Trazodone does not appear to have a meaningful effect on thyroid function. In clinical studies tracking thyroid hormones over long-term use, trazodone produced no clinically significant changes in thyroid function tests. However, the relationship between trazodone and thyroid health is worth understanding more fully, especially if you’re already managing a thyroid condition or noticing symptoms that could point to either medication side effects or a thyroid problem.
What Clinical Evidence Shows
A double-blind study published in the Journal of Clinical Psychopharmacology compared trazodone to imipramine (a tricyclic antidepressant) for long-term maintenance therapy in patients with moderate to marked depression. Researchers monitored a range of health markers throughout the study, including thyroid function, prolactin, growth hormone, blood pressure, and EKGs. The result: no clinically significant changes in any of these measures among patients taking trazodone. The study concluded that trazodone is safe for long-term use.
This is notable because some other psychiatric medications can influence thyroid hormone levels. Lithium, for example, is well known for causing hypothyroidism in a significant percentage of users. Trazodone does not share this risk based on available evidence.
Trazodone and Levothyroxine Together
If you take thyroid medication like levothyroxine, you may be wondering whether trazodone interferes with it. The interaction between these two drugs is classified as minor. Trazodone does not appear to block the absorption or reduce the effectiveness of thyroid hormone replacement.
Interestingly, the interaction works in the opposite direction. A small case series from 1990 found that adding thyroid hormone (specifically T3, the active form) seemed to enhance trazodone’s antidepressant effect. This is actually a strategy sometimes used with various antidepressants, where thyroid hormone acts as an “augmenter” to boost the medication’s mood benefits. The exact mechanism isn’t fully understood, but the key takeaway is that thyroid medication and trazodone don’t work against each other.
Symptoms That Overlap
One reason people search for this topic is that trazodone’s side effects can look a lot like thyroid problems. Both trazodone use and hypothyroidism (underactive thyroid) can cause constipation, fatigue, bloating, and weight changes. If you’re experiencing these symptoms after starting trazodone, it can be genuinely difficult to tell whether the medication is responsible or whether a thyroid issue is developing independently.
This overlap is a real source of confusion. In patient discussions on Mayo Clinic Connect, several people described persistent constipation and bloating while taking trazodone for sleep, and some of those same individuals also had hypothyroidism. Even after their thyroid levels normalized with medication, constipation persisted, suggesting trazodone was contributing to the symptom on its own. Other commonly reported trazodone side effects that mimic thyroid dysfunction include drowsiness, dry eyes, and nausea.
The practical way to sort this out is straightforward: a simple blood test measuring TSH (thyroid-stimulating hormone) can tell you whether your thyroid is functioning normally. If your TSH levels are in range and you’re still dealing with fatigue or constipation, trazodone’s side effects are the more likely explanation.
Why the Question Matters
Depression and thyroid disorders frequently coexist. Hypothyroidism itself can cause depression, low energy, and cognitive fog, which means some people taking trazodone for mood or sleep issues may have an undiagnosed or undertreated thyroid condition contributing to their symptoms. If trazodone isn’t helping as much as expected, a thyroid panel is a reasonable thing to ask about, not because trazodone caused the problem, but because both conditions can feed into the same symptoms.
For people already on thyroid replacement therapy, there’s no evidence that adding trazodone will disrupt your thyroid management. You don’t need to adjust your levothyroxine dose because of trazodone, and there’s no special timing requirement for separating the two medications (though levothyroxine is generally best taken on an empty stomach, as it always is). Your doctor may still want to check thyroid levels periodically, but that’s standard practice for anyone on thyroid medication regardless of what other prescriptions they take.