I think Therin is right, that's the way its alluded to in the series. Additionally, in the novel 'Atricles of the Federation' it describes one of the reporters going through several bottles of synthehol based drinks and then (I think) taking a pill to neutralise the effects. Interestingly, I believe, something like this has been speculated about it real life. Obviously, it wouldn't be alcohol based but would simulate the effect.