Identifying Sleep Apnea Patients That Best Respond to Atomoxetine Plus Oxybutynin Therapy

Inclusion Criteria: * Suspected or diagnosed OSA * Recent drug induced sleep endoscopy results available (performed as part of routine clinical care). Exclusion Criteria: * Any uncontrolled medical condition * Current use of the medications under investigation * Use of medications expected to stimulate or depress respiration (including opioids, barbiturates, doxapram, almitrine, theophylline, 4-hydroxybutanoic acid). * Current use of hypnotic medications (trazodone, eszopiclone, benzodiazepines). * Current use of SNRIs/SSRIs or anticholinergic medications. * Conditions likely to affect obstructive sleep apnea physiology: neuromuscular disease or other major neurological disorder, heart failure (also below), or any other unstable major medical condition. * Respiratory disorders other than sleep disordered breathing: chronic hypoventilation/hypoxemia (awake SaO2 \< 92% by oximetry) due to chronic obstructive pulmonary disease or other respiratory conditions. * Other sleep disorders: periodic limb movements, narcolepsy, or parasomnias. * Contraindications for atomoxetine and oxybutynin, including: * hypersensitivity to atomoxetine or oxybutynin (angioedema or urticaria) * pheochromocytoma * use of monoamine oxidase inhibitors * benign prostatic hypertrophy, urinary retention * untreated narrow angle glaucoma * bipolar disorder, mania, psychosis * history of major depressive disorder (age\<24). * history of attempted suicide or suicidal ideation within one year prior to screening * clinically significant constipation, gastric retention * pre-existing seizure disorders * clinically-significant kidney disorders (eGFR\<60 ml/min/1.73m2) * clinically-significant liver disorders * clinically-significant cardiovascular conditions * moderate-to-severe hypertension (SBP\>180 mmHg or DBP\>110 mmHg measured at baseline; average of evening and morning measures\*) * cardiomyopathy (LVEF\<50%) or heart failure * advanced atherosclerosis * history of cerebrovascular events * history of cardiac arrhythmias e.g., atrial fibrillation, QT prolongation * other serious cardiac conditions that would raise the consequences of an increase in blood pressure or heart rate * myasthenia gravis * Claustrophobia * Pregnancy or nursing n.b. Development of new hypertension that is recognized on the final day of study medications during outcomes collection will not be used as stopping criteria for discontinuing outcomes collection. Participants that are sexually active and able to become pregnant must agree to use birth control for the entire study.