Okay my turn.
First off lionfish and scorpionfish possess venom, they are venomous, not poisonous. Hopefully everyone knows the difference between poison and venom.
Next, lionfish venom contains primarily a large dose of acetylchoiline, and a number of secondary heat labile proteins. The reason lionfish venom does what it does is becuase it overwhelms the local nerves causing intense pain. Remember lionfish use venom as a defensive weapon, they want the harassing fish to move away. So overwhelming pain makes you move away. Unlike a snake which needs venom to paralyze and digest its prey.
Given that if you are tagged by a lionfish, immerse your hand under non scalding hot hot water for at least 30 mins, those heat labile proteins will breakdown and lessen the severity of the sting
Over the 20 yrs I've had lionfish, I've been stung 3 times. Each time by a different species. Each time my fault, usually it occured when i was cleaning the tank and spooked one of the lions who was hiding under/besides rockwork in my tank.
All hurt alot, I mean a real lot, I even made up swear words. I went to the ER the first time back in early 90s, and the doctor had no idea what a lionfish was, nor what to do. So even today if you do go to the ER, bring a printout of the animal and any info you have
frank