What Is Free Testosterone?

Testosterone is a hormone that plays a vital role in the male body. It is responsible for the development of male sexual characteristics, such as body hair and a deeper voice, as well as muscle growth and bone density. However, as men age, their testosterone levels tend to decrease, causing a range of low testosterone symptoms such as low libido, muscle loss, fatigue and erectile dysfunction. [1,2]

One of the key factors to consider when measuring testosterone levels is free testosterone vs total testosterone. [3] So, let's explain what free testosterone is and how it differs from total testosterone and what can be done to increase free testosterone levels.

What is Free Testosterone?

Testosterone is produced in the testes, ovaries and adrenal glands, [4] and it plays a crucial role in the body's development and maintenance. However, most testosterone in the body is bound to proteins such as sex hormone-binding globulin (SHBG) and albumin, [5] making it inactive. Free testosterone, on the other hand, is not bound to proteins and is therefore biologically active. It makes up only 2-3% of the total testosterone in the body, but it is the only form that can be used by the body's cells. [6]

How Free Testosterone Differs from Total Testosterone

Total testosterone is the sum of free testosterone and testosterone that is bound to proteins, [7] such as SHBG and albumin. While total testosterone levels are often used to diagnose hypogonadism (low testosterone), they do not provide an accurate picture of the body's testosterone levels. This is because some of the testosterone that is bound to proteins may not be biologically active, and therefore cannot be used by the body's cells. In contrast, free testosterone is the only form of testosterone that is biologically active and can be used by the body's cells.

The Importance of Free Testosterone

Free testosterone is important because it is the only form of testosterone that can interact with androgen receptors in the body's cells. [8] Androgen receptors are found in many tissues throughout the body, including the bones, muscles, brain and genitals. When free testosterone binds to these receptors, it triggers a range of physiological responses, including muscle growth, bone density, and the development of male secondary sexual characteristics. [9] Low levels of free testosterone can lead to a range of symptoms, including low libido, erectile dysfunction, fatigue and depression.

The Testosterone Life Cycle

Testosterone levels in men tend to peak during puberty and decline as men age. [10] As boys grow into their teenage years, testosterone levels surge, leading to the development of male secondary sexual characteristics and a strong libido. However, as men age, their testosterone levels tend to decline, leading to a range of symptoms such as low libido, erectile dysfunction and fatigue. While the reasons for this decline are not fully understood, it is thought to be related to a combination of genetic, environmental and lifestyle factors.

What Affects Free Testosterone Levels?

A range of factors can affect free testosterone levels, including age, genetics, lifestyle factors and medical conditions. As men age, their testosterone levels tend to decline, which can lead to a decrease in free testosterone levels. In addition, certain medical conditions, such as hypogonadism, can also lead to low testosterone levels. Other factors that can affect free testosterone levels include obesity, diabetes, high blood pressure, alcohol consumption and smoking. [11]

How to Test for Free Testosterone

Testing for free testosterone levels is a simple blood test that can be ordered by a healthcare provider or online privately. The test measures the amount of free testosterone in the blood, as well as the amount of total testosterone. While total testosterone levels are often used to diagnose hypogonadism, free testosterone levels provide a more accurate picture of the body's testosterone levels. In addition, testing for free testosterone levels can help diagnose conditions such as Klinefelter syndrome, which can cause low testosterone levels. You can find some examples of testosterone test kits here.

Increasing Free Testosterone Levels

There are several ways to increase free testosterone levels, including lifestyle changes, supplements and hormone replacement therapy. Lifestyle changes, such as regular exercise and a healthy diet, can help increase testosterone levels and reduce the risk of conditions such as obesity and diabetes, which can lead to low testosterone levels. 

Supplements such as DHEA and zinc have also been shown to increase testosterone levels, although the evidence is limited for many suppplements, certain deficiencies like zinc have been pretty thoroughly researched to impact test levels, and correcting these deficiencies has shown to work in a host of cases. [12]

Sleep is potentially the biggest lifestyle factor.

Hormone replacement therapy, such as testosterone replacement therapy (TRT), can also be used to increase testosterone levels in men with hypogonadism.

The Risks of Hormone Replacement Therapy

While hormone replacement therapy can be effective in increasing testosterone levels, it also carries a range of risks. TRT has been associated with an increased risk of cardiovascular disease, prostate cancer, and sleep apnea. [13]

In addition, whilst TRT is considered relatively safe, there is the fact that you may well be on it for the rest of your life and it could cause a range of side effects, including acne, hair loss, and mood swings. For this reason, it is important to discuss the risks and benefits of TRT with a healthcare provider before starting treatment.


1 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1476110/

2 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6119844/

3 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4255853/

4 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6761896/

5 - https://www.ncbi.nlm.nih.gov/gene/6462

6 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4975356/

7 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4255853/

8 - https://www.ncbi.nlm.nih.gov/books/NBK279000/

9 - https://www.ncbi.nlm.nih.gov/books/NBK526128/

10 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2544367/

11 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7824172/

12 - https://pubmed.ncbi.nlm.nih.gov/8875519/

13 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4212439/

14 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3897047/

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