Testosterone is a steroid hormone produced in the adrenal glands of both sexes and in the testes of males and the ovaries of females. Testosterone is largely responsible for the formation and maintenance of male sex characteristics, including both the larger bone and muscle development seen in males. The testosterone levels in humans are regulated by hormones released from the brain; in males the hypothalamus and pituitary glands in the brain increase testosterone during puberty and male characteristics develop (for example, penile enlargement, facial hair, interest in sex).
If a young man's low testosterone is a problem for a couple trying to get pregnant , gonadotropin injections may be an option in some cases. These are hormones that signal the body to produce more testosterone. This may increase the sperm count. Hedges also describes implantable testosterone pellets, a relatively new form of treatment in which several pellets are placed under the skin of the buttocks, where they release testosterone over the course of about three to four months. Injections and nasal gels may be other options for some men.