There is lots of other evidence. My nephew took puberty blockers for precocious puberty. He grew up to be a healthy adult male.
I'm going to give the same lecture I've given five or six times in this discussion before.
First, precocious puberty is not the same as dysphoria. Using outcomes from precocious puberty as justification for dysphoria is like using outcomes for cancer treatment as justification for doing chemotherapy for warts.
First, some basics. Puberty is predominantly a two-part process. It involves two major functions, the pituitary and the adrenal. The adrenal gland triggers repeatedly throughout childhood development, as it drives bone growth. The pituitary normally triggers at the onset of puberty, and continues to serve a role in hormonal regulation after puberty has completed. During puberty, the adrenal triggers rapid growth of the long bones (which results in increased height), as well as growth of fine underarm hair and fine pubic hair. When puberty has completed, the adrenal gland triggers closure of the growth plates, which stops the long bones from growing longer. The pituitary triggers hormonal production by the gonads, as well as several physical changes that differ by sex. In males, it leads to facial and body hair growth, thickening of the jaw and brow ridges, thickening of the adam's apple which causes lowering of the voice, lengthening and thickening of the penis, and descent of the scrotal sac away from the body to support higher volume sperm production. In females, it leads to widening of the hips, maturation of lactation glands in the breast region, enlargement of the uterus, and menarche. In both males and females, the adrenal causes armpit, pubic, and leg hair to coarsen and rapid accretion of bone density. When the adrenal has completed it's process, it signals the pituitary to STOP driving pubertal changes, and to switch over to either constant production of testosterone in males, or cyclical production of estrogen, progesterone, follicle-stimulating hormone, and luteinizing hormone in females.
In precocious puberty, the pituitary process begins before the adrenal process, causing them to be out of sync. In addition to the sex-related changes, this also means that short bones start acreting density when they are not expanding in length. This can cause pain as well as risks warping of the bones and later disability. If left untreated it can result in damage to the bones and surrounding tissue when the bones try to lengthen after hardening. Using blockers in precocious puberty halts the production of hormones that trigger those changes for a while, to allow the adrenal function to trigger and fall into alignment with the pituitary.
In someone with dysphoria those two processes are not out of alignment at all. Using blockers forces them out of alignment. If used for a very short time - on the order of just a few months - the risk is probably pretty low. A few months delay in the pubertal process is well within the window of normal adolescent development. If used for much longer than that, however, certain steps in the process can be missed entirely. For example... if blockers are in place when the child would normally be accreting bone density, and the adrenal signals the growth plates to close, those bones cannot accrete enough density to maintain the strength they need as an adult. They can leave the individual with permanent osteoporosis. If bockers are in place when the penis would normally lengthen and the scrotal sac drop, it can result in the individual being left with a permanently child-sized penis and unable to achieve orgasm, as well as a high likelihood of sterility because the testes didn't properly mature. This happened to Jazz Jenkins, and it's been acknowledged as a risk for males. In females, it can result in the uterus never enlarging, which can make childbirth very high risk or even impossible.
All of this is only a discussion of the physical changes that occur as a result of the pituitary-adrenal partnership. It doesn't discuss the cognitive changes that occur during puberty at all. I know far less about that, but I do know that a lot happens. My goddaughter's endocrinologist gave an overview of some of it, things like the development of a tendency toward romantic boding in addition to friendship bonding.
