TRT

TRT stands for testosterone replacement therapy, an approved medical treatment category rather than a single research compound. It refers to injectable forms of testosterone, most often testosterone cypionate or enanthate, prescribed under medical supervision to men diagnosed with hypogonadism, a condition where the body does not produce enough testosterone on its own. This entry lays out the published research on those medicines so researchers can compare hormone pharmacology side by side; it does not guide anyone's actual use of them.

What it is

Testosterone cypionate and enanthate are both esters, meaning testosterone is chemically attached to a fatty-acid-like tail that slows its release after it is dissolved in an oil solution and injected into muscle or under the skin. That slow release is what allows injections to be spaced roughly a week or two apart while keeping blood testosterone levels relatively steady, rather than requiring the unmodified hormone to be given every day.

As a treatment category, TRT is reserved in most health systems for men with a documented diagnosis of hypogonadism, confirmed through repeated blood testing showing low testosterone alongside recognized symptoms such as fatigue, low sex drive, or loss of muscle mass. It is not the same thing as testosterone use for general performance or body composition goals outside of a diagnosed medical condition, a distinction the research literature and prescribing guidelines both draw clearly.

How it is studied

The modern research record on TRT includes several large, randomized, placebo-controlled human trials, the most significant of which specifically tested cardiovascular safety in men with existing heart disease risk, and a separate coordinated set of trials examining physical function, sexual function, and quality of life in older men with confirmed low testosterone. That trial evidence sits alongside decades of smaller studies and clinical experience with these two testosterone esters as prescription medicines.

What studies report

A large randomized trial in more than 5,000 men with hypogonadism and existing or elevated cardiovascular risk found that testosterone therapy was not worse than placebo for the combined rate of heart attack, stroke, and cardiovascular death when used as prescribed. [1]
A coordinated set of trials in several hundred older men with confirmed low testosterone found that testosterone gel improved sexual activity, sexual desire, and erectile function compared with placebo over one year, while walking distance improved only when data from all of the trials were combined. [2]
A systematic review and meta-analysis of randomized trials found that testosterone therapy given by injection into muscle increased fat-free mass by about 5.7 percent and body strength by 10 to 13 percent, three to five times the size of the changes seen with testosterone applied to the skin. [3]

What is not known

The main cardiovascular safety trial also found a higher rate of a heart-rhythm problem called atrial fibrillation in the testosterone group, an unresolved signal that researchers are still working to explain. TRT's research record is concentrated in diagnosed hypogonadism rather than in wider populations, so how the same medicines behave in men without a confirmed deficiency is not addressed by this evidence.

Reported adverse findings

In the large cardiovascular safety trial, men receiving testosterone had a higher rate of nonfatal irregular heart rhythms, including atrial fibrillation, than men receiving placebo. [1]

Regulatory status

Testosterone cypionate and enanthate are approved prescription medicines in the United States and Canada for diagnosed male hypogonadism, and carry a boxed safety warning noting that heart attack and stroke may occur more often as a result. They are not approved for use in women, in men without a diagnosed deficiency, or for general performance or bodybuilding purposes.