Testosterone Replacement Therapy (TRT)

What Testosterone Replacement Therapy Is

Testosterone replacement therapy (TRT) is a medically supervised treatment that restores testosterone to a healthy physiologic range in men diagnosed with hypogonadism — a condition in which the testes do not produce enough testosterone, or the brain’s signaling to the testes is impaired. Testosterone is the primary male sex hormone, but its influence extends well beyond reproduction: it supports muscle mass, bone density, red blood cell production, mood, cognition, libido, and metabolic health.

TRT is not a single product. It is delivered through several forms, each with its own pharmacology: intramuscular or subcutaneous injections (testosterone cypionate or enanthate), transdermal gels and creams, long-acting pellets implanted under the skin, and in some cases nasal or oral preparations. The goal is consistent restoration of testosterone — not supraphysiologic dosing — under ongoing laboratory monitoring.

Understanding Testosterone Lab Values

A diagnosis of low testosterone is made with a morning blood test, ideally drawn between roughly 7 and 10 a.m. when levels peak, and confirmed on at least two separate occasions because testosterone fluctuates day to day. Reference ranges are assay-dependent and vary between laboratories, so values should always be interpreted against the specific lab’s stated range.

As a general guide, many laboratories report a total testosterone reference range of roughly 300–1,000 ng/dL for adult men. The Endocrine Society and the American Urological Association have historically used a threshold near 300 ng/dL total testosterone as a common cutoff below which, when paired with consistent symptoms, hypogonadism may be diagnosed. Because much of circulating testosterone is bound to sex hormone-binding globulin (SHBG), free testosterone is often measured as well, particularly when SHBG is high or low. A complete evaluation typically also includes luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to distinguish primary (testicular) from secondary (pituitary/hypothalamic) hypogonadism, along with estradiol, prolactin, and a complete blood count.

What the Numbers Mean

• Low LH/FSH with low testosterone suggests a secondary (central) cause involving the pituitary or hypothalamus.
• High LH/FSH with low testosterone points to a primary (testicular) cause.
• Symptoms matter as much as the number. A borderline value with clear symptoms is interpreted differently than the same value in an asymptomatic man.

Symptoms and Who Should Be Evaluated

Low testosterone produces a constellation of symptoms that overlap with many other conditions, which is why testing rather than assumption is essential. Common signs include:

• Reduced libido and erectile difficulty
• Persistent fatigue and low energy
• Loss of muscle mass and reduced strength despite training
• Increased body fat, particularly around the abdomen
• Depressed mood, irritability, or reduced motivation
• Difficulty concentrating or “brain fog”
• Decreased bone density over time

Men who should consider evaluation include those with these symptoms, men with conditions associated with low testosterone (type 2 diabetes, obesity, prior chemotherapy or pituitary disease), and men on long-term opioids or glucocorticoids. Importantly, TRT is generally not appropriate for men trying to conceive in the near term, because exogenous testosterone suppresses the body’s own sperm production. It also requires caution in men with untreated prostate cancer, severe untreated sleep apnea, uncontrolled heart failure, or an elevated red blood cell count.

What Optimization Looks Like

Well-managed TRT is a long-term, monitored relationship between patient and clinician — not a one-time prescription. After starting therapy, levels are rechecked to confirm testosterone has reached a stable mid-range target, and symptoms are reassessed over weeks to months. Ongoing monitoring typically includes periodic testosterone levels, hematocrit (because testosterone can raise red blood cell mass), estradiol when symptoms warrant, and PSA with prostate evaluation per age-appropriate guidelines.

Optimization is about more than a single lab number. It means resolving symptoms, protecting fertility when relevant (sometimes by pairing therapy with agents that preserve testicular function), avoiding supraphysiologic peaks, and addressing the lifestyle factors — sleep, body composition, alcohol, and metabolic health — that independently influence testosterone. A thoughtful program treats TRT as one component of broader longevity and preventive care rather than a standalone fix.

Getting Started Safely

Because symptoms are nonspecific and the diagnosis depends on properly timed, confirmed lab work, the right first step is a structured evaluation rather than self-treatment. A comprehensive assessment helps determine whether your symptoms reflect low testosterone, another hormonal imbalance, or a non-hormonal cause entirely.

Take the ENNU Life Health Assessment to begin your evaluation.

Educational only, not medical advice; consult a licensed clinician. Reference ranges are assay-dependent and individual results must be interpreted by a qualified medical provider in the context of your full history and examination.