TRT Basics: What Testosterone Replacement Therapy Actually Involves
Testosterone replacement therapy (TRT) is a prescription medical treatment that raises a man's testosterone back into the normal range when it is both clinically low and causing symptoms. It is delivered through injections, gels, patches, or pellets, requires diagnosis confirmed by bloodwork, and depends on ongoing lab monitoring by a licensed clinician. In the US, testosterone is a Schedule III controlled substance, so it cannot legally be obtained or used without a prescription.
What Is TRT?
TRT involves administering exogenous (externally supplied) testosterone to restore serum testosterone to the normal physiologic range in men with clinically diagnosed hypogonadism, which is the medical term for the body not producing enough testosterone. The goal is not to push levels above normal for performance; it is to correct a confirmed deficiency that is causing symptoms.
Two things are essential to state up front. First, testosterone is a Schedule III controlled substance in the United States, which means it requires a prescription from a licensed provider and cannot legally be sourced without one. Second, this article is education, not medical advice or a diagnosis. The decision to start TRT belongs to you and a qualified clinician who is accountable for your care.
Who Is TRT For?
Diagnosis requires two things together, per Endocrine Society guidance: symptoms consistent with testosterone deficiency, and confirmed low serum testosterone on laboratory testing.
The Endocrine Society defines low total testosterone as below approximately 264 ng/dL (9.2 nmol/L), measured between roughly 7:00 and 11:00 AM in a fasting state, and a single low result is not sufficient. Diagnosis generally requires confirmation on at least two separate morning measurements, because testosterone fluctuates and a one-off reading can mislead.
Symptoms that prompt a conversation with a doctor (not a self-diagnosis) include decreased sexual desire, fatigue and low energy, mood changes, decreased muscle mass and strength, increased body fat, and difficulty concentrating. Every one of these has multiple possible causes, which is exactly why labs are mandatory. The companion article on signs of low testosterone covers this checklist in more depth, but the principle holds: symptoms raise the question, labs answer it.
How TRT Works
When testosterone is low and symptomatic, replacing it can improve the symptoms tied to the deficiency. Because the biologically active fraction of testosterone matters, clinicians sometimes look at free testosterone in addition to total, especially when total is borderline; the difference between those two numbers is explained in free vs total testosterone.
One important physiologic point: supplying testosterone externally signals the brain to reduce its own production. The hypothalamic-pituitary-gonadal axis detects adequate testosterone and dials down the hormones (LH and FSH) that drive the testes, which is why TRT suppresses natural production and can affect fertility. That tradeoff is significant enough that fertility planning should happen before starting, not after.
Delivery Methods Compared
TRT can be delivered several ways, and the main difference between them is the tradeoff between convenience and how stable your hormone levels stay. The table below is educational; your clinician selects the route and sets the dose.
| Delivery method | Convenience | Level stability | Monitoring and practical notes |
|---|---|---|---|
| Intramuscular injection | Moderate (weekly or twice-weekly) | Good; some peak-trough swing | Most common US route; flexible dosing; standard lab monitoring |
| Subcutaneous injection | Moderate; smaller needles | Good; often smoother peaks | Increasingly used; some evidence of lower peaks than IM |
| Transdermal gel | High; daily application | Steady if applied consistently | Daily use; risk of skin-to-skin transfer to others; absorption varies |
| Skin patch | High; daily | Steady | Daily use; skin irritation is common |
| Implanted pellets | Very high; months per insertion | Very steady once placed | Requires minor in-office procedure; dose cannot be quickly adjusted |
No single method is best for everyone. Injections offer the most dose flexibility; pellets offer the least day-to-day hassle but the least adjustability; gels and patches avoid needles but require daily diligence and, for gels, care around transfer to partners or children.
Dosing and Frequency, Briefly
Injection frequency is its own decision and affects how steady your levels feel. Once-weekly is simplest but produces larger swings; twice-weekly is the most common clinical approach and tends to smooth peaks and troughs; daily microdosing is the steadiest but the most demanding. Standard doses reported in the literature are commonly in the range of 100 to 200 mg per week, titrated to labs, but these are typical clinician-managed ranges, not a recommendation, and your clinician sets your dose. The full breakdown lives in TRT dosing frequency.
The Monitoring TRT Requires
This is the part that makes TRT a managed therapy rather than a one-time prescription. Before starting, clinicians typically establish a baseline: total testosterone (confirmed on a repeat morning draw), free testosterone if total is borderline, LH and FSH to distinguish the type of hypogonadism, estradiol on a sensitive assay, hematocrit and a complete blood count, and PSA where age or clinical factors indicate.
Follow-up labs commonly come around 6 to 8 weeks after initiation, then every 3 to 6 months during the first year, then at least annually if stable. Hematocrit gets particular attention because testosterone stimulates red blood cell production, and rising hematocrit thickens the blood. The full panel and rationale are covered in TRT bloodwork and labs, and the most-watched risk is detailed in TRT side effects and how they're managed.
