TRT 101: A Plain-English Guide to Testosterone Replacement Therapy

Testosterone replacement therapy (TRT) is the administration of exogenous testosterone — typically by intramuscular or subcutaneous injection, less commonly via gel, cream, patch, or pellet — to men whose endogenous production is clinically inadequate. The goal is restoration of total testosterone to a healthy reference range, paired with relief of the symptoms that prompted treatment in the first place.

It is not bodybuilding. It is not steroid abuse. A correctly-dosed TRT protocol produces total T levels that are well within what a healthy 25-year-old would naturally make. The medical literature on long-term, responsibly-dosed TRT in clinically deficient men is — as of 2026 — broadly favorable on safety and convincingly positive on quality of life.

The classic candidate has two things: confirmed low testosterone on two morning serum draws (generally < 300 ng/dL, though thresholds vary by lab and clinician) AND symptoms consistent with low T (fatigue, low libido, erectile dysfunction, depressed mood, loss of muscle mass, brain fog, sleep disturbance).

Without symptoms, low numbers alone are debatable as an indication. Without low numbers, symptoms alone are rarely treated with TRT. The combination is what justifies starting.

Before beginning, a competent clinician will rule out reversible causes: untreated hypothyroidism, hyperprolactinemia, sleep apnea, severe obesity, opioid use, anabolic steroid withdrawal. Some of these — especially obesity and sleep apnea — can resolve much of the apparent hypogonadism without TRT.

Injectable testosterone esters dominate TRT in the US. The two most common are cypionate (half-life ~8 days) and enanthate (half-life ~5–7 days). They behave essentially identically in practice — pick one based on what your pharmacy stocks.

Dosing typically starts at 100–200 mg per week, divided into one, two, or three injections. More frequent injections (twice weekly, every-3.5-day, or daily subcutaneous micro-doses) flatten the peak-trough swing, which most men tolerate better. Less frequent (once weekly) is operationally simpler but produces a more pronounced peak-to-trough cycle.

Gels and creams produce smoother daily levels but require careful skin contact precautions (children, partners), and topical testosterone produces dramatically higher DHT than injections. Pellets last 3–6 months but commit you to whatever dose was implanted. Sublingual lozenges are uncommon. Oral testosterone undecanoate (Jatenzo) exists but is expensive and finicky.

Most men on injectable protocols eventually settle into either once-weekly or twice-weekly dosing, with the latter slightly preferred for managing estradiol and hematocrit.

A comprehensive baseline before starting TRT should include:

• Total testosterone — on two morning draws, ideally a week apart • Free testosterone (calculated via Vermeulen is fine) • SHBG — to interpret free T • Estradiol — sensitive (LC-MS/MS) assay if possible • LH and FSH — to differentiate primary from secondary hypogonadism • Complete blood count — baseline hematocrit • Comprehensive metabolic panel — liver, kidney, glucose • Lipid panel • PSA — mandatory for men over 40 or with family history • Vitamin D, ferritin, B12 — common deficiencies that mimic low T • TSH and free T4 — to rule out thyroid disease

Follow-ups at 3, 6, and 12 months should re-check total T, free T, SHBG, estradiol, hematocrit, and PSA at minimum. Past 12 months, annual labs are usually sufficient unless something changes.

Realistic improvements within 3 months: energy, libido, mood, sleep quality, mental clarity. These tend to come on within weeks for some men, slower for others.

Realistic improvements within 6–12 months: lean mass (slow, modest unless training hard), fat distribution, erectile function, motivation.

Slow or partial improvements: depression (TRT can help but isn't a depression treatment), low motivation that has psychological roots, partner-relationship issues attributed to libido. These often require additional intervention beyond labs.

Not realistic: 25-year-old performance at 50, eliminating all fatigue regardless of sleep or diet, replacing the work of a workout program.

Most TRT side effects are manageable with monitoring and adjustment.

Polycythemia (high hematocrit): the single most consistent measurable side effect. Affects 25–40% of men on injectable TRT within a year. Managed via dose splitting, dose reduction, hydration, or therapeutic phlebotomy. Above HCT 54% warrants intervention.

Estradiol shifts: testosterone aromatizes to estradiol, especially in body fat. Both high and low E2 cause problems. Address upstream first (lower dose, lose body fat) before reaching for aromatase inhibitors.

Acne, oily skin, scalp itching: common in the first 1–3 months, usually settles. Sometimes persistent at high doses.

Mood and sleep disturbances: usually transient as your body re-equilibrates.

Fertility suppression: FSH and LH crash on TRT, sperm production stops in most men within 3–6 months. Reversible for most after stopping, but not all, and not always quickly. If kids are planned, use hCG alongside TRT.

Testicular atrophy: visible shrinkage from suppressed LH. Cosmetic only — hCG can preserve size if it matters to you.

Prostate effects: TRT does not cause prostate cancer but can accelerate growth of pre-existing cancer. PSA monitoring is mandatory.

1. Crushing estradiol with aromatase inhibitors. Causes joint pain, bone loss, mood disturbance, low libido — and is rarely necessary on injectable TRT.

2. Chasing labs instead of symptoms. Numbers exist to inform decisions, not drive them. A man feeling great with total T of 750 doesn't need to push to 1,200.

3. Ignoring hematocrit. It rises slowly, then bites suddenly. Donate blood proactively or split your dose before HCT climbs past 52%.

4. Choosing topical T without thinking about DHT. Creams and gels produce dramatically higher DHT than injections. If you have any concern about pattern baldness or BPH, start with injections.

5. Going alone. TRT works best with a knowledgeable clinician who actually reads your labs and adjusts. The 'just bro-science it' approach causes more problems than it solves.

Every man on TRT benefits from systematic tracking of: dose timing, injection site rotation, energy / mood / libido / sleep ratings, weight, lab results over time, and side effects.

This is what MyTRT is built for. Free on iOS and Android. Pro adds AI lab extraction, unlimited history, and advanced trending. Whether you use our app or a notebook, the men who track tend to optimize faster and feel better than the men who don't.