Can quetiapine (antipsychotic medication) cause hypothyroidism (low TSH levels)?

Quetiapine and Low TSH: Thyroid Effects

Yes, quetiapine can cause low TSH levels, which is associated with hyperthyroidism rather than hypothyroidism. According to the FDA drug label, quetiapine is known to cause thyroid hormone abnormalities, particularly decreases in T4 levels, but this can also affect TSH regulation 1.

Mechanism and Evidence

• Quetiapine has been documented to cause dose-related decreases in thyroid hormone levels, with approximately 20% reduction in total and free thyroxine (T4) at higher therapeutic doses, typically maximal within the first six weeks of treatment 1
• The FDA drug label specifically states that "the mechanism by which quetiapine affects the thyroid axis is unclear" 1
• In clinical trials, quetiapine treatment was associated with shifts in thyroid hormone levels, including decreases in T4 and T3, which can affect TSH regulation 1
• While the FDA label primarily mentions elevated TSH (hypothyroidism), systematic reviews have found evidence of both hypothyroidism and hyperthyroidism (low TSH) associated with quetiapine 2

Clinical Significance and Monitoring

• Thyroid abnormalities are documented consequences of quetiapine treatment and may have clinical implications as changes in thyroid hormones can affect a person's mental state 2
• The FDA recommends that "both TSH and free T4, in addition to clinical assessment, should be measured at baseline and at follow-up" in patients taking quetiapine 1
• In most cases, cessation of quetiapine treatment is associated with reversal of effects on thyroid hormones, regardless of treatment duration 1
• Patients with pre-existing thyroid conditions may be at higher risk for developing thyroid abnormalities while on quetiapine 3

Specific Thyroid Effects

• In short-term placebo-controlled trials, quetiapine was associated with decreases in total T4 (3.4% vs 0.6% for placebo), free T4 (0.7% vs 0.1%), total T3 (0.5% vs 0%), and free T3 (0.2% vs 0%) 1
• While the FDA label primarily reports TSH increases (3.2% vs 2.7% for placebo), case reports and systematic reviews have documented instances of both elevated and decreased TSH levels 1, 2
• A 2020 case report specifically documented quetiapine-induced central hypothyroidism (with low TSH), suggesting that quetiapine may affect the hypothalamic-pituitary axis rather than just the thyroid gland directly 4

Management Recommendations

• For patients on quetiapine who develop thyroid abnormalities, monitoring both TSH and free T4 is essential as TSH alone may not accurately reflect thyroid status 1
• Patients with compromised thyroid function who receive treatment with quetiapine should have increased awareness of possible thyroid dysfunction and consideration of regular thyroid function monitoring 3
• In cases where thyroid abnormalities develop, clinicians should consider the temporal relationship to quetiapine initiation or dose changes 2
• For patients with pre-existing thyroid conditions, closer monitoring may be warranted when starting or adjusting quetiapine dosage 3

Important Caveats

• The relationship between quetiapine and thyroid dysfunction is not always clear-cut, as many patients with mental illness may have underlying thyroid abnormalities independent of medication effects 5
• Other medications commonly prescribed alongside quetiapine may also affect thyroid function, complicating the clinical picture 6
• Thyroid abnormalities may be transient and resolve without discontinuation of quetiapine in some cases 1
• Distinguishing between primary (thyroid gland) and central (hypothalamic-pituitary) mechanisms of thyroid dysfunction is important for proper management 4