This guide covers testosterone replacement therapy for adult men with clinically low testosterone (hypogonadism). It is an educational resource — not medical advice. Always work with a qualified healthcare provider before starting or changing any treatment.
What Is Testosterone?
Testosterone is the primary male sex hormone, produced primarily by the testes. It regulates sexual function, muscle mass, bone density, fat distribution, and mood. Testosterone levels in men peak in the late teens and early 20s, then decline approximately 1% per year starting around age 30.[2]
In adult men, testosterone plays critical roles in:
- Sexual function — libido and erectile capacity
- Muscle mass and strength — promotes muscle protein synthesis
- Bone density — maintains bone mineral density
- Body composition — supports lean muscle and regulates fat distribution
- Mood and cognitive function — influences motivation, sense of well-being, and focus
- Metabolic function — affects insulin sensitivity and lipid metabolism
What Is Low T?
Low testosterone — clinically called hypogonadism — is defined as a testosterone level below normal in the presence of symptoms consistent with testosterone deficiency.[3]
There are two clinical types:
- Primary hypogonadism — the testes themselves are not producing adequate testosterone
- Secondary hypogonadism — the hypothalamus and pituitary are not signaling the testes properly
The clinical threshold most commonly used: total testosterone below 300 ng/dL on a morning blood test, confirmed on repeat testing, in the presence of symptoms.[5]
Many men with total testosterone above 300 ng/dL still have clinically low free testosterone — the portion actually available to tissues. Two key factors drive this:
- SHBG (Sex Hormone-Binding Globulin) — This protein increases with age, obesity, liver dysfunction, and certain medications. When SHBG is elevated, it binds more testosterone, leaving less free T available even when total T is normal. A man with total T of 450 ng/dL and high SHBG may have free T in the same range as a man with total T of 250 ng/dL and normal SHBG.
- Androgen Receptor Sensitivity (CAG Repeat Length) — The androgen receptor gene contains a CAG trinucleotide repeat region. Shorter CAG repeats produce a more sensitive receptor — meaning less testosterone is needed to achieve the same cellular effect. Men with longer CAG repeats may require higher testosterone levels for optimal effect, even when total T appears "normal" by standard ranges.
This is why free testosterone — not just total testosterone — must be measured. And why a knowledgeable provider looks at the whole picture: total T, free T, SHBG, and clinical symptoms together.
Symptoms of Low Testosterone
Low testosterone produces a constellation of symptoms that typically develop gradually and are often misattributed to stress or aging:[6]
Sexual Symptoms
- Reduced sexual desire (libido) — often the first noticeable change
- Decreased spontaneous erections
- Erectile dysfunction or reduced quality
Physical Symptoms
- Persistent, unexplained fatigue that doesn't improve with rest
- Increased body fat, particularly visceral (abdominal) fat
- Loss of muscle mass and strength despite exercise
- Reduced physical endurance
- Hot flashes (yes, men can get them too)
Psychological and Cognitive Symptoms
- Depressed mood or reduced sense of well-being
- Difficulty concentrating ("brain fog")
- Reduced motivation and energy
- Irritability and mood instability
If you are experiencing three or more of the symptoms above — particularly persistent fatigue, reduced libido, and changes in body composition — and they are affecting your quality of life, ask your doctor about having your testosterone checked.
How Is Low T Diagnosed?
Diagnosis requires both laboratory evidence of low testosterone AND the presence of symptoms. One without the other is not sufficient for diagnosis.[7]
The Right Laboratory Tests
Testosterone should be measured in the morning (before 10 AM) because levels follow a diurnal rhythm. A single low reading is not diagnostic — the test should be confirmed with repeat measurement on a different day.
A complete hormone workup should include:
- Total testosterone — total amount in blood
- Free testosterone — the portion available to tissues (critical)
- SHBG — protein that binds testosterone; elevated SHBG can cause low free T even with normal total T
- Estradiol — elevated estrogen can cause symptoms in men
- LH and FSH — to distinguish primary from secondary hypogonadism
- PSA — baseline before starting TRT
- CBC (Complete Blood Count) — measures red blood cells, white blood cells, platelets; critical baseline before TRT, especially hematocrit and hemoglobin
Standard blood panels capture a single moment — your testosterone level at the exact time the draw was taken. That snapshot is useful, but it doesn't show you the trend, the pattern, or the daily variation that a man experiences due to circadian rhythms, exercise, nutrition, sleep quality, stress, and alcohol use.
