Reviewed by TRT Index Editorial Team · Last reviewed October 1, 2026
What is testosterone replacement therapy?
TRT is a medically supervised treatment that restores testosterone to a healthy range in men whose natural production has dropped below normal. It's one of the most studied hormone therapies in modern medicine - and one of the most misunderstood.
Answer first: what is TRT?
TRT is testosterone replacement therapy: a clinician-supervised treatment for men with confirmed low testosterone and compatible symptoms. A responsible TRT plan starts with diagnostic labs, reviews risks and fertility goals, chooses a delivery method, and continues with follow-up bloodwork.
Confirmed by two separate morning blood draws showing low total testosterone, plus documented symptoms. The AUA uses 300 ng/dL as its cutoff; the Endocrine Society uses 264 ng/dL.
Intramuscular or subcutaneous injections, topical gels, long-acting pellets, oral undecanoate, and transdermal patches.
TRT is generally a long-term therapy. Stopping typically returns testosterone to its prior low baseline within weeks.
Who TRT is for
TRT is indicated for men diagnosed with hypogonadism - a clinical condition where the body produces insufficient testosterone. The Endocrine Society and American Urological Association both recommend confirming low testosterone with two separate morning blood tests, since levels fluctuate significantly through the day and a single reading can be misleading.
The two guidelines draw the line in slightly different places. The AUA treats a total testosterone below 300 ng/dL as low. The Endocrine Society uses 264 ng/dL, the lower limit of normal for standardized lab assays, and asks for a fasting morning sample. Either way, one low number on its own is not a diagnosis.
Low testosterone often shows up as a cluster of symptoms rather than a single complaint:
- Persistently low energy or motivation that doesn't improve with rest
- Reduced libido, erectile dysfunction, or decreased spontaneous erections
- Loss of muscle mass or strength despite consistent training
- Increased body fat, especially abdominal
- Mood changes - irritability, depression, mental fog
- Poor sleep, hot flashes, or night sweats
Symptoms alone aren't enough. A responsible clinic will rule out other causes first (sleep apnea, thyroid dysfunction, depression, medication side effects, chronic illness) before starting treatment. If your provider offers TRT after a single phone call and no labs, that's a red flag.
How the main delivery methods compare
No single form is "best" - the right choice depends on your schedule, needle tolerance, insurance coverage, and how your body metabolizes testosterone.
| Form | Frequency | Pros | Trade-offs |
|---|---|---|---|
| IM or SubQ injection (cypionate/enanthate) | Weekly or twice-weekly | Cheapest, most stable levels, widely prescribed | Self-injection required; some men get peaks and troughs |
| Topical gel / cream | Daily | No needles; steady daily dosing | Transfer risk to partners/children; skin absorption varies |
| Subcutaneous pellets | Every 3-6 months | Set-and-forget; very stable blood levels | In-office minor procedure; dose can't be adjusted mid-cycle |
| Oral undecanoate (Jatenzo, Kyzatrex) | Twice daily with food | No needles, no skin transfer | Expensive, must be taken with dietary fat |
| Transdermal patch | Daily | Simple application | Frequent skin irritation; less commonly prescribed today |
What TRT actually does (and doesn't do)
Guidelines aim for the middle of the normal range rather than the top of it: the AUA guideline suggests 450-600 ng/dL. Some clinics target higher levels, so ask what range a provider aims for and why. When testosterone is restored to a mid-normal range, the improvements men most reliably report in controlled studies are:
- Increased libido and frequency of spontaneous erections
- Improved mood and reduced depressive symptoms
- Better lean-mass-to-fat-mass ratio over 6-12 months
- Modest strength gains
- Improved bone mineral density with long-term therapy
What TRT won't reliably do: turn an average body into a bodybuilder's, dramatically improve cognition in men whose testosterone was already normal, or serve as a substitute for sleep, diet, or exercise. Clinics that pitch TRT as a performance-enhancing fountain of youth are overpromising.
Risks and side effects
Most healthy men tolerate TRT well with appropriate monitoring, but real risks exist:
- Elevated hematocrit (thickened blood). The most common side effect. Periodic blood donations or dose adjustment typically manage it.
- Fertility suppression. Exogenous testosterone signals the testes to stop producing sperm. Men who want to preserve fertility should discuss HCG, enclomiphene, or sperm banking before starting.
- Acne and oily skin. Usually settles within a few months.
- Gynecomastia (breast tissue growth). Caused by testosterone converting to estrogen; managed with dose adjustment or aromatase inhibitors when clinically needed.
- Sleep apnea worsening. TRT can aggravate untreated sleep apnea - worth screening for before starting.
- Cardiovascular considerations. The TRAVERSE trial (2023) found no increased major cardiovascular events in men with hypogonadism on TRT, but the picture remains nuanced for men with pre-existing heart disease.
- Prostate. TRT doesn't cause prostate cancer, but it can accelerate growth of an existing cancer. PSA is monitored routinely.
What good monitoring looks like
The therapy is safe to the extent it's monitored. A reasonable baseline and follow-up protocol includes:
- Baseline labs: total testosterone, free testosterone, SHBG, estradiol (sensitive assay), LH, FSH, CBC (for hematocrit), PSA, metabolic panel
- Symptom and blood pressure check
- Follow-up labs after starting or changing a dose: the Endocrine Society suggests rechecking testosterone 3 to 6 months after starting, and many clinics check sooner, around 6 to 8 weeks
- Labs every 6 to 12 months once stable, with PSA and hematocrit checked at least annually
Our guide to what labs a TRT clinic should order explains what each marker is for.
If a clinic doesn't order labs before prescribing, skips follow-up bloodwork, or refuses to adjust your dose based on how you feel and what your labs show, keep looking.
Questions worth asking before you start
- What labs will you run before prescribing, and how often are follow-ups?
- What's your protocol for men who want to preserve fertility?
- How do you handle rising hematocrit?
- Who do I call after hours if I have a reaction?
- What's the total all-in monthly cost, including labs and consultations?
- Am I locked into a long-term contract, or can I stop any time?
For a longer checklist, see questions to ask before starting TRT, and use the TRT cost guide to compare all-in prices.
Sources
- Bhasin S, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018;103(5):1715-1744.
- Mulhall JP, et al. Evaluation and Management of Testosterone Deficiency: AUA Guideline. J Urol. 2018;200(2):423-432.
- Lincoff AM, et al. Cardiovascular Safety of Testosterone-Replacement Therapy (TRAVERSE). N Engl J Med. 2023;389:107-117.
Medical disclaimer: This article is for general information only and is not medical advice. Hormone therapy decisions should be made with a licensed clinician who knows your full medical history.
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