I've IV'd MET and DPT, a couple times each. I can't help with dosage really, because I'm terrible about letting tolerance fully reset between psych uses, have a natural tolerance, and tend to come down much faster than others, (even during my first use of psychs with friends,) and the few times I did them I was already mildly tripping on something else, which made the experiences go from a + to a +++/+.
As for why it's more powerful IV'ed than IM, even with IM it "trickles" into the bloodstream, much much faster than taking them orally, but still, while with IV it is instantly in the blood (less than 1 minute until it's launching into your brain at full speed.) I remember one time with MET I was just about to withdraw the needle when my entire visual field was enveloped in insane MET visuals already, and I had trouble just throwing the needle in the needle disposal box, and could barely concentrate to put pressure on the puncture site for 30 seconds. Typically with IM, I've found I've enough time to clean up, even take a quick trip to the bathroom before laying back in bed, starting to feel it in 3-5 minutes instead of less than one. That massive rush of whatever drug will just overwhelm your brain much more quickly than even IM.
Fwiw, I've only done those a few times, and I prefer IM by far, it's all just too quick IV imo, and you definitely should have a sitter, or at very minimum, be sitting on your bed, music, lights, etc. already playing. With your needle disposal right there and some cotton or pre opened alcohol swap right there to apply pressure, there's no time to run to the bathroom even just to rinse your mouth out or throw something away. Whatever you choose, good luck : )
Finally for HARM REDUCTION IF YOU DON'T KNOW NEEDLES, hopefully you already know this (but for anyone else who might be reading,) to IM or IV anything you should be using sterile saline solution meant for injection, or better yet bacteriosteric sterile solution, and you should filter the substance through a 0.22 um (micron) filter (as well as use an alcohol swab at the intended puncture spot, 30 seconds starting at the intended puncture site then moving and going outward in a ring shape.) I can't give sources, but these are all cheap and legal in the USA (as far as I know, I'm no lawyer.) Without filtering (and even if filtering, just must less likely than if you don't,) you risk putting in bacteria and dust, and lots of other stuff straight to your blood (IM or IV.) If the wrong bacteria gets in your blood and your body doesn't kill it right away, it can turn into sepsis (an infection of the blood,) and you could be dead in less then 48 hours even with Drs and RNs pumping you (via IV drip) full of multiple of the most powerful antibiotics we have, no matter your age/health before the injection.
While, not drug related, I know a friend who's mom died in her early 40s, she was very healthy, and she got mildly bit on the finger by her cat. And you guessed it, she was dead in less than 48 hours from sepsis (and she'd gone to ER in about 12 hours after the bite,) just from a bite that caused a small trickle of blood but inserted some bacteria. So yeah, if you've never injected something (or if you have, but without fully reading up on it,) DO YOUR RESEARCH, there's more to it than I've said here, with some good guides here on bluelight. Just be careful, yalls : ) Oh, and I guess if you get bit by anything, remember to immediately wash the area for 10 minutes with hot/warm water and soap (regular soap is better than antibiotic soap, hydrogen peroxide is really just a gimmick and never really useful except in very specific circumstances, alcohol is 2nd best if you don't have soap and water within a couple minutes of you.) And then after the bite stay calm, you're almost certainly fine, but if you feel a temp/any fever like symptoms get to an ER asap (or if it's possible the animal that bit you carries rabbles.) Sorry to be a downer, it's rare, but you don't want it to be you!
