Barnaby Joyce's story is beyond belief. He's a knob, a liar, and frequently drunk on the job. I understand that getting legless (figuratively, and it seems literally for some of us) is a popular Australian part-time. But, to spin a yarn about interaction with medication is a bit of a stretch.
Ask yourself why Barnaby Joyce — not an inexperienced drinker — was drinking heavily if he was on medication he knew had side-effects with alcohol. And ask yourself why he was in the carpark when he was filmed falling-down drunk. I think it's more plausible that Barnaby Joyce intended to drive home while under the influence.