Clinical services Health Information Hormones in males What is testosterone? Testosterone is the most important androgen (male sex hormone) in men and it is needed for normal reproductive and sexual function, muscle and bone strength. Testosterone is important for the physical changes that happen during male puberty, such as development of the penis and testes, and for the features typical of adult men such as facial and body hair. Testosterone also acts on cells in the testes to make sperm. What controls the production of testosterone? The pituitary gland and the hypothalamus, located at the base of the brain, control the production of male hormones and sperm. Hormone messages are sent from these glands to the testes where testosterone is produced and sperm are made. The level of testosterone in the blood feeds back to the pituitary gland and the hypothalamus and when the level is low more hormone messages are sent to increase the production. The Luteinizing hormone (LH) and follicle stimulating hormone (FSH) are the two important messenger hormones made by the pituitary gland that act on the testes. LH is needed for the Leydig cells in the testes to make testosterone that leads to the production of sperm. Reproduction The testes hang ‘outside’ the body in the scrotum because sperm production needs a cooler temperature than the inside of the body. Because the testes are outside the main body cavity they are more vulnerable to injury, but also it is easier for a man to discover lumps or bumps. Testosterone deficiency In men with low testosterone levels, the symptoms that may be experienced include low energy levels, little interest in sex, feeling sad, down or depressed, mood, irritability, poor concentration, and reduced muscle strength. Symptoms often overlap with those of other illnesses. The symptoms of androgen deficiency are different depending on the age when testosterone levels are below the normal range. Use of testosterone replacement This hormone has been used for hormone deficiency treatment. Testosterone in Australia is only able to be prescribed by a specialist in the field. Off-label use to promote muscle development (when hormone levels are in the normal range) is not advised as this may lead to depression of natural hormone production, small testes and subsequent infertility.