So I had this movie as the second feature on a blu-ray with The Beast of Hollow Mountain.

So a scientist creates a serum that can regress evolution. He tries it on a cat which turns it into a sabretooth tiger and eventually on himself.

Standard fare for 50's movies. When people mention the term B-Movie this is the sort of thing that comes to mind for me. It's not much good but I didn't mind watching it for the sake of curiosity.