"Puberty blockers did not lead to mental health improvements, she said, most likely because the children were already doing well when the study began.
“They’re in really good shape when they come in, and they’re in really good shape after two years,” said Dr. Olson-Kennedy, who runs the country’s largest youth gender clinic at the Children’s Hospital of Los Angeles."
You get a null effect for psychological treatment if the group you are treating is, psychologically speaking, already equal to the control.