You really don't just drop dead of a heart attack or your brain melts in a stroke from just smoking one hit like people seem to think. In reality, you simply cannot OD on meth unless you have some pre-existing health condition. Me and my friends have went through literally dozens of points in multi-day binges, that's 1.2 to 2.4 grams easily between us both, and we don't die, despite having done it way too many times and got bloodwork, heart rate, ECG, etc scans regularly and everything is in surprisingly nearly perfect condition, at the very least, averagely good.
If you took like a few grams at once you'd probably vomit or pass out depending how you took it. But seriously, people seem to think it works additively, which is a huge myth. IT is not like for every 100 milligrams you take your heart rate goes up so many points, so a bunch would make it beat so fast it would stop. No, in reality the heart rate, sweating, grinding of teeth, etc, are all just side effects, and while a higher dose might make them worse, some people might not even get them at any dose, and people overstate how much dosage matters with something like a stimulant. 100 milligrams or 400 isn't going to be much different. Once you are spun there's a limit to how spun you can get before it simply doesn't do anything else.
I'm not suggesting you use this to take as much as you want, because you might die from dirty dope or simply go psychotic, but in reality, meth simply doesn't kill people this way. It isn't like heroin or booze where there's a lethal level that makes your heart explode, no, it instead does the same as alcohol, it poisons your bloodstream if there's too much which can kill you from any kind of complication.
My advice to you is do much less and wait 10 minutes or even an hour between hits, as a meth addict on a binge, time goes so fast there's no excuse to not space it out and gauge how you feel. Since the stuff lasts so long, too many junkies go crazy at once and get too spun... sit back and toke on the pipe slow like you'd savour a fine wine, or needle only a bit, snort small lines, etc.