Originally Posted by
stillsleeping 
Most drugs trigger the reward centres of your brain.
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That's exactly 100% correct! THe drug triggers your brain reward center for so long that it goes into a primal fight or flight response when the reward is threatened! Addiction is a VERY powerful thing that makes it so incredibly difficult to stop.
Why would the brain want to stop and go into shock & pain for days or weeks when it can simply keep doing what it's been doing. I kid you not, the threat of taking the drug away is tantamount to threatening death and pain it's so strong. I'm not kidding either!
You have to realize too that drugs completely alter the brains chemistry! So much so that it turns people into completely different beings. Beings that want NOTHING more than to stay high!