What is TRT (testosterone replacement therapy)?

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TRT is a medical treatment in which a doctor gives testosterone to a man whose body cannot make enough of it, to bring his level back to normal.

What is TRT (testosterone replacement therapy)?
The term you hear in clinic ads and at the gym
You may hear the word 'TRT' in ads for men's hormone clinics or in gym conversations. It is easy to confuse it with steroids, or to be unsure who actually gets it. So what exactly is TRT?
In short
A treatment that tops up missing testosterone
TRT is a treatment in which a doctor gives testosterone as a medicine to a man whose body cannot make enough of it. The letters stand for Testosterone Replacement Therapy. 'Replacement' means the medicine stands in for the part the body cannot make.
What is testosterone?
The main male hormone, made in the testicles
A hormone is a substance made in one part of the body that travels in the blood and carries a signal to another part. Testosterone is the main male hormone, and men make it mostly in the testicles. It helps muscles and bones grow, and keeps up male body features and sex drive.
What is testosterone deficiency?
It comes from a problem in the testicles or the brain
When the testicles make little or no testosterone, this is called 'testosterone deficiency'. The cause lies in one of two places: the testicles themselves, or the part of the brain that sends the 'make it' signal to the testicles. Stopping anabolic steroids (muscle-building drugs modeled on testosterone) after using them is one of the brain-side causes.
When testosterone is low
Less sex drive, weaker bones, less energy
Men with low testosterone have less sex drive, trouble getting an erection, and difficulty having children. They can also get 'osteoporosis', where bones become weak and break easily, and feel weak and low on energy. Testosterone does fall with age, but not as sharply as a woman's hormones fall at menopause.
How is it diagnosed?
Symptoms plus low levels measured twice
A doctor diagnoses testosterone deficiency when a man has the symptoms of low testosterone and his blood test level is also clearly low. The level is checked with a morning blood test, repeated on another day. Symptoms alone, or a single low reading, are not enough for the diagnosis.
Forms and goal
Back to the middle of the normal range
Testosterone medicines used for TRT come in several forms, such as a gel rubbed on the skin, a patch, and injections. The goal of treatment is to bring the testosterone level back into the normal range for healthy men, around the middle of that range. During treatment, blood tests are used to check the level.
How it differs from steroid misuse
Same hormone, different purpose and amount
Using testosterone without a prescription to build muscle is 'misuse', meaning a drug is used wrongly or too much. In misuse, people take far larger amounts than those used in treatment. TRT only adds back what is missing to return to the normal range, so its purpose and amount are different.
What about the heart?
In a large trial, heart attacks and strokes did not increase
In a large trial, middle-aged and older men with low testosterone and a high risk of heart disease used testosterone gel or a fake gel. Heart attacks, strokes and heart-related deaths showed no difference between the groups. A heart attack is when a blood vessel feeding the heart muscle gets blocked. However, 'atrial fibrillation', where the heart quivers irregularly, and blood clots blocking lung vessels were more common with testosterone.
The blood gets thicker
The share of red blood cells goes up
Red blood cells are the red cells in blood that carry oxygen around the body. Testosterone treatment raises the share of the blood made up of red blood cells, which makes the blood thicker. So doctors check this share with blood tests before starting treatment and during treatment.
Common misconception
Does adding testosterone make it easier to have children?
It is the other way around. When testosterone comes from outside, the brain cuts the 'make it' signal it sends to the testicles, so testosterone inside the testicles and sperm production both fall. In a male birth control trial, among healthy men who kept getting testosterone injections, about two out of three had no sperm at all within half a year. So treatment guidelines say not to start TRT in men who plan to have children soon.
Summary
A medical treatment for a testosterone shortage
TRT is a treatment in which a doctor tops up testosterone to the normal range in a man whose body cannot make enough. Adding testosterone does not make it easier to have children; it actually lowers sperm. Related terms: testosterone, anabolic steroids, red blood cells.