The complete guide to TRT for men over 35

From around the age of 35, most men begin to notice something shifting. The energy that used to be there in the morning takes longer to arrive. The focus that once came easily starts to feel effortful. The drive, the motivation, the sense of being fully present in your own life, it all becomes a little quieter, a little harder to access.

Most men attribute this to getting older and get on with it.

The evidence suggests they should not.

Testosterone levels in men decline at approximately 1% per year from their early thirties.

That figure sounds small in isolation. Compounded across a decade it represents a significant hormonal shift, one that can affect energy, mood, cognitive function, libido, body composition, and sleep quality in ways that are clinically meaningful but frequently dismissed, both by healthcare providers and by the men experiencing them.

A 2024 cross-sectional survey of 973 UK men found that 49% showed likely testosterone deficiency based on validated clinical symptom scoring, yet only 5% had ever received a formal diagnosis. The gap between those two numbers is where most men are quietly living, assuming what they are feeling is simply the cost of ageing.

It is not.

What testosterone actually does

Testosterone is the primary male sex hormone, produced mainly in the testes and regulated by the brain’s hypothalamic-pituitary axis. It governs a significantly broader range of physiological functions than most men realise.

Energy metabolism. Mood regulation. Cognitive function, particularly focus, working memory, and mental sharpness. Libido and sexual function. Muscle mass and the body’s ability to maintain lean tissue. Bone density. Sleep architecture. Red blood cell production. The ease with which fat is stored and lost.

When testosterone is at optimal levels, most men never think about it. When it declines, the effects are diffuse enough that they are easy to attribute to other causes, such as stress, poor sleep, age, or a demanding life. This is precisely why testosterone deficiency is so frequently missed.

The problem with how testosterone is currently assessed

If you have ever had your testosterone levels tested by a GP and been told your results are normal, it is worth understanding what normal means in this context.

The NHS reference range for testosterone is 8.6 to 29 nmol/L. This is an extraordinarily wide range, so wide that a man presenting at 9 nmol/L with clear, significant symptoms can be told he is normal and sent home.

Clinical experts, including those working within the British Society for Sexual Medicine, increasingly advocate for a functional threshold closer to 15 nmol/L as the appropriate benchmark for optimal health in men. The NHS range was constructed to capture population data, not to define what level of testosterone a specific individual needs to feel and function at their best. These are different questions, and the NHS range does not answer the second one.

This is not a criticism of GPs, who are working within the parameters of a system not designed for this kind of nuanced hormonal assessment. It is simply an explanation of why a man can be told he is fine and not feel fine at all.

What low testosterone feels like

The clinical picture of testosterone deficiency is rarely dramatic. It tends to arrive gradually, over months or years, in ways that are easy to normalise.

Persistent fatigue that sleep does not resolve. A reduction in motivation and drive that is difficult to explain to others. Increased difficulty concentrating. A quietening of libido that affects confidence and relationships. Changes in body composition, including more difficulty maintaining muscle and more tendency to carry fat around the abdomen. Low mood, a flatness that is not quite depression but is not wellness either. Disrupted sleep. In some men, increased irritability or emotional sensitivity.

None of these symptoms are specific to low testosterone. They can have other causes, and your clinician will assess the full picture. But for many men, the combination of several of these symptoms, confirmed by blood testing showing suboptimal testosterone levels, points clearly to a hormonal explanation that is both identifiable and treatable.

What TRT is and what it is not

Testosterone Replacement Therapy is a clinically established treatment that restores testosterone to physiologically appropriate levels in men whose natural production has declined.

It is not a performance drug. It is not steroids in the sense that word is used colloquially. The doses used in TRT are calibrated to restore normal physiological levels, not to exceed them. It is a medical intervention for a medical condition.

At NUPHASE, every TRT protocol begins with a Randox blood panel. The panel measures your actual testosterone levels, along with the other markers your clinician needs to assess your hormonal profile fully. Your clinician then reviews your results, speaks with you about your symptoms and history, and, where treatment is clinically appropriate, recommends a prescription compounded to your specific levels.

The compounding element matters. Most standard TRT prescriptions come in fixed doses. A compounded prescription is made specifically for you, at the concentration your blood results indicate, which means your treatment can be calibrated with a precision that off-the-shelf formats cannot offer.

What ongoing TRT involves

TRT is not a one-time prescription. Hormone levels change as the body responds to treatment, and ongoing monitoring is essential to ensure your protocol continues to be appropriate and effective.

At NUPHASE, monitoring is built into your subscription. Your clinician reviews your progress at regular intervals, checks your levels through repeat blood testing, and adjusts your prescription as needed. The goal is not simply to get your testosterone into a range and leave it there. It is to find the level at which you feel and function at your best, and to maintain it over time.

The bottom line

If you recognise the symptoms described in this article, the most important thing you can do is get your levels tested. Not a standard panel with a binary normal or abnormal result, but a comprehensive blood test assessed by a clinician who understands what the numbers actually mean in the context of how you are feeling.

The tiredness, the low mood, the loss of drive. These are not inevitable. They are signals worth investigating.

Frequently asked questions