Mirtazapine is an α_2A antagonist and mixed 5-HT₂/5-HT₃ antagonist that has been proposed as a potential treatment for obstructive sleep apnea (OSA). A small, randomized, controlled trial has previously found an approximate halving in the severity of OSA with daily doses of 4.5 and 15 mg. We aimed to confirm and extend these findings in 2 randomized placebo-controlled, proof-of-concept trials.

Two randomized, double-blind, placebo-controlled trials of mirtazapine for OSA (apnea-hypopnea index 10–40/h). Study 1: 3-way crossover, dose-finding study testing the self-administration of mirtazapine (7.5, 15, 30, and/or 45 mg) or placebo 30 minutes prior to bedtime for 2 weeks at each dose. Twenty patients were randomly assigned to 1 of 6 different dose-sequence groups, with each patient exposed to a maximum of 3 doses. Study 2: 3-arm, randomized, parallel-group trial of mirtazapine at 15 mg or mirtazapine 15mg + Compound CD0012 or placebo for 4 weeks in 65 patients with OSA.

Two patients withdrew from Study 1 after complaints of unacceptable lethargy. Fifteen patients were withdrawn from study 2, 7 after complaints of unacceptable lethargy or other side-effects. No measurement of sleep apnea improved due to mirtazapine in either study. Weight gain was significantly greater on mirtazapine than on placebo in both trials.

Mirtazapine did not improve sleep apnea in either trial. Mirtazapine caused weight gain, which may further worsen OSA. Therefore, mirtazapine is not recommended for the treatment of OSA.