Testosterone Therapy: What It Does, When It Helps, and How to Know if You Would Benefit From it

Introduction

Testosterone is often thought of as simply a “male hormone,” but it plays critical roles in both men and women. This article explains what testosterone does in the body, the symptoms of deficiency, evidence for its benefits, how to interpret laboratory testing—including the difference between “normal” and “optimal” hormone levels…

What Does Testosterone Do?

Testosterone is a steroid hormone produced mainly by the testes in men and the ovaries and adrenal glands in women.¹ It has both anabolic (tissue-building) and androgenic (masculinizing) effects. Its actions extend far beyond sexual function:

• Muscle and bone: Stimulates protein synthesis, increases lean body mass, improves muscle strength, and supports bone formation and mineralization.²⁻³
  
  
• Sexual function: Regulates libido in both sexes; supports erectile function in men and contributes to sexual desire and arousal in women.⁴
  
  
• Cognition and mood: Influences energy, mood stability, cognitive performance, and overall well-being.⁵⁻⁶
  
  
• Metabolic regulation: Affects insulin sensitivity, reduces visceral fat distribution, and lipid metabolism.⁷ Testosterone raises the basal metabolic rate by increasing lean body mass. It enhances mitochondrial function and energy production. It also enhances T4 to T3 conversion which improves thyroid function.
  
  
• Cardiovascular function: Modulates vascular tone and endothelial health.⁸ It does this by stimulating nitric oxide production. It restores the ability of the coronary arteries to dilate which can improve symptoms such as angina and exercise intolerance. It also reduces total cholesterol and LDL cholesterol levels as well as triglycerides.
  
  

Symptoms of Testosterone Deficiency

Men

Typical symptoms include reduced libido, erectile dysfunction, decreased muscle mass and strength, increased fat mass, fatigue, depressed mood, anemia, cognitive slowing, and reduced bone density.⁹⁻¹¹ These may develop gradually and overlap with other hormonal or metabolic issues.

Women

Testosterone deficiency in women is less often recognized but can present with reduced libido, fatigue, low energy, poor sleep, sweating at night, mood changes, weight gain, reduced bone density, and cognitive complaints such as “brain fog.”¹²⁻¹³ 

Benefits of Testosterone Therapy

Testosterone therapy does so much more than improve sex drive. Not only will it improve symptoms such as fatigue, insomnia, brain fog, and night sweats, there is strong evidence that testosterone therapy has the following benefits:

• Bone Health

Testosterone therapy increases bone mineral density and bone strength in men with testosterone deficiency.³ ¹⁴ In women, testosterone has been associated with preservation of bone density and improvements in lean mass.¹²

• Breast Cancer Risk in Women

Long-term observational data in more than 2,000 women receiving subcutaneous testosterone therapy showed a lower incidence of invasive breast cancer compared with age-matched SEER data.¹⁵ Additional research in women who took testosterone to transition to man suggests testosterone may reduce epithelial breast tissue volume, potentially conferring a protective effect.¹⁶⁻¹⁷

• Cognitive Function and Dementia

Several studies link low testosterone to cognitive decline and Alzheimer disease.⁵ Small clinical trials show improvements in spatial and verbal memory and executive function in hypogonadal men receiving therapy.⁶ Emerging data in women show improvements in energy and cognition with physiologic testosterone replacement.¹² ¹³

• Cardiovascular and Metabolic Effects

Earlier concerns about cardiovascular risk have been tempered by newer evidence. Testosterone therapy in appropriately selected men appears to improve lipid profiles, insulin sensitivity, fat distribution, and vascular function, without increasing adverse cardiovascular events when monitored properly.⁷⁻⁸ ¹⁸ Observational studies suggest reduced all-cause mortality in men whose testosterone is normalized with therapy.¹⁹

• Quality of Life and Sexual Function

Randomized and observational studies confirm that testosterone therapy improves libido, erectile function, lean mass, fat mass, mood, and energy in hypogonadal men.² ⁴ ²⁰ In women, transdermal testosterone improves sexual desire, arousal, and satisfaction.¹²

How to Diagnose Testosterone Deficiency

• Men

The American Urological Association (AUA) and the Endocrine Society recommend diagnosing testosterone deficiency based on clinical symptoms plus repeated morning total testosterone levels below ~300 ng/dL, confirmed on at least two separate occasions.²¹⁻²² Additional labs should include free testosterone, SHBG, estradiol, LH, FSH, hematocrit, PSA (baseline), and metabolic markers.

• Women

There are no universally agreed diagnostic ranges in women. Diagnosis relies on clinical symptoms plus laboratory evaluation of total and free testosterone (or calculated free), interpreted in light of the clinical picture.¹² ²³ SHBG measurement is critical because it strongly influences free testosterone levels.

Below are my recommended laboratory tests for someone concerned they may have a testosterone deficiency:

All of these tests do not need to be run every single time lab levels are monitored, but they should be checked at least on the initial labs.

Normal vs. Optimal Lab Levels

A major source of confusion in hormone therapy is the difference between “normal” laboratory reference ranges and “optimal physiologic levels,” in this case in particular with total and free testosterone.

Total vs. Free Testosterone

Total testosterone includes all testosterone that is circulating in the bloodstream. About 40–50 % is tightly bound to SHBG (inactive), ~50–60 % is loosely bound to albumin (bioavailable), and only 1–3 % is free and biologically active.¹ Like other hormones, testosterone has to be free and not bound to a protein to trigger activity in the cells of the body.

When SHBG levels are elevated, the excess SHBG binds to even more of the testosterone.  This can result in total testosterone levels in the normal range, but the free testosterone levels will be low. This is common with aging, liver disease, hyperthyroidism, or oral estrogens.²

Most outcome studies track free testosterone, because it correlates more closely with sexual function, metabolic effects, and quality-of-life outcomes than total testosterone alone.³⁻⁴ Checking only your total testosterone may not give you the whole picture.

Remember, a lab reference range reflects population averages, NOT optimal health. The reference ranges include all age groups in the population, including people that are older and with other health issues that can affect testosterone levels.

In women, testosterone therapy may be considered if the free testosterone level is <10 pg/mL and they are symptomatic. This includes women with a total testosterone in the normal reference range.

In men, testosterone therapy may be considered if the free testosterone level is <150 pg/mL and they are symptomatic. This includes men with a total testosterone level in the normal reference range ( >300 ng/dL).

Unfortunately, insurance will not normally cover testosterone therapies if the total testosterone level is in the reference range. However, there are still affordable treatments. We will discuss these in the article Testosterone Treatment Options, Monitoring and Safety.

As discussed in my book “The New Thyroid Handbook,” it’s important to check all thyroid labs when testing thyroid function. Just because the TSH is in the normal range doesn’t mean the thyroid function is normal. The same holds true for assessing testosterone function. 

Just checking total testosterone will miss many people who are suffering from a testosterone deficiency at the cellular level. They may have total testosterone levels in the normal range, but their free testosterone may be significantly low which will cause them to have symptoms of low testosterone.

Summary

Testosterone plays a vital role in the health of both men and women — influencing energy, mood, brain function, bone strength, metabolism, and sexual health. Many people experience symptoms of low testosterone even when their lab results fall within the “normal” population ranges, especially if their free testosterone is low.

Accurate diagnosis involves a thorough evaluation of symptoms and comprehensive lab testing, not just a single total testosterone measurement. Identifying and addressing suboptimal testosterone levels can significantly improve quality of life, physical health, and long-term well-being.

👉 Next: Read Part 2: Testosterone Treatment Options, Monitoring, and Safety to learn about available therapies and how they’re managed.

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