FSH
FSH, or follicle-stimulating hormone, helps control the production of sperm. FSH levels in men do not change very much, though they are usually low until puberty, when levels begin to rise.
LH
LH, or luteinizing hormone, causes the testicles to make testosterone, a hormone the body needs to produce sperm. LH levels in men do not change very much, though they are usually low in early childhood and begin to rise a couple years before the start of puberty.
Prolactin
Prolactin is a hormone secreted by the pituitary glands. In men, high levels of prolactin could cause decreased testosterone levels and lead to decreased energy and low sex drive in the short term, and decreased muscle mass and body hair in the long term. High prolactin levels can also cause erectile dysfunction, infertility, and, less commonly, secretion of milk from male breasts.
Testosterone
In people assigned male at birth (AMAB), testosterone is primarily produced by the testes, with a small amount produced by the adrenal glands. Free testosterone is not attached to proteins, whereas total testosterone includes free testosterone and testosterone that is bound to the proteins (e.g. albumin and sex hormone binding globulin) in the blood. While commonly regarded as the primary male sex hormone, testosterone is important for bone density, libido, body fat distribution, and supporting muscle mass across all sexes.
