I sourced fentanyl as part of a plan to CTB. I ended up trying it out of curiosity, and damn well does it ever take away the urge to die. In a way, it saved me for awhile because I didn't feel suicidal when I was high.
I did end up ODing accidentally, so it's not difficult to reach that threshold. Closest I've been to death, and damn was it ever peaceful. It took about 5 minutes to black out, and before that it was rather tranquil. I remember going downstairs to go get some food, but sure enough it was like BAM, out like a light. If it wasn't for me having been walking down the stairs at the time of the OD, and well falling down the stairs and making a loud bang upon fitting the floor, I wouldn't have been seen and Narcan'd. No permanent damaging effects.
Heroin would be marginally more euphoric, maybe a little itchy, but would require a MUCH greater amount. 2grams could be enough, but still unlikely to be so because of it's almost always incredibly cut.
Even fentanyl to an extent, is super cut on the streets and DNMs.
Don't message me for sources.