Testosterone is one of the most talked‑about hormones yet also one of the most misunderstood. As the primary male sex hormone, it plays a crucial role in fetal development, puberty and adulthood, but it is present in women as well and contributes to overall health. Media stories and marketing campaigns sometimes oversimplify or sensationalize testosterone’s role, leading to confusion about what it does, why levels fluctuate and when therapy is appropriate. This article gathers current evidence and clinical guidance to present critical facts about testosterone that everyone should know. Understanding these facts can help individuals make informed decisions about testing, lifestyle choices and potential treatment.

What Is Testosterone?

Testosterone is a steroid hormone produced mainly by the testicles in males and to a lesser degree by the ovaries in females and the adrenal glands in both sexes. While testosterone levels are naturally much higher in males, it is an important hormone for females, too, contributing to bone and muscle strength, libido and overall well‑being. Testosterone is part of the androgen family, meaning it stimulates the development of male characteristics. In the body, most testosterone binds to proteins such as sex hormone‑binding globulin (SHBG) and albumin; only a small fraction circulates as free testosterone, which is biologically active.

Natural Testosterone vs. Anabolic Steroids

Natural testosterone qualifies as an anabolic‑androgenic steroid because it promotes tissue growth and male characteristics. However, when people refer to “anabolic steroids,” they usually mean synthetic variations taken in supraphysiologic doses to enhance athletic performance or appearance. Therapeutic testosterone used to treat low levels is administered under medical supervision and aims to restore hormone concentrations to the normal physiologic range.

How Testosterone Functions Across Life Stages

Fetal Development

Around the seventh week of pregnancy, the presence of a Y chromosome triggers the formation of the testicles in male fetuses. Sertoli cells produce a Müllerian‑inhibiting substance that prevents female reproductive structures from forming. Leydig cells then produce testosterone, which supports the development of the male urogenital tract and external genitalia. Testosterone converts to dihydrotestosterone (DHT) in peripheral tissues to form the prostate and penile structures. In cases where a male child is born with undescended but normal testes, testosterone therapy can assist in testicular descent.

Puberty

During puberty, testosterone drives many of the physical changes associated with male maturation. It increases height, deepens the voice, stimulates pubic and facial hair growth, enlarges the penis and testes, and boosts libido. Testosterone also promotes skeletal muscle growth and accelerates bone maturation. In puberty, the hypothalamic–pituitary–gonadal axis becomes active: the hypothalamus releases gonadotropin‑releasing hormone (GnRH), which prompts the pituitary to release luteinizing hormone (LH) and follicle‑stimulating hormone (FSH); LH then stimulates the Leydig cells in the testes to produce testosterone.

Adulthood

In adult males, testosterone maintains sperm production, supports bone and muscle strength, signals the production of red blood cells and enhances libido and mood. The hormone stimulates protein synthesis, helping to preserve muscle mass. Testosterone also stimulates erythropoiesis (red blood cell production), resulting in higher hematocrit levels in males compared to females. For adult females, testosterone contributes to libido and is largely converted to estradiol (a form of estrogen).

Natural Decline With Age

Testosterone levels typically peak in a man’s late teens to early 20s and decline gradually thereafter. Men may lose approximately 1 % of their testosterone per year after age 40. This decline is part of normal aging but may be exacerbated by chronic conditions such as obesity and Type 2 diabetes. Low testosterone in older adults is sometimes referred to as “andropause” or “male menopause,” though the term is misleading because it implies a universal deficiency where none exists.

What Causes Low Testosterone?

Low testosterone, or hypogonadism, occurs when the body doesn’t produce enough testosterone. Causes include:

• Testicular damage: injury, infection (e.g., mumps) or undescended testes.
  
• Pituitary gland dysfunction: failure to signal the testes to produce testosterone.
  
• Genetic conditions: such as Klinefelter syndrome or Kallmann syndrome.
  
• Obesity and chronic diseases: including Type 2 diabetes and hemochromatosis.
  
• Tumors and some medications: cancer treatments, steroid therapy and other medications can suppress testosterone production.
  
• Age‑related decline: part of natural aging, accelerated in individuals with metabolic disorders or obesity.
  

In women, testosterone levels decline gradually until menopause and can be affected by oral contraceptives, steroid therapy or pituitary disorders.

Symptoms of Low Testosterone

Symptoms vary by age and severity. In adult males, low testosterone can cause:

• Reduced libido and erectile dysfunction.
  
• Fatigue, low energy and mood changes.
  
• Difficulties concentrating and memory issues.
  
• Increased body fat and reduced muscle mass and strength.
  
• Swollen or tender breasts and loss of body hair.
  
• Infertility and decreased bone density.
  

