What is Testosterone And Why Do Men Need It?

PHYSICIAN-REVIEWED HORMONE EDUCATION

Medically reviewed by Dr. Timothy Mackey
Medical Director, NovaGenix
Updated September 2026

What testosterone does in the body

Testosterone is an androgen hormone. In men, most is produced by Leydig cells in the testes in response to luteinizing hormone from the pituitary. The hypothalamus helps regulate pituitary signaling. Learn more about how men produce testosterone through brain signals and testicular cells. Testosterone is also present in women, usually at much lower concentrations.

It contributes to sexual development, libido, muscle and bone maintenance, and red-blood-cell production. The reproductive system depends on coordinated hormone signals. A hormone's normal biological role should not be read as a list of benefits guaranteed by taking more of it.

Normal testosterone and TRT affect fertility differently

Testosterone within the testes helps support sperm production. External testosterone can suppress the signals needed for that process and can markedly reduce sperm production. Tell the clinician about current or future fertility plans before considering replacement therapy. Our guide to TRT and its effects on sperm production and fertility explains this distinction in more detail.

hCG is a different medicine that stimulates testicular hormone production in selected circumstances; it is not a testosterone formulation or a guarantee of fertility preservation. Over-the-counter “testosterone boosters” are not interchangeable with prescribed treatment.

How is low testosterone diagnosed?

Reduced sexual desire, fewer spontaneous erections, fatigue and changes in body composition may warrant assessment, but none proves testosterone deficiency alone. Similar symptoms can have other causes.

The Endocrine Society guideline calls for compatible symptoms and consistently low testosterone, confirmed with separate morning measurements. Additional tests help clarify the underlying cause. See causes of low testosterone and how doctors evaluate them. Free testosterone is useful in selected situations rather than being required for every person.

Aging does not automatically mean hypogonadism, and the earlier claim that half of men have “andropause” by their forties should not guide decisions. Reversible contributors, medicines and other health conditions need consideration. Our testosterone levels by age reference explains how age-related patterns differ from an individual diagnosis.

What replacement therapy can and cannot do

Appropriately selected patients may experience benefits, but responses differ. TRT does not guarantee better energy, relationships or overall health, and should not be presented as prevention for cardiovascular or metabolic disease.

Monitoring should assess symptom response and adverse effects, including hematocrit and blood-pressure changes, with prostate assessment when appropriate. Supervision can help manage risk; it cannot make treatment risk-free. Effects develop over different timeframes, and persistent symptoms deserve reassessment rather than an automatic dose increase. Explore our testosterone replacement therapy overview for evaluation, treatment options and monitoring.

Discuss an evaluation in Jupiter

NovaGenix's Medical Director is Timothy Mackey, D.O. A consultation can review symptoms, available laboratory results and whether further evaluation or treatment is appropriate.

NovaGenix's $125 initial male hormone panel includes physician lab review or consultation. All laboratory testing, including follow-up labs, is billed separately from the TRT program. Patients may supply their own results for review or use the clinic's physician account with Labcorp for affordable lab rates.

NovaGenix is located at 609 N Hepburn Ave, Suite 106, Jupiter, FL 33458. Request a physician evaluation or call 561-277-8260.