Believe it or not it's "Berocca". I'm not sure if it's available world-wide but is essentially just a fizzy tablet high in vitamins B and C. I dropped one into my bottle one day (can't even recall why) and noticed quite a difference that ride. I started experimenting with using it or not (generally by forgetting and the recalling the ride later, so I guess a semi-blind study). Weird I know, but definately works for me.