The study is designed to examine the efficacy and safety of AD109 to treat obstructive sleep apnea. The study is a four-period single-dose randomized crossover design in which patients will undergo overnight polysomnographic (PSG) testing with dosing of one of the following 4 treatments: AD109, atomoxetine, R-oxybutynin or placebo. Participants will return 2 weeks after their final crossover PSG for an end of study (EOS) visit.