere with the absorption of the levothyroxine medication, potentially reducing its effectiveness. This can lead to unstable thyroid hormone levels.

The ideal dosage should be determined by a healthcare provider, especially if you have a known deficiency. High doses (over 400 mcg) can be toxic and should be avoided.

Yes, excessive selenium intake can lead to a condition called selenosis. Symptoms include hair loss, brittle nails, nausea, fatigue, and nerve damage.

Yes, it is highly recommended to speak with your healthcare provider about getting your selenium levels tested before starting a supplement. They can determine if you have a deficiency and help find if supplementation is appropriate.