I developed a stutter at 28 around the tail end of my battle with alcoholism. Idk if it was from the actual drinking, a head injury I didn’t realize I suffered (I blacked out a lot), or just the overwhelming amount of stress that comes with alcoholism. Doctors haven’t given me many answers either. I’ve read that heroin abuse can lead to stuttering, but haven’t learned of any other drugs causing an onset stammer. Kratom seems to make my stutter almost non-existent at least when I don’t take it regularly. Hope you’re able to find some solid answers, and info.