Taking selenium supplements does not keep thyroid hormone levels improved in people with Graves' disease beyond six months; after nine months, these levels return to what they were before treatment, even if supplementation continues.

Taking selenium supplements daily at 100–300 micrograms for six months may lower levels of antibodies targeting the thyroid-stimulating hormone receptor in adults with Graves' disease who are on antithyroid drugs, but this reduction does not last beyond nine months.

It is unclear whether selenium supplements help treat Graves' disease because studies have varied widely in how they gave selenium, did not measure patients' initial selenium levels, and used lab tests instead of actual health outcomes like disease remission.

Taking selenium supplements at 100–300 micrograms per day for 3 to 6 months may lead to a small rise in thyroid-stimulating hormone levels in adults with Graves' disease who are on antithyroid drugs, but this change does not continue after 6 months.

There is no clear evidence that taking selenium supplements improves key outcomes for people with Graves' disease, such as reducing relapses, improving quality of life, or easing eye symptoms.

In adults with Graves' disease taking antithyroid medication, taking selenium supplements at 100–300 μg per day for 3 to 6 months lowers levels of FT3 and FT4 hormones in the blood, but these reductions do not remain after 9 months of treatment.