The chemical structure of testosterone.
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Testosterone is a male sex hormone that is important for sexual and reproductive development. Women also produce testosterone, but at lower levels than men.
Testosterone is part of a class of male hormones called androgens. In men, testosterone is produced mainly in the testes, and production is controlled by the brain's hypothalamus, and also the pituitary gland.
Testosterone is involved in the development of male sex organs, and the development of secondary sex characteristics at puberty, such as voice deepening and growth of facial and body hair.
The hormone also plays a role in sperm production, fat distribution, maintenance of muscle strength and mass, and sex drive, according to the Mayo Clinic.
In women, testosterone is produced in the ovaries and adrenal glands. Women’s total testosterone levels are about a tenth to a twentieth of men’s levels.
Levels of testosterone naturally decrease with age, but exactly what level constitutes "low T" or hypogonadism, is controversial. Testosterone levels vary wildly, and can even differ depending on the time of day they're measured (levels tend to be lower in the evenings.) Doctors typically to treat men for hypogonadism if they have symptoms of low testosterone — such as reduce sex drive and energy — and their testosterone levels are below 300 nanograms per deciliter.
High testosterone levels in women can lead to irregular menstrual cycles, increases in body hair and acne, and a deepening of the voice. Women with polycystic ovarian syndrome have high levels of male hormones, including testosterone, which can be a cause of infertility.
In older men with true testosterone deficiencies, testosterone treatment has been shown to increase strength and sex drive, experts say.
But sometimes,symptoms such as decreased energy and low sex drive are due to conditions such as depression. Treating these men with testosterone hormone won't improve symptoms.
One side effect of testosterone treatment is that it lowers sperm count, so experts recommend that men who desire future fertility avoid testosterone treatments.