Yes, testosterone is a hormone. Specifically, it’s a steroid hormone and the primary androgen (male sex hormone) in the human body. It belongs to a class of hormones built from cholesterol, which gives it the ability to pass directly into cells and influence gene activity from the inside. While testosterone is often associated with men, it plays important roles in women’s health too.
What Kind of Hormone Testosterone Is
Testosterone is classified as a C19 steroid hormone, meaning its molecular structure contains 19 carbon atoms arranged in the characteristic four-ring shape shared by all steroids. Your body manufactures it from cholesterol through a series of enzymatic steps. The process begins when a signaling hormone from the brain triggers cells to convert cholesterol into a precursor called pregnenolone, which is then modified step by step until it becomes testosterone.
Once in the bloodstream, testosterone works by entering cells and binding to androgen receptors inside the cytoplasm. This binding causes the receptor to change shape, release its companion proteins, and travel into the cell’s nucleus, where it attaches to DNA and switches specific genes on or off. Testosterone can also be converted into two other active forms: a more potent androgen called DHT (which binds to the same receptor about twice as strongly) and estradiol, a form of estrogen. These conversions allow a single hormone to have a wide range of effects in different tissues.
Where Your Body Makes It
In men, the vast majority of testosterone is produced in the Leydig cells of the testes. A smaller amount comes from the adrenal glands, which sit on top of the kidneys. In women, the ovaries and adrenal glands both contribute to testosterone production, though at much lower total amounts.
Production is tightly controlled by a feedback loop between the brain and the gonads. The hypothalamus releases a signaling molecule called GnRH, which tells the pituitary gland to secrete luteinizing hormone (LH). LH then travels to the testes and activates the Leydig cells to produce testosterone. When blood testosterone levels rise high enough, the hypothalamus detects this and dials back GnRH release, which in turn reduces LH and slows testosterone production. This cycle keeps levels within a relatively stable range throughout the day, though they naturally peak in the early morning.
What Testosterone Does in the Body
Testosterone’s roles begin before birth. During fetal development, it drives the formation of male internal and external reproductive organs, including testicular descent through the inguinal canal during the last two months of pregnancy.
At puberty, rising testosterone levels trigger a cascade of changes: growth spurts, deepening of the voice, growth of body and pubic hair, enlargement of the penis and testes, and increased sex drive. These are the secondary sexual characteristics most people associate with male development.
In adults, testosterone continues to serve several functions that go well beyond reproduction:
- Muscle and bone maintenance. Testosterone stimulates protein synthesis in skeletal muscle and helps maintain bone density. When levels drop, both muscle mass and bone strength tend to decline.
- Red blood cell production. It stimulates the process that creates new red blood cells, which is why men typically have higher red blood cell counts than women.
- Sex drive and fertility. Testosterone is essential for sperm production and is a key driver of libido in both men and women.
- Fat distribution and energy. Adequate levels help regulate where the body stores fat and contribute to overall energy and sense of well-being.
Normal Testosterone Levels
In men, testosterone is typically measured through a morning blood draw, since levels are highest early in the day. The general reference range for adult men is 300 to 1,000 ng/dL, though this varies slightly by laboratory. A large harmonized study across four cohorts in the U.S. and Europe found that the median level for healthy, nonobese men aged 19 to 39 was about 531 ng/dL, with the middle 90% falling between 303 and 852 ng/dL.
Levels decline gradually with age. The average drop is about 1% per year after age 30, which means a man in his 60s or 70s will typically have noticeably lower levels than he did in his 20s. The harmonized data reflect this: the median for men aged 40 to 49 was about 461 ng/dL, and for men 60 to 69 it was around 446 ng/dL. The decline is steepest in the lowest percentiles, meaning men who already had lower levels tend to see the most pronounced drop.
Women’s testosterone levels are substantially lower, generally in the range of 15 to 70 ng/dL, though standardized reference ranges for women are less well established.
What Happens When Levels Are Too Low
When testosterone falls below the normal range and symptoms are present, the condition is called hypogonadism. It’s generally diagnosed when morning testosterone is below 300 ng/dL on at least two separate blood tests, combined with characteristic symptoms.
The most telling signs include reduced sex drive, fewer spontaneous erections, shrinking testicular volume, and fatigue. Less specific but common symptoms include depressed mood, irritability, difficulty concentrating, increased body fat (especially around the midsection), decreased muscle mass, and reduced physical endurance. Loss of body hair and hot flashes can also occur. Because many of these symptoms overlap with other conditions, including depression and thyroid disorders, a blood test is necessary to confirm whether testosterone is actually the cause.
It’s worth noting that only men with both low lab values and associated symptoms are candidates for treatment. A number slightly below the reference range without any symptoms doesn’t automatically require intervention.
Testosterone in Women
Though produced in much smaller quantities, testosterone matters for women’s health. It contributes to libido, helps maintain bone density and muscle tissue, and plays a role in overall energy levels. Women’s testosterone levels also decline with age, particularly after menopause, which can contribute to reduced sex drive and changes in body composition. The biology is the same: testosterone binds to androgen receptors in women’s tissues just as it does in men’s, activating the same gene-regulating machinery at lower concentrations.