In a 12 week double-blind, placebo-controlled randomized trial, 120 subjects with obesity (BMI≥30 kg/m2) and pre-diabetes (HbA1c, 5.7-6.4%) will be randomly assigned 1:1 to receive either placebo or 2 mg of controlled-release melatonin, taken orally every evening 1 hour before bed. The investigators will assess melatonin's effect on insulin sensitivity by performing a hyperinsulinemic euglycemic glucose clamp and β-islet cell function measured using a hyperglycemic clamp, as a primary endpoint. The investigator will also evaluating melatonin supplementation's effect on mean 24-hour ambulatory blood pressure, nocturnal blood pressure, and potential intermediates including endothelial function using brachial ultrasound, catecholamine production using 24-hour epinephrine and norepinephrine excretion, and renin-angiotensin system activation using measurements of plasma renin activity, angiotensin II, and urine aldosterone excretion. The final endpoint will be to evaluate melatonin supplementation's effect on cellular cytokine and CC family chemokine expression as well as high sensitivity C-reactive protein, IL-6, and TNF-α.