As you age, you may notice a gradual loss of strength, stamina, and lean muscle. This change isn’t just about time in the gym – it’s often linked to declining testosterone levels. Building muscle, recovering from workouts, and staying motivated become harder if you’re experiencing low testosterone.
Testosterone Replacement Therapy (TRT) offers a medical solution for men with low testosterone and may help them rebuild and maintain muscle mass safely and effectively. In this article, we’ll explain how TRT can support muscle gain, how long it takes to work, and what you need to know about accessing testosterone therapy in the UK.
What is Testosterone Replacement Therapy (TRT)?
TRT is a form of hormone replacement therapy used to restore normal testosterone levels in men whose natural production has declined due to age, illness, or other causes.
Common TRT methods include:
- Testosterone injections
- Gels, patches, or capsules
- Testosterone with a fertility add on can be used if clinically appropriate to stimulate natural testosterone production
Find out more about how to get TRT in the UK in our guide.
Testosterone, TRT, and muscles
Healthy testosterone levels are important for building and maintaining muscle, and TRT can help restore these benefits if your levels are low.
Testosterone supports muscle growth by increasing protein production in your muscle cells – the process your body uses to repair and build stronger muscle tissue. It also helps reduce muscle breakdown, making it easier to hold onto muscle even when you’re on a low-calorie diet.
Optimal testosterone levels can improve your energy, motivation, and workout performance, helping you get the most out of your workouts. It also supports fat loss, which can make your muscles look more defined.
TRT and muscle gain: What the research says
Clinical research supports the link between TRT and muscle gain:
- Men who trained while receiving testosterone replacement therapy gained lean muscle mass [1].
- In men with low testosterone, research showed that testosterone patches resulted in favourable changes in body composition. Muscle strength improvements for both the control group and the group taking testosterone at 12 months compared with baseline scores. Strength increased 38% (p =.017) in the testosterone group and 27% in the control group (p =.06). However, it is unclear if this was down to the testosterone, or the vitamin D each group received [2].
TRT can help your muscles respond more effectively to exercise, allowing you to build strength that low testosterone might have made difficult before.
Low testosterone and muscle loss
Low testosterone, or hypogonadism, can lead to noticeable physical and mental changes. Common low testosterone symptoms include:
- Decreased muscle mass and strength
- Increased body fat
- Fatigue and low motivation
- Mood changes and low confidence
- Decreased libido
Read our guide to the symptoms of low testosterone for more details.
Normal testosterone levels in men are between 8.7 and 29 nmol/L, but if it drops below 12 nmol/L, especially if you’re experiencing symptoms, you could benefit from TRT [3].
Testosterone injections
Testosterone therapy can be administered by injections, gels, patches, or capsules - your consultant will recommend the best method depending on what best suits your lifestyle. To stimulate the production of natural testosterone, hCG may also be used.
However, whilst receiving TRT, regular blood tests are essential to keep testosterone levels within the normal range, ensuring you stay safe and avoid excess or deficiency.
HCG for men on TRT
HCG may be added to a TRT plan when maintaining fertility and natural hormone production are priorities. It works similarly to luteinising hormones (LH), sending signals to the testes to continue producing testosterone and supporting healthy sperm development.
Some potential benefits of hCG for men include:
- Preventing testicular shrinkage
- Supporting sperm production
- Helping to stabilise mood and energy levels
This makes hCG a valuable option for men seeking both muscle support and long-term hormonal balance.
TRT, muscle gain, and steroid use
Anabolic androgenic steroids (AASs) are a prescription medicine used for conditions related to low testosterone [4]. However, it’s not unusual for men struggling to gain muscle or noticing a decline in strength to consider them a quick fix.
Without medical supervision, buying steroids and self-dosing can result in several detrimental physical and psychological effects, including heart and liver problems, high blood pressure, and paranoia.
For men with low testosterone, TRT can offer a clinically backed route to supporting strength without the risks associated with steroid misuse.
For information, see our guide to TRT and steroids.
How long does testosterone take to work?
The initial benefits of testosterone therapy usually appear within three to six weeks if accompanied by a training regime.
Typical timeline of the physical effects of TRT, when accompanied by training regime:
- Weeks 1 to 6: Energy, motivation, and mood may begin to improve.
- Weeks 6 to 12: Continued improvements in motivation, energy, and physical drive. You may notice changes in muscle strength, wellbeing, and confidence.
- Months 3 to 6: Lean muscle mass may increase, fat around the waist may decrease, improvements in strength and red blood cell production.
- Months 6 to 12: Further fat loss and reduction of waist circumference
- Months 12+: Measurable improvements in bone density and stabilisation of psychological wellbeing
For a more detailed timeline, read our full guide:How long does TRT take to work?
How to maximise TRT muscle gains
Your day-to-day habits will make a big difference to how fast and effectively you rebuild muscle while on TRT. Strength training is key, and sticking to a routine that gradually increases weight, reps, or difficulty will help your body respond and grow stronger. Eating enough protein and healthy fats, and staying hydrated, also supports recovery, repair, and overall hormone balance.
Managing stress and limiting alcohol will further enhance your progress.
Who shouldn’t use TRT?
TRT isn’t suitable for everyone. Your medical specialist will use blood tests and consultations to assess your suitability before prescribing TRT. However, generally, if you have untreated prostate cancer, certain heart conditions, or uncontrolled sleep apnoea you may need to consider alternative treatments.
If you’ve been struggling with energy, motivation, or building strength, and your testosterone levels are low, testosterone therapy may offer the solution.
References
- Bhasin, S. et al. (1996) Testosterone increases muscle mass by inducing hypertrophy, The Journal of Clinical Endocrinology & Metabolism, 81(5), pp. 1575–1581.
- Kenny, A.M., Prestwood, K.M., Gruman, C.A. (2010) Effects of transdermal testosterone on bone and muscle in older men, Journal of Gerontology, 55(5), pp. M220–M225.
- Smith, J. (2024) What is a normal testosterone level for your age? [online]. Medichecks. (Accessed 12 November 2025).
- NHS, (2022), Anabolic Steroid Misuse[online] (Accessed 25 November 2025).
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