[VX REQUEST] Determine party leader

[Dissentrix]

Hello again, and sorry for posting two requests at once. But in my game, there's a drug system that is central to the gameplay. Now I've pretty much got it down with common events and a slow-mo script, but the drug would have to be useable only by the party leader. Also, since there's a common event that controls the effects of the drug each time it is used, I need a way to determine who is the leader exactly.
I know in RMVX Ace there's a variable for precisely that, but I don't think it exists in RMVX. So do I have to use scripts ? Which one would that be ?
I have a second question, which is related to the first one : is there any way to make an event affect only the leader of the party ? As in, the drug common event. Can I only have it affect the party leader ?
Any help or input, of any kind at all, is appreciated.