Testosterone Replacement Therapy (TRT) involves administering testosterone to treat symptoms of low natural levels. The effect of this therapy on an individual’s height depends entirely on their biological age and whether the specialized growth centers in their bones are still active. For individuals whose skeletons are still maturing, the introduction of testosterone can significantly affect their final adult height.
How Human Height is Determined
Linear growth occurs at specific cartilaginous areas called epiphyseal plates, or growth plates. These plates are located at the ends of long bones, such as the femur and tibia. Throughout childhood and adolescence, specialized cells within these plates create new cartilage, which is then converted into new bone tissue. This continuous process causes the individual to grow taller.
This growth process is regulated by a network of hormones. Growth Hormone (GH) stimulates the liver to produce Insulin-like Growth Factor 1 (IGF-1), which promotes the growth of cartilage cells. Sex hormones, primarily testosterone and estrogen, play a dual role during puberty. They initially trigger the rapid growth spurt characteristic of adolescence.
However, the sustained presence of sex hormones eventually signals the end of the growth process. Estrogen, which is produced when testosterone is converted in the body, is the primary hormone responsible for triggering the final closure and fusion of the growth plates. Once this fusion, or “epiphyseal closure,” is complete, the cartilage is replaced by solid bone, and no further increase in height is physically possible.
Testosterone and Premature Growth Plate Closure
The timing of growth plate fusion is crucial, and introducing external testosterone during the growth phase can shorten the window for growth. When high doses of testosterone, such as those found in some forms of TRT or anabolic steroid use, are administered to a child or adolescent, the body experiences an accelerated hormonal environment. This rapid increase in circulating testosterone is quickly converted into estrogen in peripheral tissues, including the growth plates.
This flood of estrogen acts as a premature signal, causing the growth plates to mature and fuse much earlier than they would naturally. The individual experiences an early and rapid growth spurt, but this is immediately followed by the cessation of all linear growth. The net result of this premature fusion is a final adult height that is shorter than the individual’s genetic potential. The younger the child is when the therapy begins, the greater the risk of compromising their final mature height.
Why Adult TRT Does Not Affect Height
For the typical patient seeking TRT, who is a skeletally mature adult, the therapy cannot influence height. The physical structure required for height gain, the epiphyseal plate, is no longer present in adults. The process of growth plate fusion is generally complete by the late teens or early twenties, leaving a fixed line of bone where the cartilage once was.
Once this fusion has occurred, the long bones are ossified and cannot be lengthened by any hormone. Therefore, administering testosterone to an adult will not cause them to grow taller, as the mechanism for linear bone growth has been permanently shut down. The therapy will instead focus on addressing symptoms of low testosterone, such as changes in body composition, energy levels, and sexual function.
Therapeutic Use in Delayed Puberty
There is a specific, medically supervised application of testosterone therapy for adolescents experiencing Constitutional Delay of Growth and Puberty (CDGP). These patients have significantly delayed puberty and bone maturation, which can lead to psychosocial distress. In these cases, a short course of very low-dose testosterone is sometimes prescribed to initiate the pubertal process.
The goal of this controlled regimen is to trigger the pubertal growth spurt without causing excessive bone age advancement. Clinicians carefully monitor the patient’s bone age using X-rays to ensure the growth plates do not fuse too quickly. This brief, low-dose treatment can improve the height velocity in the short term, helping the adolescent catch up to their peers, without compromising their predicted final adult height.