I don't know about pigs high on drugs/chemical agents, but the pigs where I used to live in Devon England were often falling down drunk for around two weeks of the year. Yeah, our local pig farmer used to keep his pigs in cider apple orchards (supplying cider producers being the 2nd bow to his fiddle) and the pigs would eat the over-ripe apples that had fallen from the trees and fermented in the summer sun.
Yup, they were pretty smart pigs! They wouldn't eat the fallen apples straight away, but instead would leave them laying on the ground for a few weeks until they were fermented before eating them, thus resulting in several drunken pigs. There wasn't a lot to do in a village of around 800 - 900, entertainment wise, so we made our own... and each year my mates and I would make our annual pilgimage to the piggery to sit on the apple orchards stone walls and watch the drunken pigs for laughs. One, however, did not dare go into the orchard as the pigs could get quite aggressive, one old boar in particular, because it was seen as a threat to their grog supply.
Ah, the good old days... drunken pigs and scrumpy.