Obstructive sleep apnea (OSA) is common and has major health implications but treatment options are limited. OSA patients show a marked reduction in upper airway (UA) dilator muscle activity at sleep onset and this phenomenon leads to increased collapsibility of UA compared to normal subjects. In this protocol the investigators will test the effect of LTM1201AZ, LTM1201AT, LTM1201AD, LTM1201AG administered before sleep on OSA phenotype traits and OSA severity during sleep.

Inclusion Criteria:

• AHI > 10 events/h during NREM supine sleep

Exclusion Criteria:

• Any medical condition other than well controlled hypertension and mild diabetes.
• Any medication known to influence breathing, sleep/arousal, or muscle physiology.
• Claustrophobia.
• Inability to sleep supine.
• Allergy to any of the medications tested in the protocol.
• History of kidney stones, hypercalcemia, primary hyperparathyroidism, sarcoidosis, hypervitaminosis D.
• Individuals with underlying cardiac disease, such as arrhythmias.
• Individuals taking psychiatric medications, such as an MAO-I, SSRI or SNRI, or any of the studied medications for medical care.
• For women: Pregnancy.
• Pulmonary hypertension
• Severe OSA with a mean SaO2 lower than 88%