Levothyroxine in psychiatry: issues related to absorption after oral dosing.

J Clin Psychiatry 2013;74(8):e744–e746 (doi:10.4088/JCP.13f08668) © Copyright 2013 Physicians Postgraduate Press, Inc. T prevalence of hypothyroidism is about 0.3%; the disorder is more common with increasing age and in women relative to men.1 Subclinical hypothyroidism occurs in 4%–20% of adults, depending on the population studied and the disease definition applied.2 Clinical and subclinical hypothyroidism are sometimes observed in psychiatric disorders. For example, these endocrine states may be associated with developmental delay or mental retardation,3 mood or cognitive disturbance in the elderly,4 dementia,5 psychosis,6 depression,7 bipolar disorder,8 rapid-cycling mood disorder,9 and other conditions. Hypothyroidism may also be an adverse outcome of lithium therapy.10 Levothyroxine (T4) supplementation is commonly considered in such situations and when depressed patients are medication refractory.11 Once patients have been stabilized on T4 therapy, the dose tends to remain constant for years.12 However, problems could arise from situations that affect T4 absorption, and psychiatrists may not be familiar with these pharmacokinetic matters. This article therefore examines clinically significant food and drug interactions, with specific focus on T4 absorption after oral dosing.