I never heard anything about the superhuman strength part, but I know people can get sh whacked out on it that they don't really feel pain and if they're in a fight they don't stop until they literally can't go anymore. I've personally seen that twice.
the pain part according to this controlled test is legit, it deadens the nerves or some shit...but at one time drug warriors were claiming that dust gave bros superhuman strength, like they could lift cars and shit, and this study crushed that bs