Look for effect of testosterone on Tourette’s syndrome. It’s a neurological disorder that is closely related with stuttering. The researchers discovered that injecting patients with T made their symptoms severe but giving them anti-androgens alleviated their involuntary movements. I even found a professor at USC that investigated the effect of anti-androgen drugs that suppress T production in stuttering patients back in 1998 and he saw positive results. However, he says in his paper that the adverse effect of low T doesn’t justify this remedy for stuttering which honestly makes sense. Just see the ratio of female to male stutters as another evidence.