Why Testosterone Is Important

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Testosterone is an androgen hormone produced by the adrenal cortex, the testes, and the ovaries. It is often considered the primary sex hormone associated with those assigned male at birth. Testosterone stimulates the development of secondary sex characteristics associated with males (like body hair and muscle growth) and is essential in the production of sperm.

In those assigned female at birth, among other things, testosterone helps keep bones and the reproductive system healthy and contributes to the sex drive.

Man and woman in plank position, man with facial hair and bulkier muscles due to increased testosterone
Westend61 / Getty Images

Healthy assigned males who have gone through puberty have 15 times the levels of testosterone compared to a healthy person assigned female at birth.

Testosterone imbalances can cause infertility in any gender. Low levels of testosterone in cisgender men can cause infertility. High testosterone levels are associated with infertility in those who can get pregnant.

Testosterone levels can be evaluated with blood work. This is usually part of an infertility workup in all genders.

Hormonal Supplementation

Testosterone is a potent steroid hormone whose chemical formulation is C19-H28-O2. Testosterone is also known as 17-beta-hydroxy-4-androstene-3-one.

Prescription testosterone is used to treat hypogonadism-related conditions in cisgender men and delayed puberty in cis boys.

While off-label it might be used to treat perimenopause symptoms or a low sex drive, there are no Food and Drug Administration-approved (FDA) indications for testosterone prescription use in those assigned female at birth.

Another area of medicine where testosterone is prescribed is for transmasculine people (those assigned as female at birth but who exist as men).

It is available as a gel, topical solution, patch, or pellet (to be implanted), or as an injection or oral capsule.

Brand names include Androderm, AndroGel, AndroGel Pump, Aveed, Axiron, Depo-Testosterone, First-Testosterone, First-Testosterone MC, Fortesta, Natesto, Striant, Testim, Testopel, Vogelxo, and Vogelxo Pump.

Risks of Supplementation

Too much testosterone can cause infertility in any gender. Testosterone supplementation can also increase the risk of stroke, hypertension, accumulation of red blood cells, heart attack, leg clots, pulmonary embolus, and cancer. The FDA only approves its use for hypogonadism and does not recommend its use for low testosterone use due to aging. The Endocrine Society, on the other hand, supports its possible use in older men with confirmed testosterone deficiency aiming to achieve a low-normal level of the hormone, but only after carefully reviewing the risks and benefits.

Warning: Do not attempt to supplement testosterone on your own. There are a number of websites selling "testosterone supplements," and many are fake and even dangerous. Even if the testosterone supplement is real, it is not harmless and can worsen or cause infertility in any gender.


If you are having your testosterone levels checked, the blood test will likely be scheduled for the morning.

There are two kinds of testosterone found in your blood:

  • Free testosterone (also known as free T) is testosterone that is not chemically bound to anything else.
  • Bound testosterone makes up the majority of your total testosterone levels. Around 98 percent of the testosterone in your blood is bound to one of two proteins: albumin or sex hormone-binding globulin (SHBG).

When you have your testosterone levels tested, a doctor will look at both your free testosterone levels and your total testosterone levels.

Your total testosterone levels include both free and bound testosterone.

Total testosterone levels vary throughout the day. In cis men younger than 45, levels are highest in the morning and lower toward evening. Once over the age of 45, it doesn't matter what time of day levels are checked.

Normal ranges for testosterone partially depend on the lab and a doctor's interpretation. With that said, here are some general values.

For an assigned male age 19 or older:

  • Testosterone total should be between 270-1070-950 nanograms per deciliter (ng/dL).
  • Free testosterone should be between 50-210 pg/dL picograms per deciliter (pg/dL).

For an assigned female age 19 or older:

  • Testosterone total should be between 15-70 ng/dL.
  • Free testosterone should be between 1.0-8.5 pg/dL.

Testosterone Function

Development of sperm: Testosterone is essential to the production of sperm in the testes. It is a delicate balance, however. Both too little and too much testosterone can lead to low sperm counts.

Associated with what are known as secondary male characteristics: This includes facial and body hair growth, deepening of the voice, the building of muscle mass, increased size of bones, and distribution of fat in the body.

Infants have similar levels of testosterone. It is only during puberty that cisgender boys begin to produce significantly higher levels of testosterone, leading to the development of the secondary sex characteristics associated with males.

Those assigned female at birth with abnormally high levels of testosterone may have problems with facial hair, male pattern balding, and infertility. High testosterone levels are also associated with acne in any gender.

Essential to the development of eggs in the ovaries: Androgens play an important role in ovarian follicle development and estrogen production.

Sex drive (libido): The connection between testosterone and sex drive is well known. Higher levels of testosterone cause higher levels of sexual appetite.

Building muscle mass: Cisgender men are more likely to develop muscle mass than cis women because of their higher testosterone levels.

Pain tolerance: Testosterone may help people regulate pain levels.

Learning and memory, especially spatial intelligence: Testosterone aids in learning and memory. It is especially associated with spatial intelligence.

Cis men with abnormally low testosterone levels are at risk for learning disabilities.

Cognitive Empathy: Cognitive empathy involves being able to read another person’s emotions via their body language and facial expressions.

Higher testosterone levels are associated with a lessened ability to read people.

However, a new study out of the University of Toronto published in September 2019 found that giving men testosterone did not reduce their empathy.

Disease and Disorders That Affect Testosterone Levels

When testosterone levels are abnormally low or high, it affects the overall health and well-being of an individual. This is true for all genders. What can cause abnormal testosterone levels?

In cis men, possible causes of low testosterone include:

  • Age (after 50)
  • Being underweight or overweight
  • Smoking
  • Congenital or chromosomal disease like Klinefelter syndrome (XXY) or Kallmann syndrome
  • Problems with the pituitary gland
  • Diseases involving the testicles
  • Abnormally high levels of iron
  • Chemotherapy and other cancer treatments
  • Major illness or surgery
  • Some medications and recreational drugs
  • Extremely high levels of stress

In cis men, possible causes of abnormally high testosterone levels include:

  • Adrenal or testicular tumors
  • Anabolic steroid abuse
  • Testosterone supplementation
  • Having physical contact with someone using a topical testosterone supplement

In cis women, possible causes of high testosterone include:

In cis women, the most common cause of low testosterone is menopause.


Testosterone is an essential hormone for everyone. If your levels are abnormal, a doctor will likely order more testing to investigate the cause. For those whose levels are low due to the normal effects of aging, testosterone supplementation may be an option to consider.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. University of Rochester Medical Center. Total testosterone.

  2. MedlinePlus. Testosterone injection.

  3. MedlinePlus. Testosterone levels test.

  4. Long N, Nguyen L, Stevermer J. PURLS: It's time to reconsider early-morning testosterone tests. J Fam Pract. 64(7):418-9.

  5. Kaiser Permanente. Testosterone results.

  6. American Society for Reproductive Medicine. Testosterone use and male fertility.

  7. Harvard Health Publishing. Testosterone - what it does and doesn't do.

  8. Franks S, Hardy K. Androgen action in the ovaryFront Endocrinol (Lausanne). 9:452. doi:10.3389/fendo.2018.00452

  9. The Royal Society. https://royalsocietypublishing.org/doi/10.1098/rspb.2019.1062

Additional Reading

By Rachel Gurevich, RN
Rachel Gurevich is a fertility advocate, and recipient of The Hope Award for Achievement, from Resolve: The National Infertility Association. She is the author of "The Doula Advantage" and "Birth Plans for Dummies," and a member of the Association for Health Care Journalists. She has contributed to Reuters Health, USA Today, and more.