If you're taking dextroamphetamine, you're not doing meth or anything even close, pharmacologically related yes, but nothing even in the same category IMO. Meth is quite a dirty drug indeed, IMO. Though, I'm sure many people here would be more than willing to disagree with me. Dextroamphetamine is an ingredient of adderall/ADHD meds, not meth. It is pharmacologically related to meth, but it's a bit more "user friendly" so to speak as it's a very common prescription drug. Obviously, this doesn't mean it is free of side effects. It's addictive as well (though not as badly as meth), and for some people, it is extremely addictive. Theoretically, if you took enough of it, the drug could have similar side effects as meth but not unless you were doing a very large amount of it.
Meth is actually prescribed for a few people, in very controlled dosages. However, if you are doing meth that you purchase illegally, there's the risk of adulteration which is commonplace with it. I hate to recommend one drug over another because as you'd expect not using stimulants is better for your body than using them (unless it's your own script), but if you're using stimulants in order to enhance performance or any other reason that would cause a logical minded person to be drawn to them, you'd be way better off sticking with prescription stimulants of some kind rather than taking meth. At least, you'd know what you're getting and while it's addictive and has side effects that can be nasty, it's nowhere near as bad as meth is.
I used to take adderall sometimes before I had a script for it myself, but there's no way I'd ever touch meth with a 10 foot pole personally. Way too much potential for things to go wrong from what I heard. I've known a few people who did meth, and the story never ended well unfortunately. People get addicted without realizing it, and it can have serious side effects including loss of teeth and everything else you've heard about it. Meth is a drug to stay away from IMO.
Also, getting your stuff from a source that originates from North Korea doesn't sound like the greatest idea. I've never heard of anyone doing that, so I can't really say from firsthand experience obviously but it sounds like a really bad idea. Hell, being a hardcore methead is probably less dangerous than getting drugs that from NORTH KOREA. To be honest, I kinda wonder if you just made that part up, at least I hope you did..... for your sake. I've heard of stuff coming from Mexico and a lot of other countries and have smoked plenty of schwag myself over the years that came from all sorts of other countries and obviously took/smoked tons of stuff where I didn't know where it came from and never really cared either, but wouldn't even consider anything that I was aware of as having come from North Korea. Especially when IME there's plenty of drugs of all types around that aren't "North Korean" as you said.
If you do use meth despite the risks, I would strongly advise that you limit your usage to a very occasional basis. It is highly addictive. As or more addictive than opiates, and it's a nasty addiction. Perhaps, even nastier than heroin many have said who used it regularly or had family members who did. If you use it regularly, you can actually get psychosis if you don't sleep well. And if you're doing it, always make sure that you sleep and take good care of yourself (especially dental care). People do lose their teeth from meth and it's not an urban legend but taking good care of yourself would likely reduce the chances of this happening. Though, I wouldn't want to chance it personally. Keep your use of it very occasional or better yet don't use it. But yes, it is true that stimulants can increase memory and other aspects of performance in anyone, but meth not generally as much due to its extreme potency and the possibility of adulteration. The negative effects of meth vastly outweigh the positive for nearly everyone who uses it as far as I know.