Bipolar Meds Not Working? Get Your Thyroid Checked!
A low thyroid hormone level can prevent mood medications from being effective.
Updated February 26, 2025 | Reviewed by Lybi Ma
The thyroid is a butterfly-shaped gland located at the front of the neck just below the Adam’s apple. It releases hormones into the bloodstream that play a vital role in the body’s energy regulation. Too little thyroid gland activity, called hypothyroidism, leads to sluggishness and weight gain. Too much, called hyperthyroidism, leads to metabolic overdrive—rapid pulse, nervous energy, and anxiety . While the precise role of thyroid hormones in mood regulation remains unclear, it’s known for sure that normal thyroid functioning is essential for mood disorder treatments to be effective. If a person’s mood doesn’t respond to the usual treatments or if an effective treatment seems to stop working, a thyroid problem, especially abnormally low thyroid functioning, might be to blame.
Several clinical studies have shown that hypothyroidism is surprisingly common in people with rapid-cycling bipolar disorder . One group of scientists tested for thyroid abnormalities in stored blood samples from almost four thousand patients hospitalized for psychiatric problems. They found a high association between thyroid abnormalities and a diagnosis of rapid-cycling bipolar disorder.
But it is also clear that some people with bipolar disorder whose thyroid hormone levels are in the normal range according to most laboratory standards can benefit from taking thyroid hormones . Studies have demonstrated that many people with bipolar depression symptoms who are not responding to treatment have thyroid function that is normal by the usual criteria, but a closer look reveals that their thyroid hormone levels are in what might be called the low normal or even barely normal range. It may be that people with depression need a higher level of thyroid hormones than those who are not depressed. Perhaps the extra thyroid hormone somehow makes these people more responsive to other treatments. People who have a partial response to lithium or other mood stabilizers may have better control of their mood symptoms if they take a small dose of thyroid replacement hormone, even if their thyroid hormone levels are normal .
As a paper on treating rapid-cycling bipolar disorder put it, normal thyroid [blood test results] should not discourage the clinician from pursuing thyroid supplementation in people with bipolar disorder. What dose of hormone to prescribe is determined by measuring hormone levels in the blood.
Another factor to consider is that a side effect of taking lithium can be a decrease in the amount of hormone the thyroid gland releases. This is because lithium has a blocking effect on the final step in hormone release into the bloodstream. This effect usually kicks in within weeks of starting lithium, but it can also sneak up on a person after years. For this reason, anyone for whom lithium is prescribed for bipolar disorder should have their thyroid hormone levels checked before they start on lithium, as well as a month or so later and then several times a year for as long as they take it.
I haven’t used the term thyroid medication in this discussion. That is because it has been possible for many years to synthetically produce the same molecules that the thyroid gland itself naturally produces. (Hence the brand name, Synthroid, which is the most commonly prescribed thyroid preparation.)
If, after years of mood stability, depression creeps back or moods start swinging again, don't despair—and get your thyroid checked.
For more on the use of thyroid hormones in the treatment of mood disorders, see: “Hormones and Nutritional Supplements” in: Francis Mark Mondimore, The Concise Guide to Bipolar Disorder, Baltimore, Johns Hopkins University Press, 2022.
Batter et al, " Rapid-cycling Affective Disorder I: Association with Grade 1 Hypothyroidism, " Archives of General Psychiatry 46:no.5 (1990) 427-32
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Francis Mondimore, M.D., is a psychiatrist with over 30 years of experience treating people with psychiatric disorders. He is an Associate Professor in the Department of Psychiatry and Behavioral Sciences at Johns Hopkins University School of Medicine.
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This article is part of the Bringwise Psychology Journal — daily insights on human behavior, mental health, and personal growth.