1. Ada
  2. Testosterone


  1. What is testosterone?
  2. What does testosterone do?
  3. How is testosterone controlled?
  4. Low levels
  5. High levels
  6. Testosterone replacement therapy
  7. FAQs

What is testosterone?

Testosterone is a predominantly male sex hormone, belonging to a group of androgens (steroids) that are central to sexual and reproductive development. Females also produce testosterone, although in smaller quantities.

In males, testosterone is produced primarily in the testes, by the Leydig cells. In females, testosterone is mainly produced in the ovaries, which also produce estrogen. In both sexes, a small amount of testosterone is also produced in the adrenal glands.

Testosterone levels can fluctuate greatly, even over the course of a single day. The overall level of testosterone in the body tends to decrease as a result of aging. A deficiency of the hormone can also occur prenatally and during puberty. Some people may experience unusually high levels of testosterone. This is most common in children and young adults and also occurs in some females, as a result of a variety of underlying medical conditions.

Testosterone therapy, a treatment method involving an artificial form of the hormone, may be necessary for those experiencing low levels of testosterone. There are, however, possible side-effects, such as a lowered sperm count (in males) and acne, as well as cardiovascular problems.[1]

What does testosterone do?

Given its role in several bodily processes, testosterone is considered highly important to the overall health of males and females.

During the gestation of a fetus, testosterone is critical to the development of the internal and external male sex organs. The hormone also plays an important role during puberty, helping to enact many of the bodily changes that take place as the body matures.

Changes that occur during puberty include:

  • Growing taller
  • Developing pubic and body hair
  • In males, the enlargement of the penis and testes
  • Behavioral changes

During and after puberty – in males and females – testosterone also helps to enhance the libido and, in males, to produce sperm.[2]

By encouraging the production of red blood cells, testosterone also helps to maintain healthy bones and muscle.

How is testosterone controlled?

The human male and female reproductive cycles are controlled by the interaction of hormones from the brain’s hypothalamus and anterior pituitary[3] with hormones from reproductive tissues and organs. In both sexes, the hypothalamus monitors and causes the release of hormones from the pituitary gland.

Low levels of testosterone

Low testosterone, or a testosterone deficiency, can occur prenatally, during puberty and develop in adult males and sometimes females, too.

If the deficiency occurs prenatally (during pregnancy), the sexual development and process of masculinization may be affected as a male child matures. A male child with low levels of testosterone may experience delayed puberty, which will typically involve slow or no growth and a failure to develop the characteristics associated with puberty, including penis and testes enlargement, voice deepening and pubic and body hair growth. Those with a testosterone deficiency may also struggle to develop normal muscle mass and have lesser endurance capabilities.[2]

A testosterone deficiency can also develop as a result of aging, as well as being associated with conditions including obesity, type 2 diabetes and high blood pressure. The symptoms of a testosterone deficiency may be physical and psychological in nature.[4]

Symptoms in males

Testosterone deficiency in males may include the following symptoms:


  • Change in sleep patterns - insomnia or sleep disturbances
  • Increased body fat and reduced muscle mass
  • Reduced sexual desire, sexual dysfunction or infertility


A decreased libido and general fatigue are the most common symptoms of a testosterone deficiency. However, some males with low levels of testosterone may experience no symptoms at all, or only some of the symptoms listed above. If you are concerned that you may have a health condition, you can try using the Ada app for a free assessment.

Symptoms in females

Females can also experience testosterone deficiency. Symptoms of testosterone deficiency in females may include:


  • Loss of muscle mass and strength
  • Loss of libido


  • Lethargy
  • Lack of motivation
  • Low levels of wellbeing
  • Low mood

High levels of testosterone

The effect of high levels of testosterone in males and females largely depends on age. In children with high testosterone levels, it may lead to different presentation of the secondary sexual characteristics, typically more evident ones, and may include premature signs of puberty and growth spurts. This may result in a condition known as precocious puberty, wherein puberty occurs at an unusually early age, generally considered to be before the age of eight in girls and nine in boys. Precocious puberty can lead to less positive outcomes in physical development, as well as psychological changes, such as increased anger, which have been linked to higher testosterone production. However, this can generally be managed with treatment.[5]

Unusually high levels of testosterone in a female may be diagnosed as hyperandrogenism, a condition involving an excess of androgens (male sex hormones, including testosterone) in the body. Symptoms of hyperandrogenism can include acne, hirsutism (excessive body hair), virilization (typical masculine traits) and reproductive problems when presenting in females of reproductive age.[6][7] In most cases, the condition develops as a result of an underlying medical condition, including various diseases of the ovaries, adrenal gland and pituitary gland. Treatment will generally involve treating the underlying cause of the condition and possible hormone therapy.[8] If you are concerned about any symptoms, you can try using the Ada app for a free assessment.