Salivary testosterone testing offers a different window: it measures the free, unbound testosterone fraction — the portion actually available to tissues — and it can be done at home, multiple times per week, without a lab visit.
Tracking your free testosterone weekly over several months can reveal patterns that a single blood draw will never show. You can begin to see how exercise volume, sleep quality, dietary changes, alcohol consumption, stress events, and supplemental zinc or vitamin D affect your level in real time. For a man curious about his hormonal health — whether or not he has diagnosed low T — this kind of trend data offers something blood work alone cannot: a dynamic picture of his androgen environment, and an early warning system for decline.
This is different from clinical diagnosis. Salivary testing is not a substitute for a qualified medical evaluation, and it should not be used to self-prescribe treatment. But as a complement to annual blood work, it can help a man stay ahead of the curve — observing his own trajectory before symptoms become severe enough to trigger a clinical visit.
Most men with straightforward low testosterone can be well-managed by an experienced primary care provider, endocrinologist, or men's health clinic. However, certain patterns call for a urologist specifically — providers with subspecialty training in male genitourinary and reproductive medicine who have diagnostic tools others may not.
Consider seeking a urologist if you:
- Have elevated SHBG that doesn't respond to standard treatment approaches
- Have abnormal findings on testicular exam or testicular size concerns
- Have concurrent urological conditions (BPH, prior prostate issues, urinary symptoms)
- Have a fertility goal and need coordinated hormonal management
- Have hormonal patterns that don't fit the standard picture despite symptoms
A urologist can offer advanced evaluation including detailed hormonal profiling, testicular ultrasound, and specialized reproductive hormone protocols that generalists typically do not use.
Causes of Low Testosterone
The most common cause is age-related decline — primary testicular failure associated with aging. Beyond age, the most significant modifiable cause is obesity. Fat tissue contains aromatase, which converts testosterone to estrogen, reducing free testosterone levels.[12]
Other contributing factors include:
- Type 2 diabetes and metabolic syndrome
- Obstructive sleep apnea
- Chronic kidney disease
- Opioid pain medications
- Anabolic steroid use (prior)
TRT Treatment Options
Testosterone replacement therapy restores testosterone to the normal physiological range. Several delivery methods exist, each with distinct profiles:[13]
Injectable Testosterone (Cypionate / Enanthate)
Most affordable and commonly prescribed. Administered weekly or biweekly. Produces peaks and troughs — some men experience "TRT crash" in the days before the next injection.
Topical Gels (AndroGel, Generic)
Applied daily to the skin. Provides steady-state testosterone levels and avoids peaks/troughs. Skin transfer risk — women and children must avoid contact with application site.
Clomiphene Citrate
Some doctors use clomiphene citrate as an off-label option for men who want to preserve or improve fertility while addressing testosterone deficiency. It is a selective estrogen receptor modulator (SERM) that stimulates the testes to produce more testosterone without suppressing the HP-gonadal axis. This use is considered off-label — it is not FDA-approved specifically for this purpose — and must be evaluated and recommended by a qualified healthcare provider.[14]
What to Expect on TRT
Effects develop at different rates:[15]
- Weeks 1–4: Many men notice improved energy and mood within the first few weeks
- Months 1–3: Improvements in sexual desire, energy, and well-being typically emerge
- Months 3–6: Measurable changes in body composition — reduced fat, increased lean muscle
- Months 6–12: Bone density effects and continued cognitive improvements
TRT is physiological replacement, not anabolic steroid use. The dramatic muscle-building seen in supraphysiological steroid protocols does not occur at properly prescribed doses.[16]
Risks and Side Effects
- Polycythemia — TRT increases red blood cell production. The CBC (Complete Blood Count) measures your hematocrit and hemoglobin — the concentration and total amount of red blood cells. Elevated hematocrit is the most common TRT side effect and requires dose adjustment. CBC monitoring is standard at baseline, then every 3–6 months.
- Prostate health — Testosterone does not cause prostate cancer, but can stimulate existing BPH. Baseline and ongoing PSA monitoring is standard of care.[18]
- Cardiovascular risk — Physiological-dose TRT in men without pre-existing CVD (cardiovascular disease) is not associated with increased cardiovascular risk in current evidence.[19]
- Infertility — Exogenous testosterone suppresses sperm production. Discuss hCG or clomiphene if fertility is a concern.
