ID This 80s Novel?

I remember reading a book review in Playboy back in the late 80s or early 90s, and never getting around to reading the book. Here’s what I remember about it: The protagonist was a disgraced doctor who had lost his license and done some prison time for selling drugs. Later in life, he’s in a rural community where people suddenly start exhibiting hypersexual or narcissistic behavior, and he discovers that the town fathers are dosing the water system with lithium. Ring any bells?

Sodium rather than lithium, but it sounds like it has to be The Thanatos Syndrome by Walker Percy.

Sure looks like it, thanks!