Getting to the root psychological causes and dealing with those has had the most positive impact on my speech and mental health. Most speech therapy was unfortunately useless for me, but psychological therapies were more helpful. Psychedelics might help overall mental health if you're careful and sensible about it, as I found, but probably won't directly improve speech. Someone mentioned Lee Lovett's book, which does have some useful tips, as well as daft ones. Find what works for you.