Testosterone, Metformin, or Both, for Hypogonadism in Obese Males

Inclusion Criteria: * Men aged 18 to 50 years. * BMI \> or = 30 kg/m2. * Total testosterone levels \<2.3 ng/ml (\<8 nmol/l) or testosterone levels 2.3-3.49 ng/ml (8-12 nmol/l) and free testosterone levels \<70 pg/ml. * LH levels \<7.7 mIU / ml. * No evidence of any other pituitary hormone disruption in morning blood sample (normal concentrations of TSH, FT4, Prolactin, ACTH, cortisol and IGF-1 * Being able to provide informed consent before randomization and agree to comply with all the procedures included in the protocol. Exclusion Criteria: * Intolerance/allergy to metformin or testosterone undecanoate. * Previous diagnosis of diabetes mellitus (HbA1c\> 6.5% or fasting glucose\> 126 mg/dl or glucose\> 200 mg/dl after an oral glucose tolerance test) * Treatment with oral hypoglycemic agents, insulin or GLP-1 analogs. * Poor kidney function: serum creatinine\> 2.0 mg / dl. * Previous history of prostate cancer or breast cancer. * Active cancer of any kind. * History of liver tumor or acute or chronic liver disease with impaired liver function: total bilirubin\> 2.0 mg / dl or GOT levels three times the upper limit of normal. * Central hypogonadism of organic cause * Use in the past 12 months of any drug that affects the pituitary-gonadal axis. * Use of oral testosterone, oral or transdermal within 2 weeks prior to study entry, or any testosterone ester in the last 6 weeks or testosterone undecanoate injection in the 6 months prior to study entry. * Uncontrolled hypertension (SBP\> 160 mmHg or DBP\> 100 mmHg) despite adequate antihypertensive therapy. * HIV infection or known active infection with HBV or HCV. * Thrombotic or embolic disease. * Heart disease, kidney or liver disease. * Epilepsy or migraine not adequately controlled with treatment. * Hematocrit\> 50% in the screening. * PSA\> 4 ng / ml. * Severe benign prostatic hypertrophy with an IPSS scale score over 19. * Evidence of drug or alcohol abuse (\> 50 g alcohol / day) * Hematological diseases that produce increased risk of bleeding after intramuscular injection. * Serious underlying disease that might affect the patient's ability to participate in the study (eg ongoing infection, gastric ulcers, active autoimmune disease). * Reduced life expectancy (\<12 months) by the presence of comorbidities or advanced terminals. * Participation in another clinical trial within 30 days before study entry. * Previous diagnosis of hemochromatosis * Treatment with phosphodiesterase-5 inhibitors: sildenafil, tadalafil or vardenafil