I will debunk the major ones now.
It causes acne or seeps through your skin as crystals!
This is the common myth, as you frequently see methamphetamine straw-men users with lots of acne on their faces. The truth is that it does make you perspire more, as well as be able to sit longer without moving or cleaning, but it at the same time makes you far more concerned with cleanliness, especially with sleep deprivation, as your senses are much heightened on it. Anyway, these problems have nothing to do with methamphetamine, anymore then playing football, having excess fat cells, being in a hot climate, or skating causes acne (or anything that makes you sweat more). Still, this problem is easily solved with a proper cleanser + toner + moisturizer regiment.
As for it seeping out of your pores as crystals, this is equally ridiculous. When you smoke it, the smoke CANNOT re-crystallize, period! Only the liquid can, perhaps where this myth came from, as one might have observed the bubbling liquid re-crystallize and thought their lunges as that. But once it gets to your lunges it is then processed like oxygen or nicotine smoke, and quickly enters the blood, it never enters the sweat glands.
It causes your teeth to fall out!
Meth mouth as it is called does not exist. You can brush your teeth after smoking to rid yourself of any chemical residue, but there really is none. Unlike say tobacco or cannabis, when you light it, it does burn and therefore smoke, it liquifies into vapour smoke, which is why it does not leave an odor, like an e-cig, so this would therefore have no real chemical trace on your teeth. Likely, if meth users are missing teeth, it is from lack of hygiene and a poor diet, which people have regardless of drug use.
It causes heart attack, strokes, or some other major health problem!
There is no evidence of this. All evidence is causal and there has never been any extensive testing to verify these claims. Methamphetamine users have the same life expectancy as anyone else, same rates of heart disease, strokes, etc, and also the concept of taking meth and then dying of a heart attack is completely ridiculous. These sensations are actually called panic attacks, which it can trigger if the user is not in a good mental state, but it has nothing to do with the drug. You cannot even get poisoned from it easily, not without taking an absurd amount. People with tolerance can take an insane amount of methamphetamine and live, those who die of heart attacks, strokes, etc, had some health problem and it just pushed them over the edge, or they went crazy with the excess energy it seems to provide (but it does not really, hence the crash, just delays the pain till later) and died from exhaustion.
It is super addicting!
It causes no physical withdrawals at ever, regardless of how long it was used. The only addiction is psychological, and no different to a gambling addiction. HOWEVER, heavy user of this in the long-term does lead to the damaging of dopamine and serotonin receptors, which take months to fully heal, even up to a year or multiple years if someone had done it for decades, perhaps. So the addiction is more there is no pleasure in life, cannot focus, do not think correctly, etc, hence relapse, but if the user can switch to other drugs, they can restore their neurochemistry with time, but waiting long enough for it to happen is rare, I agree, hence the addiction.
It is usually cut with all kinds of dangerous chemicals!
Meth is actually so cheap to create, that to cut it with even things like caffeine or anti-depressants would make it more expensive to produce, plus, as most users do tend to smoke it, if it is cut with anything it will not liquify correctly and leave dirty residue in the pipe, hence you cannot subtetly cut it and have people not notice. It is feasible to do it when it is just powder, but again, like the rule of street drugs in general, people who rip people off eventually get karma returned to them, the dealers who make actually serious profit, seriously do sell just a pure product, as they do not want to harm their customers and want them to return, plus, if they do cut it with anything, it is to enhance it, not to harm the end user, these are just old wives tales.
It makes you crazy and violent!
Too much of any stimulant and sleep deprivation will make anyone hallucinate or go delusional, but it never makes you permanently crazy, all you need to do is get some sleep and rest it off, plus there are anti-psychotics if it gets too hard to deal with. As for violence, there is no evidence to prove this, however, someone who is already violent may actually commit acts of violence, because methamphetamine gives the user tremendous confidence and physical re-distrubution of energy + prowess.
Only such-and-such demographic uses meth!
It is often thought of as a, excuse the slur, redneck, drug, and less commonly as the gay or transgender drug of choice. The truth is every cross-section of society uses it. Male or female, straight or gay, White or Black, poor or rich, educated or illiterate, there is no demographic that only uses it.