What to Realistically Expect
In men with diagnosed hypogonadism, randomized trials show TRT can increase lean mass and decrease fat mass, typically on the order of a few kilograms of lean mass over 12 months when levels are restored to normal, with resistance training amplifying that response. In men with already-normal testosterone, the off-label "optimization" use case lacks robust evidence for body-composition benefit. In short: TRT corrects a deficiency well, but it is not a shortcut to a physique, and diet and training remain primary even on therapy.
Where Myo Fits
TRT is a long-haul protocol built on injections and labs, which makes structured tracking genuinely useful. Myo, an iOS app by PixelPort LLC, logs every injection, the site used, and the date, maps your injection sites so rotation actually happens, and trends lab values like testosterone, estradiol, and hematocrit over time alongside body composition. That is exactly the kind of trend data TRT decisions are made on, and it gives you and your prescriber a clean record for follow-up visits. The same dose-and-site logging discipline is described for GLP-1 users in how to track your GLP-1 injections. Myo is a tracking and education tool only; it does not prescribe, source, or recommend doses.
References
Endocrine Society: Testosterone Therapy Clinical Practice Guideline Defines diagnostic thresholds (total testosterone below ~264 ng/dL on morning fasting measurement), confirmation requirements, and monitoring recommendations for TRT. https://www.endocrine.org/clinical-practice-guidelines/testosterone-therapy
Endocrine Society: Hypogonadism Patient Library Patient-facing overview of hypogonadism symptoms, diagnosis, and management. https://www.endocrine.org/patient-engagement/endocrine-library/hypogonadism
FDA Testosterone Prescribing Information (2022) Label information for injectable testosterone, including controlled-substance status and monitoring guidance. https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/216318s000lbl.pdf
ASH Blood Advances: Drug-Induced Erythrocytosis (2025) Meta-analysis quantifying the increased risk of polycythemia (elevated hematocrit) with testosterone therapy. https://ashpublications.org/bloodadvances/article/9/9/2108/535485/Diagnosis-management-and-outcomes-of-drug-induced
Frequently asked questions
What is TRT and how does it work?
Testosterone replacement therapy (TRT) is a prescription medical treatment that delivers exogenous testosterone to raise a man's serum testosterone back into the normal physiologic range when it is clinically low. It works by supplementing the hormone the body is no longer producing in adequate amounts, which can improve symptoms tied to deficiency such as low libido, fatigue, and loss of muscle mass. In the US, testosterone is a Schedule III controlled substance and can only be obtained with a prescription from a licensed clinician after proper diagnosis. It is a managed therapy with ongoing monitoring, not a casual supplement.
Who is a candidate for TRT?
Candidates are typically men with both symptoms consistent with testosterone deficiency and confirmed low testosterone on laboratory testing. The Endocrine Society defines low total testosterone as below roughly 264 ng/dL on a morning, fasting measurement, and requires confirmation on at least two separate occasions before diagnosis. Symptoms alone are not enough, because fatigue, low libido, and mood changes have many possible causes. A licensed clinician makes the determination after labs and a full history; this article cannot diagnose anyone.
How is testosterone replacement delivered?
Common delivery methods include intramuscular or subcutaneous injections (testosterone cypionate or enanthate), transdermal gels, skin patches, and implanted pellets. Injections are the most common in the US and offer dose flexibility; gels are convenient but require care to avoid transferring testosterone to others by skin contact; pellets provide months of steady levels but require a minor in-office procedure. Each route trades off convenience against how stable hormone levels stay, and the choice is made with your clinician based on your labs, lifestyle, and preferences.
Is TRT safe long-term?
When properly prescribed and monitored for diagnosed hypogonadism, TRT is generally considered manageable, but it carries real risks that require ongoing oversight, including rising hematocrit (thicker blood), changes in estrogen, fertility suppression, and effects relevant to prostate health. The Endocrine Society guidelines call for regular bloodwork to catch these early. Long-term safety depends heavily on appropriate candidate selection and monitoring; it is not risk-free, and using testosterone without a prescription or medical supervision is both unsafe and illegal.
What does TRT monitoring involve?
Monitoring typically includes baseline and follow-up bloodwork covering total and free testosterone, estradiol, hematocrit and a complete blood count, and PSA where age or risk indicates it. Labs are commonly drawn around 6 to 8 weeks after starting, then every 3 to 6 months in the first year, then at least annually if stable, with hematocrit watched closely throughout. Your clinician uses these trends to adjust the dose or route. Consistent monitoring is the part of TRT that makes it a managed therapy rather than a set-and-forget prescription.
Keep reading
TRT Dosing Frequency: Weekly vs Twice-Weekly vs Daily Microdose
TRT dosing frequency: how weekly, twice-weekly, and daily microdosing affect testosterone stability and side effects, and why your clinician sets the schedule.
Signs of Low Testosterone (and What Actually Confirms It)
Signs of low testosterone: fatigue, low libido, mood and strength changes, and why symptoms alone don't confirm it. What labs actually diagnose low T.
TRT Bloodwork: The Labs That Get Monitored and Why
TRT bloodwork explained: total and free testosterone, estradiol, hematocrit, PSA, and lipids, what each marker means, and how often they get checked.