A Trial of Tadalafil and Glycemic Traits

• Insulin Sensitivity, as measured by the Matsuda index [ Time Frame: 3 months ] [ Designated as safety issue: No ]
  Change in insulin sensitivity (as measured by the Matsuda index).
• Endothelial function [ Time Frame: 3 months ] [ Designated as safety issue: No ]
  reactive hyperemia index, using EndoPAT device

The purpose of this study is to find out if tadalafil can help overweight and obese people metabolize blood sugar more efficiently. The investigators also want to find out if 20 mg/day of tadalafil for 3 months is safe to take without causing too many side effects. The investigators are plan to enroll 100 subjects at Massachusetts General Hospital (MGH).

This study is examining changes in insulin resistance and glucose tolerance following 3 months of treatment with oral, once daily tadalafil.

The investigators primary hypotheses are that measurable decreases in insulin resistance (as measured by HOMA-IR) and increases in insulin sensitivity (as measured by the Matsuda index) will occur following 3 months of treatment with oral tadalafil 20 mg daily compared to placebo.

The investigators secondary hypotheses are that improvements in average glycemia (as measured by hemoglobin A1C), pancreatic beta cell function (as measured by the oral disposition index), and body composition (including weight, waist circumference, body mass index, and waist-hip ratio) will occur as a result of tadalafil-mediated changes in the cGMP pathway.

• Cardiovascular Disease
• Insulin Resistance
• Glucose Intolerance
• Obesity

• Drug: Tadalafil
  20 mg Tadalafil taken once a day for 3 months
  Other Name: Adcirca, Cialis
• Drug: Placebo
  Placebo tablet taken by mouth once a day for 3 months
  Other Name: Sugar pill

• Active Comparator: Tadalafil
  20 mg Tadalafil tablet taken by mouth once a day for 3 months
  Intervention: Drug: Tadalafil
• Placebo Comparator: Placebo
  Placebo tablet taken by mouth once a day for 3 months
  Intervention: Drug: Placebo

Inclusion Criteria:

• Age > 18 years and < 50 years
• BMI > 30 kg/m2

Exclusion Criteria:

• 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 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%)