I watched GB last night while recuperating from an injury and I still cannot figure this scene/line out!
Venkman: “I just whacked her up with about 300cc's of thorazine..she's gonna take a little nap now…”
So where'd it come from?

It's an antipsychotic that causes sedation.

http://en.wikipedia.org/wiki/Chlorpromazine

mr pecker;171218
It's an antipsychotic that causes sedation.

http://en.wikipedia.org/wiki/Chlorpromazine

Yes, my fellow Ghosthead..already know what the drug is used for…I wanna know Where Venkman Got It To Give Her In The First Place.

Ha….well….he's a doctor? And it's a movie?

I believe when this has come up in the past it was noted he might have access to it from his degree, however why he was already carrying it with him is another story.

The fact that he Venkman was already carrying a sedative with him to go on a date with Dana has been a point of humor for many for years now. In reality it was probably a result of a bad edit or storyline oversight…but it DOES make for some interesting stories…no?

It's Venkman's B-plan for getting them in the sack at the end of the night….

Maybe Louis gave it to him…

I've been going back-and-forth with IMDb on this. By my thinking, there are only three possible methods of getting the thorazine to Dana's apartment:

1) Peter brought it with him… which creates some interesting questions as to his plans for the evening.

2) Peter left to get it… which seems unlikely given Zuul was very eager to keep him there.

3) Dana had it there already… creating another explanation for what she saw in the fridge.

All of which ignores the fact there's no LEGAL way to obtain thorazine; my research shows it's dispense-only, meaning it's not allowed out of the medical facility. Additionally, Venkman's a Ph. D, not an MD, so he's not licensed to administer medication. I mean, his ethics are questionable, but not THAT questionable.

Which makes me go back to my plot oversight theory.

More than likely it's a case of “they needed the name of a sedative and came across the name some how without investigating it any further”