Abstract

Little is known about how psychotropic drugs influence thyroid function in man, but it has been reported that sertraline decreases the efficacy of levothyroxine in patients treated for hypothyroidism. Most psychotropic drugs are metabolized in the liver by cytochrome P450. Sertraline is metabolized by cytochrome P450 CYP 2D6, CYP 3A4, and CYP 2C19. Mianserin is metabolized by CYP 2D6, and to some extent also by CYP 3A4. Since both substances, at least in part, are metabolized by the same liver enzymes, drug interactions can be expected. In this article we describe such a possible interaction between sertraline and mianserin in a patient treated with levothyroxine for hypothyroidism (Hashimoto's thyroiditis). She displayed both clinical symptoms and laboratory data typical of hypothyroidism when long-term antidepressive sertraline therapy (100 mg/day) was transiently supplemented with mianserin (30 mg/day). All symptoms and signs of hypothyroidism disappeared completely when the mianserin treatment was discontinued. These findings imply that unexpected drug effects may occur in depressed patients with primary hypothyroidism if they are treated with both sertraline and mianserin. In such situations thyroid function should be checked carefully.