Avmacol Supplementation in Hypothyroidism on Levothyroxine

Direct Answer

Yes, taking Avmacol (selenium and zinc supplement) is safe for adults with hypothyroidism on levothyroxine, but it must be taken at least 4 hours apart from your levothyroxine dose to avoid absorption interference, and the evidence shows selenium provides minimal to no clinical benefit for most patients already on adequate thyroid hormone replacement. 1

Timing Requirements for Supplement Administration

Critical separation window:

Take Avmacol (or any selenium/zinc supplement) at least 4 hours apart from your levothyroxine dose 1
Levothyroxine should be taken on an empty stomach, 30-60 minutes before breakfast 1
Therefore, take Avmacol either mid-morning (if taking levothyroxine upon waking) or at bedtime (if taking levothyroxine in the morning) 1

Why this matters:

Minerals including zinc and selenium can bind to levothyroxine in the gastrointestinal tract, reducing its absorption 1
This interference can lead to inadequate thyroid hormone replacement despite appropriate dosing 1
The 4-hour separation ensures optimal absorption of both the thyroid medication and the supplements 1

Evidence on Selenium Supplementation in Hypothyroidism

For Patients Already on Levothyroxine (Your Situation)

The most recent and highest-quality evidence shows no benefit:

A 2024 multicenter randomized controlled trial of 412 patients with autoimmune thyroiditis on levothyroxine found that 200 μg selenium daily for 12 months provided no improvement in quality of life compared to placebo 2
Both selenium and placebo groups showed equal improvement in thyroid-related quality of life measures over 12 months 2
While selenium reduced TPO antibody levels compared to placebo (1995 vs 2344 kIU/L, p=0.016), this antibody reduction did not translate to any clinical benefit - it did not reduce levothyroxine dosage requirements or improve thyroid hormone ratios 2

Additional supporting evidence:

A 2016 study found that levothyroxine, but not selenium at any dose (83,166, or 249 μg), improved endothelial progenitor cell counts in hypothyroid patients 3
This suggests levothyroxine addresses the cardiovascular dysfunction of hypothyroidism, while selenium does not 3

For Subclinical Hypothyroidism (Not Yet on Levothyroxine)

Limited potential benefit in specific circumstances:

A 2016 study showed that 83 μg selenomethionine daily for 4 months restored euthyroidism in 31.3% of patients with subclinical hypothyroidism (TSH <10 mU/L) and autoimmune thyroiditis, compared to only 3.1% with placebo 4
However, this only applies to patients with mild subclinical hypothyroidism who are not yet on levothyroxine 4

Evidence on Zinc Supplementation

Mixed and limited evidence:

A 2015 study of 68 overweight/obese hypothyroid women found that 30 mg zinc gluconate daily for 12 weeks increased free T3 levels, and when combined with 200 μg selenium, also increased free T4 and decreased TSH 5
However, this study had significant limitations: small sample size, specific population (overweight/obese women), and unclear clinical significance of the biochemical changes 5
No high-quality evidence demonstrates that zinc supplementation improves clinical outcomes in hypothyroid patients already on adequate levothyroxine therapy 5

Practical Recommendation Algorithm

If you are already on levothyroxine with well-controlled TSH (0.5-4.5 mIU/L):

Selenium/zinc supplementation provides no proven clinical benefit 2
If you choose to take Avmacol anyway, separate it from levothyroxine by at least 4 hours 1
Monitor TSH every 6-12 months as usual 1
Do not expect improvement in hypothyroid symptoms from the supplement 2

If your TSH is not well-controlled on levothyroxine:

First priority: Optimize your levothyroxine dose through proper monitoring (TSH every 6-8 weeks during titration) 1
Ensure proper levothyroxine administration: empty stomach, 30-60 minutes before food, separated from other medications/supplements by 4 hours 1
Only after achieving optimal levothyroxine dosing should you consider whether supplements might provide marginal additional benefit 1

If you have subclinical hypothyroidism and are not yet on levothyroxine:

If TSH >10 mU/L: Start levothyroxine, not selenium 1
If TSH 4.5-10 mU/L with positive TPO antibodies and symptoms: Consider a trial of selenium (83 μg selenomethionine daily) for 4 months before starting levothyroxine 4
Recheck TSH after 4 months to assess response 4

Critical Safety Considerations

Avoid overtreatment risks:

Approximately 25% of patients on levothyroxine are unintentionally maintained on doses that suppress TSH, increasing risks for atrial fibrillation, osteoporosis, and cardiac complications 1
Adding supplements that might alter thyroid hormone levels could complicate dose management 1
Monitor TSH 6-8 weeks after starting any new supplement to ensure your levothyroxine dose remains appropriate 1

Selenium supplementation did reduce antibody levels:

While the 2024 trial showed selenium reduced TPO antibodies by approximately 15% compared to placebo, this did not improve symptoms, reduce medication needs, or provide any measurable clinical benefit 2
Lower antibody levels without clinical improvement represent a biochemical change of no practical significance 2

Common Pitfalls to Avoid

Do not take Avmacol with or near your levothyroxine dose - this will reduce levothyroxine absorption and potentially lead to inadequate thyroid hormone replacement 1
Do not expect symptom improvement from selenium/zinc if you are already on adequate levothyroxine - the 2024 evidence clearly shows no benefit 2
Do not use selenium as a substitute for levothyroxine in overt hypothyroidism - levothyroxine is the only proven effective treatment 1, 3
Do not assume lower antibody levels mean better outcomes - the 2024 trial proved this assumption wrong 2

Is it safe for an adult with hypothyroidism on levothyroxine to take Avmacol (selenium and zinc supplement) and should it be taken at a different time than the levothyroxine?

Help us tailor your experience