- Acne and skin reactions — Possible, particularly in the first months
Questions to Ask Your Doctor
- What labs are you running before I start — including free testosterone and SHBG?
- What do you consider "low" testosterone for my age and symptoms?
- What form of testosterone do you recommend and why?
- How will you monitor my hematocrit and PSA?
- What happens if I want to preserve my fertility?
- What does your follow-up schedule look like?
Find a Verified TRT Provider
TRT-Finder's directory includes verified testosterone therapy providers — filtered by city, telemedicine, and services.
Search Providers → TRT Cost Guide →Glossary of Terms
- TRT
- Testosterone Replacement Therapy — the clinical use of testosterone to treat diagnosed low testosterone (hypogonadism).
- Low T
- Common shorthand for low testosterone, clinically called hypogonadism.
- Free Testosterone
- Testosterone not bound to proteins (SHBG or albumin) — the fraction available to tissues and cells. The most clinically relevant measure for symptomatic men.
- SHBG
- Sex Hormone-Binding Globulin — a protein produced by the liver that binds testosterone, reducing the amount of free T available. Elevated SHBG is common with aging, obesity, and liver stress.
- CAG Repeat Length
- A trinucleotide repeat sequence in the androgen receptor gene. Longer repeats reduce receptor sensitivity, meaning higher testosterone may be needed for the same effect. A factor in individual TRT dosing variation.
- CBC
- Complete Blood Count — a standard lab test that measures red blood cells, white blood cells, platelets, hematocrit, and hemoglobin. Used to monitor TRT's effect on red blood cell production.
- CVD
- Cardiovascular Disease — conditions affecting the heart and blood vessels, including coronary artery disease, heart attack, and stroke.
- HPTA / HP-Gonadal Axis
- The Hypothalamic-Pituitary-Testicular Axis — the hormone signaling system that controls natural testosterone production. Exogenous testosterone suppresses this axis, reducing natural production and sperm output.
- HSDD
- Hypoactive Sexual Desire Disorder — a recognized clinical condition characterized by persistently reduced sexual desire causing personal distress. The most evidence-supported indication for testosterone therapy in women.
- BPH
- Benign Prostatic Hyperplasia — non-cancerous enlargement of the prostate gland. Testosterone can stimulate prostate tissue growth; monitoring PSA and prostate health is standard during TRT.
- PSA
- Prostate-Specific Antigen — a protein produced by the prostate gland. Elevated PSA can indicate prostate enlargement, inflammation, or (not definitively) cancer. Baseline PSA is required before starting TRT.
- Polycythemia
- An elevated red blood cell count, typically measured as hematocrit above the normal range. The most common TRT side effect; managed through dose adjustment and, in some cases, therapeutic phlebotomy.
References
- Bhasin S, et al. "Testosterone Therapy in Men with Hypogonadism." JCEM, 2018.
- Harman SM, et al. "Longitudinal Effects of Aging on Serum Total and Free Testosterone Levels." JCEM, 2001.
- Mulligan T, et al. "Prevalence of Hypogonadism in Males Aged at Least 45 Years." Int J Clin Pract, 2006.
- American Urological Association. "Evaluation and Management of Testosterone Deficiency." AUA Guideline, 2018.
- Wu FC, et al. "Identification of Late-Onset Hypogonadism." NEJM, 2010.
- Bhasin S, et al. "Testosterone Therapy in Men with Hypogonadism." JCEM, 2018.
- Cohen J, et al. "Testosterone and Obesity." Obesity Reviews, 2016.
- Bach PV, et al. "Testosterone Replacement Therapy." Med Clin N Am, 2021.
- Katz DJ, et al. "Emerging Non-Invasive Testosterone Therapies." Transl Androl Urol, 2016.
- Saad F, et al. "Effects of Testosterone on Body Composition." J Osteoporosis, 2010.
- Bhasin S, et al. "Drugs for Performance Enhancement." Med Clin N Am, 2022.
- Morgentaler A. "Testosterone and Prostate Cancer." J Urol, 2019.
- Hackett G, et al. "Testosterone and the Heart." Eur Heart J, 2018.