I have been into fisting for the last three years. I have only ever used poppers. I must say, a new bottle is best as it gives you more of a hit.
Like with all chems (including prescribed) you have to be careful they don't mask any other pain apart from the sphincter muscle. I have always found its best to work my way up through butt plugs. Lots of good lube (J-lube i have found is best) and someone who knows what there doing.
I had a point where i was near to taking a fist but couldn't quite get past the thumb knuckle joint, if the top has got anything about them a good slap on the back or ass to take your mind of your ass briefly will do the trick.
I've seen guy on Meth and i find them boring cos they can never play because they're soft, there again when i'm being fisted, like most people, i go soft.