From a Times article noting that its OK to deliberate a jury verdict while drunk,

...a 1987 United States Supreme Court decision involving a jury that... drank, used cocaine, smoked marijuana, sold drugs to one another and slept through a trial that one juror called "one big party." In that case, the court ruled: "However severe their effect and improper their use, drugs or alcohol voluntarily ingested by a juror seems no more an 'outside influence' than a virus, poorly prepared food or a lack of sleep."