Opioid Antagonism in Hypogonadotropic Hypogonadism

Inclusion * Male * Age 18-75 years * Confirmed diagnosis of hypogonadotropic hypogonadism (low testosterone) * All medical conditions stable * Normal blood pressure (systolic BP \< 140 mm Hg, diastolic \< 90 mm Hg) * Negative urine drug screening panel * Hemoglobin * Men on adequate testosterone replacement therapy: normal male reference range * Men off testosterone replacement therapy: no lower than 0.5 gm/dL below the lower limit of the reference range for normal women Exclusion * Any condition (medical, mental, or behavioral) that, in the opinion of a study investigator, would likely interfere with participation in/completion of the protocol * Current or recent use of a medication (including hormonal replacement) that, in the opinion of a study investigator, can modulate the reproductive axis and, if applicable, unwilling to complete an appropriate washout for that particular medication and its method of administration * Current or recent use of a medication that affects the opioid pathway * Active illicit drug use