well meth is a little different, i think, as I've smoked and injected both substances and while IV heroin is obviously WAAY more euphoric and addictive than when smoked, smoked meth seems to be more addictive, while less euphoric, than injection. it also hits slightly faster, by about 20 seconds. meth hits you literally as you exhale, while when i shot meth, i expected it to hit me even quicker. i actually stood up and said to my friend "dude, this isn't working, this shit's bunk!" but before i could finish, i was floored haha
oddly enough, there was absolutely zero impulse to redose, and there wasn't much of a crash from that either. the high was like 8 hours too, which confuses me, as IV drugs tend to be short-lived. Smoked meth has like maybe 30-45 minutes of duration, followed by effects that are hardly noticable enough to call a "high" lasting anywhere from 4-24 hours, thus making it fiendy and giving you an intense impulse to redose, similar to crack or snorted cocaine, but way more intense IMO. Then you get in the cycle of smoking meth to fix the crash from smoking meth, which usually lasts until the substance is all gone.