Free thyroxine and thyroid-stimulating hormone in severe mental disorders: A naturalistic study with focus on antipsychotic medication.

Background: Disturbances in thyroid function have been associated with use of psychotropic drugs, including antipsychotics. Still, the thyroid function in relation to commonly prescribed antipsychotic drugs and polypharmacy is not fully known. We investigated thyroid function associated with use of antipsychotics in patients with psychotic disorders compared with healthy controls.
Methods: We included 1345 patients and 989 healthy controls from the Thematically Organized Psychosis (TOP) study, recruiting participants between 18 and 65 years of age in the Oslo-area. All patients underwent a thorough clinical investigation and assessment of medication data. Thyroid function was determined from plasma levels of free thyroxin (fT4) and thyroid-stimulating hormone (TSH). Multiple linear regression analyses were performed to evaluate the association between thyroid parameters and use of antipsychotics, and monotherapy users of olanzapine, quetiapine, aripiprazole or risperidone (N = 473) were investigated separately.
Results: We found lower levels of fT4 (median 13.70 vs 14.00, p < 0.001) in patients compared to healthy controls, and a prevalence of 12.9% of previously undiagnosed deviant thyroid states in the patient group. Lower fT4 levels was associated with use of antipsychotics in general (p = 0.001), and quetiapine (p = 0.003) and olanzapine (p = 0.018) in particular, while the associations with TSH were non-significant. Using antipsychotics in combination with other psychotropic drugs, and with antidepressants in particular, was associated with lower fT4 level (p < 0.001) than use of antipsychotics alone.
Conclusions: Our findings indicate an association between use of antipsychotics and lower fT4. Clinicians should be aware that patients using quetiapine, olanzapine or antipsychotics in psychotropic polypharmacy are especially at risk.
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