PCP inhibits those neural pathways that limit your use of strength for your own safety =D In the Seals, they say that you are capable of 10x more than your brain allows you -- and they train you to unleash that.
With PCP, you unleash it right away -- unfortunately, the human body isn't really set up for that and users tend to injure themselves. Of course, many of the stories of PCP users are grossly exaggerated. Some of them, however, are true, which is scary enough.