Ok... Interesting idea Mel...

I am reading a book Spiritual Midwifery - Ina May Gaskin, and the first half is birth stories from a bunch of hippies. I am not sure of the drug states of them giving birth, but they do talk a lot about being high and having releases and being psychedelic (I am sure some of this is hippy jargon) but thes birth stories do also talk alot about emotional states of birthing mothers, and finding that emotional release and then whoosh out comes the baby.

So, in that way, if your labour was stalling due to an emotional blockage, which I believe from recent research is a real thing, and you felt pot was the way to release, the I would think it is fine.