In children, signs include delayed puberty, slow growth spurts, and limited body hair development. Women may experience low libido; however, symptoms in females are often subtle and less recognized.

Testing and Diagnosing Low Testosterone

Doctors usually order a morning total testosterone blood test because levels are highest early in the day. If the first test shows low levels, a second test confirms the result, and providers may check FSH, LH and prolactin to determine whether the cause is testicular (primary) or pituitary/hypothalamic (secondary). Normal testosterone ranges vary by age and laboratory, but typical adult male levels fall between approximately 300–1,000 ng/dL.

Effects of High Testosterone

Elevated testosterone can be natural or exogenous. Natural hyperandrogenism may result from adrenal or ovarian tumors or conditions like polycystic ovary syndrome (PCOS). Exogenous excess comes from anabolic steroid misuse or taking too much therapeutic testosterone. Excess testosterone can lead to mood swings, acne, increased red blood cells, sleep apnea, liver abnormalities, infertility and testicular shrinkage. Women with high androgen levels may develop acne, hirsutism, male‑pattern baldness or menstrual irregularities.

Testosterone in Women: Not Just a Male Hormone

Though testosterone is often called a male hormone, it is essential for women. Ovaries and adrenal glands produce small amounts of testosterone, which helps maintain bone mass, muscle strength and libido. Some testosterone converts to estradiol, the primary female sex hormone. Women with abnormally low testosterone may experience reduced libido, fatigue and mood changes, but there is no widely accepted threshold for “low” levels in women. Clinicians tailor treatment to symptoms and carefully monitor dosing to avoid virilization.

The Relationship Between Testosterone and Health Conditions

Metabolic Health

Low testosterone is associated with metabolic syndrome, obesity and Type 2 diabetes. MenMD notes that nearly 40 % of men aged 45 and older have some degree of hypogonadism. Obesity can suppress testosterone levels, which in turn can exacerbate weight gain and insulin resistance—a vicious cycle. Lifestyle modifications such as weight loss, regular exercise and stress reduction can improve testosterone levels and metabolic health.

Bone and Muscle Health

Testosterone helps maintain bone mineral density and muscle mass. Low levels increase the risk of osteoporosis and fractures. In puberty, testosterone stimulates growth at the epiphyseal plate and later helps close the growth plates to terminate growth. It also promotes protein synthesis in muscles, making it critical for maintaining strength.

Red Blood Cells

Testosterone stimulates erythropoiesis, the production of red blood cells, which helps explain why men generally have higher hematocrit levels than women. Men with low testosterone may develop anemia, while excessive testosterone can increase red cell counts dangerously, leading to thickened blood and elevated risk of clotting. Monitoring hematocrit is an important part of testosterone therapy.

Mood and Cognition

Low testosterone has been linked to depressive symptoms, irritability and decreased motivation. Adequate levels often correlate with improved mood and cognitive function. In women, falling estrogen (and testosterone) levels contribute to “brain fog” during menopause; estrogen replacement can help support cognition.

Sexual Function and Fertility

Testosterone maintains libido and supports normal erectile function in men. In women, it contributes to sexual arousal. However, exogenous testosterone can suppress spermatogenesis by inhibiting the hypothalamic‑pituitary‑gonadal axis, leading to reduced sperm count. Fertility can often be preserved by using adjunct medications like clomiphene or hCG to stimulate natural testosterone and sperm production. Women undergoing in vitro fertilization or those with PCOS may require regulation of androgen levels for optimal fertility.

Therapeutic Testosterone: Forms and Innovations

Traditional Forms

Therapeutic testosterone comes in several formulations:

• Injectable testosterone cypionate or enanthate: Administered every one to two weeks or in smaller, more frequent doses (microdosing) to maintain steady levels.
  
• Transdermal patches and gels: Applied daily to deliver testosterone through the skin. Modern gels reduce transfer risk and skin irritation.
  
• Implantable pellets: Small pellets inserted under the skin release hormone over several months. Newer pellets are smaller and easier to insert.
  
• Nasal gels and buccal tablets: Applied inside the nose or adhered to the gums for quick absorption.
  
• Oral testosterone: Recent formulations like testosterone undecanoate use lymphatic absorption to bypass the liver, achieving high bioavailability.
  

Emerging Technologies

Research continues to improve testosterone delivery. Microdosing protocols administer smaller amounts more frequently to mimic natural fluctuations and reduce side effects. Hydrogel microbeads, created through core‑shell spherification, encapsulate testosterone in biodegradable microspheres that release the hormone slowly after a single injection. Early data suggest this method can extend hormone half‑life from hours to 10 days or more.

