Inclusion Criteria:

• * Adults
• * Obesity (BMI ≥ 30 kg/m2)

Exclusion Criteria:

• * Age \<19 or \> 50
• * BMI \< 30 kg/m2
• * Systolic blood pressure (SBP) \< 100, \> 150 mmHg
• * Current anti-hypertensive medication use, including diuretics
• * Current use of organic nitrates
• * Current use of PDE-5 inhibitors (sildenafil, tadalafil, vardenafil)
• * History of reaction to PDE-5 inhibitors
• * Known HIV infection
• * Use of medications that strongly alter CYP3A4 activity
• * History of myocardial infarction, angina, uncontrolled cardiac arrhythmia, stroke, transient ischemic attack, or seizure
• * Known non-arteritic ischemic optic retinopathy (NAIOR)
• * History of hearing loss
• * Estimated glomerular filtration rate (eGFR) \< 60 ml/min/1.73 m2 by the modified diet in renal disease (MDRD) equation
• * Hepatic transaminase (AST and ALT) levels greater than three times the upper limit of normal
• * Known pregnancy or breastfeeding or those unwilling to avoid pregnancy during the course of the study
• * History of priapism
• * Use in excess of four alcoholic drinks daily
• * History of diabetes mellitus or use of anti-diabetic medications
• * Known anemia (men, Hct \< 38% and women, Hct \<36%)
• * Menopause
• * Weight \> 300 pounds
• * Individuals with circadian rhythm disorders, shift workers, or those who travel across time zones frequently