Androgens are male sex hormones that cause the development of secondary sex characteristics in males. The primary androgen is testosterone, which is produced in the testes and regulated by LH from the pituitary gland. Testosterone promotes the growth of male sex organs and secondary sex characteristics at puberty such as facial and body hair growth, deepening of the voice, and increased muscle and bone growth. It works by binding to androgen receptors and enhancing protein synthesis. Common androgen preparations are used to treat conditions like testicular failure, aging-related low testosterone, and erectile dysfunction. Phosphodiesterase type 5 inhibitors like sildenafil are a treatment for erectile dysfunction by enhancing the effects of nitric oxide