Testosterone replacement therapy

In people with unusually low levels of testosterone, testosterone replacement therapy (TRT) may be recommended by a doctor. While more commonly prescribed for males, TRT is sometimes prescribed for females, too.[9]

Testosterone replacement therapy comes in a variety of forms, including:[10]

  • Skin patches (transdermal patches): A patch worn on the arms or upper body.
  • Mouth patch: A patch applied twice a day, that sticks to the gum above the incisor tooth.
  • Gels: Applied directly to the skin.
  • Injections: Injected directly into the muscle and absorbed into the bloodstream.

TRT should not be undertaken by anyone with normal testosterone levels to enhance sexual performance, for the purposes of bodybuilding or to prevent the natural results of aging. Before recommending TRT, a doctor will typically perform a full physical examination and carry out blood tests to accurately diagnose a testosterone deficiency.[11]

Side-effects of testosterone replacement therapy

Before advising TRT, a doctor will explain the possible side-effects of the treatment method. These may include:[11]

  • Reduced sperm count and possible infertility
  • Reduction in testicle size
  • Acne
  • Breast swelling or soreness in females
  • High red blood cell count
  • Swelling of the ankles or feet

Testosterone supplements can have serious side-effects, and the long-term risks are not yet fully known. There seems to be a direct correlation with an increase in cardiovascular problems. Testosterone supplements should only be prescribed by a doctor, after confirming that a person’s testosterone levels are low enough to need treatment.[12]

Testosterone FAQs

Q: What are normal levels of testosterone?
A: Testosterone levels vary according to the age and sex of a person. For adult males, the range considered to be normal in blood tests, is approximately 270 to 1100 nanograms per deciliter. For adult females, it is considered to be approximately 6-86 nanograms per deciliter.[13] However, the ranges used tend to differ by laboratory. If a person’s testosterone levels appear to be low, testosterone replacement therapy will typically only be recommended where symptoms are also present.[14][15][16][17]

Q: Is it possible to increase one’s testosterone levels naturally?
A: A number of over-the-counter supplements claim to use natural ingredients to increase a person’s testosterone levels. However, the effects and safety of these supplements has not been widely studied. It is not advisable to take any kind of testosterone supplement that has not been prescribed by a doctor who has deemed treatment necessary.[18]

It may be possible to help promote healthy levels of testosterone by making lifestyle changes that include:[19]

  • Getting regular exercise
  • Eating a balanced diet
  • Getting enough sleep
  • Reducing stress levels

  1. Live Science. “What is Testosterone?” June 22, 2017. Accessed September 14, 2017.

  2. You and Your Hormones. “Testosterone.” January, 2015. Accessed September 14, 2017.

  3. The hypothalamus and anterior pituitary are small glands that are part of the brain.

  4. The American Journal of Medicine. “Testosterone Deficiency.” July, 2011. Accessed September 15, 2017.

  5. Patient. “Precocious Puberty.” September 7, 2015. Accessed August 15, 2017.

  6. NCBI. “Diagnosis of hyperandrogenism: clinical criteria.” June, 2006. Accessed September 15, 2017.

  7. Medscape. “Androgen Excess.” March 14, 2018. Accessed April 7, 2018.

  8. DermNet New Zealand. “Hyperandrogenism.” February, 2014. Accessed September 15, 2017.

  9. Mayo Clinic. “Testosterone therapy in women: Does it boost sex drive?” April 21, 2016. Accessed April 17, 2018.

  10. WebMD. “Testosterone Replacement Therapy.” October 20, 2016. Accessed September 15, 2017.

  11. Urology Care Foundation. “Update For Men on Testosterone Replacement Therapy (TRT).” April, 2012. Accessed September 15, 2017.

  12. World Journal of Men’s Health. “Testosterone Replacement Therapy and Cardiovascular Risk: A Review.” December, 2015. Accessed April 7, 2018.

  13. Mayo Clinic. “Test ID: TGRP - Testosterone, Total and Free, Serum.” Accessed April 18, 2018.

  14. Healthline. “Testosterone Levels by Age.” March 23, 2015. Accessed April 14, 2018.

  15. Norfolk and Norwich University Hospitals. “Joint Trust Guideline for the Adult Testosterone Replacement and Monitoring.” January 10, 2017. Accessed April 14, 2018.

  16. The Journal of Sexual Medicine. “Testosterone reference ranges in normally cycling healthy premenopausal women.” October, 2011. Accessed April 14, 2018.

  17. American Association for Clinical Chemistry. “Testosterone Reference Ranges Vary Widely in U.S. Laboratories.” June 16, 2016. Accessed April 14, 2018.

  18. Cleveland Clinic. “Beware of ‘Natural’ Testosterone Boosters for ‘Low-T’.” November 14, 2013. Accessed April 14, 2018.

  19. Medscape. “Low Testosterone Levels Can Improve With Weight Loss, Exercise.” June 26, 2012. Accessed April 17, 2018.