system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 how drugs like bath salts and amphetamines give people “super human strength”
gpt
So with the group of drugs known as bath salts we're dealing with chemicals known as synthetic cathinones. Most varieties of bath salts contain either mephedrone or methylenedioxypyrovalerone, which are chemically similar to (but much more powerful than) khat, an organic stimulant found in the Middle East and East African countries.  


The main issue with bath salts is that the user has no way of knowing what chemicals were added to the mix, and no way of knowing what a "proper" dosage is. They just get this package of stuff, usually in crystal form, and it's really a crapshoot as far as how severely what you take will affect you.   


These chemicals are able to cross the blood-brain barrier, which means they can completely alter your normal neurochemical functions and impact mood, thought, perception and behavior in really alarming ways. Sometimes they can tap right into your lizard brain, the primitive part of the brain that controls things like the fight-or-flight response. They can also prevent you from sleeping, they can cause severe overheating, and all of that combined can result in what appears to be mindless rage, or intense paranoia, or horrible paranoid delusions.   


So when someone's under the effect of all these nasty chemicals, their muscles aren't literally getting bigger, and they haven't lost the ability to perceive pain, it's just that the primitive parts of the brain are absolutely freaking out, like you're suddenly in the most horrific, panic-inducing survival situation you could possibly imagine. It's like suddenly you're a big, human-shaped crocodile that's fighting for its life, and when your brain and body are in that state, normal rational thought just isn't happening.