Artificial intelligence (AI) and telehealth are transforming testosterone care. AI‑driven algorithms analyze hormone levels, genetics and lifestyle factors to recommend personalized dosing strategies, while telehealth platforms provide remote consultations, at‑home lab kits and medication delivery. These innovations improve accessibility and adherence, especially for patients who prefer to avoid frequent clinic visits.

Safety and Side Effects

Common side effects of testosterone therapy include acne, oily skin, fluid retention, breast enlargement, decreased sperm production and irritability. Increases in hematocrit and prostate‑specific antigen (PSA) levels may occur, requiring regular monitoring. People with prostate or breast cancer, untreated sleep apnea, severe heart failure or high hematocrit should not use testosterone therapy.

The U.S. Food and Drug Administration (FDA) revised testosterone product labels in 2025. After the TRAVERSE trial found no increase in major cardiovascular events among men receiving TRT, the FDA removed the boxed warning about heart attacks and strokes but added warnings about elevated blood pressure. Labels also maintain the limitation that TRT should only be used for men with medically confirmed low testosterone.

Lifestyle Strategies to Support Healthy Testosterone Levels

In many cases, lifestyle changes can boost or maintain testosterone levels without medication. Evidence‑based recommendations include:

• Maintaining a healthy weight: Excess body fat, especially visceral fat, increases aromatase activity (conversion of testosterone to estrogen) and suppresses testosterone production.
  
• Regular exercise: Both aerobic and resistance training support hormone balance and muscle mass.
  
• Adequate sleep: Poor sleep disrupts hormone synthesis and release. Aim for 7–9 hours per night.
  
• Balanced diet: Foods rich in zinc, vitamin D and healthy fats support testosterone production. Limiting sugar and processed foods can prevent insulin resistance.
  
• Stress management: Chronic stress elevates cortisol, which can suppress the hypothalamic–pituitary–gonadal axis and lower testosterone levels.
  

Key Takeaways

• Testosterone is produced by the gonads and adrenal glands, plays vital roles across life stages and is essential for both men and women.
  
• Natural testosterone is an anabolic‑androgenic steroid, but therapeutic use is distinct from anabolic steroid abuse.
  
• Causes of low testosterone include testicular damage, pituitary dysfunction, genetic conditions, chronic diseases, certain medications and aging.
  
• Symptoms of low testosterone range from reduced libido and fatigue to increased body fat, mood changes and cognitive difficulties.
  
• Diagnosis requires morning blood tests and possibly evaluations of LH and FSH to determine primary vs. secondary hypogonadism.
  
• Therapeutic testosterone comes in various delivery forms and continues to evolve with technologies like microdosing, microbeads and AI personalization.
  
• Lifestyle interventions—weight management, exercise, adequate sleep, balanced nutrition and stress reduction—are foundational for maintaining healthy testosterone levels.
  
• Safety requires regular monitoring of testosterone levels, hematocrit, PSA and side effects; certain health conditions preclude therapy.
  

Frequently Asked Questions (FAQs)

What is a normal testosterone level for men?

Normal testosterone ranges vary by age and laboratory, but for adult men the typical reference range is approximately 300–1,000 ng/dL. Providers interpret results relative to specific lab standards and clinical symptoms. Levels naturally decline with age.

How do I know if I have low testosterone?

Symptoms include reduced libido, erectile dysfunction, fatigue, mood changes, increased body fat, decreased muscle mass and low bone density. A diagnosis requires one or more morning blood tests and evaluation by a healthcare provider.

Can women have low testosterone?

Yes. Women produce testosterone and can experience low levels, resulting in decreased libido, fatigue and mood changes. Because there are no widely accepted “normal” ranges for women, treatment decisions are based on symptoms and blood levels.

Does testosterone therapy cause prostate cancer?

Evidence does not support a direct link between therapeutic testosterone and prostate cancer; PSA increases after TRT are minimal and not clinically significant. Routine prostate screenings remain important.

Are over-the-counter testosterone boosters effective?

There is limited evidence that over-the-counter supplements improve low testosterone symptoms. True hormone therapy requires clinical evaluation and monitoring.

Can testosterone therapy improve mood and energy?

Yes. Restoring testosterone to normal levels often improves mood, energy and cognitive function. However, results vary by individual, and therapy should only be pursued when medically indicated.

Will testosterone therapy make me infertile?

Testosterone therapy can suppress sperm production, but fertility can often be preserved with adjunct medications such as clomiphene or hCG. Discuss fertility goals with your provider before starting therapy.

How long should I stay on testosterone therapy?

TRT is usually a long-term therapy. Providers monitor hormone levels and side effects regularly. Patients may stop therapy if symptoms resolve, side effects become burdensome or new health issues arise. Always consult your doctor before making changes.