Testosterone replacement therapy (TRT) is prescribed for men with confirmed low testosterone and symptoms, not as a general boost or anti-ageing treatment. When appropriate, it can improve libido, energy, mood, and muscle mass. However it is a real medical treatment with real risks.
Possible side effects include acne or oily skin, fluid retention, breast enlargement or tenderness, an increase in red blood cell count that can thicken the blood, and worsening of obstructive sleep apnoea. A key consequence men often do not realise is that TRT suppresses the body's own production and can significantly reduce sperm count and fertility, so it is generally avoided in men still hoping to have children. Its effect on the prostate and cardiovascular system requires monitoring.
TRT should only be started and supervised by a doctor with baseline and follow-up blood tests. Never source testosterone from gyms or the internet. Discuss benefits, risks, and your fertility plans with a clinician before considering it.