In my experience it goes like this:
You first try meth and are absolutely amazed at how good it feels. You have no chemical dependance, but why wouldn't you try something that makes you feel this good again, just occasionally.
You integrate it it into your life and soon your body learns that nothing gives you more dopamine than this lovely chemical. Over some period of time that depends entirely on how often you use, the incredibly good feelings don't happen unless you up the dose and increase your body's dependence and tolerance.
Continued use over time causes down-regulation of the dopamine receptors in your brain (it repairs less and less of the damaged receptors) and then eventually, due to the increased doses and/or frequency of your use, it no longer feels as good and depletes most of your available dopamine with each use. Your brain now convinces you that you need meth, not because you need to feel good, but because your dopamine levels are depleted and meth is the easiest and fastest way to restore the balance.
It's a subtle shift over time but now you're addicted.
You are most susceptible to continued use if you use frequently, but if you allow your dopamine receptors to recover periodically, your brain will crave it less as your dopamine levels recover and you are better able to use your willpower to restrain your use. You'll never stop craving it because the memory of those incredible first few times will never fade, but you can beat it. Though it will always be like the most incredible lover you ever met slipped away.....
