Testosterone is a powerful hormone in both men and women. It has the ability to control sex drive, regulate sperm production, promote muscle mass, and increase energy. It can even influence human behavior, such as aggression and competitiveness.

As you grow older, the level of testosterone in your body gradually decreases. This can lead to a variety of changes such as reduced sex drive. While lower testosterone levels may be concerning, it’s a natural part of aging.

The “normal” or healthy level of testosterone in the bloodstream varies widely, depending on thyroid function, protein status, and other factors.

For men ages 19 and up, normal testosterone levels range from 240 to 950 nanograms per deciliter (ng/dL). For women ages 19 and up, normal testosterone levels range from 8 to 60 ng/dL.

Testosterone levels reach their peak around age 18 or 19 before declining throughout the remainder of adulthood.

Testosterone is necessary for normal fetal development during pregnancy. It controls the development of the male reproductive system.

Testosterone levels in the womb may also affect how your right and left brain function, according to one study that looked at 60 children.

Testosterone levels have to fall within a very narrow margin in order for the fetal brain to be healthy. High levels of fetal testosterone may be linked to autism.

Testosterone levels are at their highest during adolescence and early adulthood.

In boys, the first physical signs of testosterone, or androgens, in the body are apparent during puberty. A boy’s voice changes, his shoulders broaden, and his facial structure becomes more masculine.

As men get older, their testosterone levels may decline about 1 percent per year after age 30.

In premenopausal women, testosterone is made mainly in the ovaries. Levels will decline after menopause, which usually begins between ages 45 and 55.

A testosterone test measures the level of the hormone in your blood.

Some people are born with conditions that cause low testosterone levels. You may have a low testosterone level if you have an illness that causes damage to your testicles or ovaries, which make the hormone.

Levels may drop as you grow older. However, the U.S. Food and Drug Administration (FDA) advises against getting testosterone replacement therapy (TRT) for low levels caused by aging alone.

Low testosterone levels can cause changes in sexual function, including:

Other signs of low testosterone levels include:

If you feel that you may have low testosterone levels, you should see your doctor and get a test.

Testosterone is the main male hormone, but women also need it for healthy body functioning. Testosterone is found in women at much lower levels than in men.

A woman’s estrogen level drops after she enters menopause. This may make her levels of male hormones, also known as androgens, somewhat higher. Diseases such as polycystic ovarian syndrome (PCOS) can also raise testosterone levels.

Excess testosterone in a woman’s bloodstream can cause:

Low testosterone in women can also cause fertility problems, in addition to weak bones and loss of libido.

The best way to diagnose low testosterone is to visit your doctor for a physical exam and a blood test.

Your doctor will look at your physical appearance and sexual development. Because testosterone levels are usually higher in the morning, the blood test should be performed before 10:00 a.m. in younger men. Men over 45 can be tested until 2:00 p.m. and still receive accurate results.

Risks associated with the blood test are rare but may include bleeding, pain at the injection site, or infection.

While symptoms of lowering testosterone may be a normal part of aging, they could also be signs of other underlying factors. These include:

Testosterone levels that are lower than the normal range could be caused by conditions such as:

Testosterone levels that are higher than the normal range may be caused by:

If your testosterone level is too low, your doctor may suggest TRT. Testosterone is available as:

Some medications used to treat high testosterone levels in women include:

It’s natural to be concerned about lower levels of testosterone. However, a gradual decrease is a normal part of aging. Talk to your doctor if you’re worried or experiencing abnormal symptoms.