I saw this movie on television some time in the mid 80’s.
The details are kind of hazy in my memory, but I remember there was a swamp creature. There was a drug that, when given to somebody, made him more like he was already. If it was given to somebody who was kind, he would become more kind, and if he was evil, he would become more evil.
Swamp Thing?
Was thinking Swamp Thing ( 1982) or maybe Legend of Bogey Creek (1972)