system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Meth. Why is it so horrible and what does it do to people?

I have no experience with meth but I see it referenced often. Shows I watch portray meth in vastly different ways. 

What's the true nature of meth ?

I'm never going to try it, just curious.
gpt
It's so horrible because suddenly nothing else is of value anymore. You choose it over everything. It's always on your mind. 

It does a variety of things to people. Being a stimulant it keep a you awake and suppresses appetite for around 24hrs. People often binge it so that this happens for days on end. They hallucinate and become paranoid, anxious because of sleep deprivation. They become incredibly thin and frail. Your cardiovascular system is under stress for a very long time, you overheat, you dehydrate, you forget general hygiene, your mouth begins to go red and sore. 

Psychologically, it plays on your reward system, dopamine. This is where the addiction sets, as dopamine is released when we do basic survival stuff, eating, sex, etc. Soon enough the brain associates meth with this same survival reflex.