A drug that causes the user to travel to another world.

Oct 31, 2023
Probably published between 1960 and 1978. The hero is testing a drug that causes its users to hallucinate about the same world. If they overdose on the drug they physically transfer to the world. As far as I remember it's a pre industrial world. The hero possibly joins a traveling fair. He builds himself a guitar, an unknown instrument in this world.
This sounds like a very Phillip K Dick-type idea, although it's been a long while since I read any of his books. Did these details crop up in The Three Stigmata of Palmer Eldritch?