This story is very predictable.. and the delivery of it is silly..
This weak nerdy guy injects himself with a substance to help him become more of a "Man" but activating his "dormant Primitive" genes. Making him into a powerful raging "Caveman".
It's got similar aspects of the "Incredible Hulk" story line.
Eventually , these injections and changes back fire and he goes crazy, finding himself losing control in fits of rage.
The thing that turns me off most about this, is not the story itself, just the really bad delivery of it. It seemed very thrown together without a lot of thought.