I've found the quality of the liquor makes a big difference.
Back when I was still drinking, we all went out to our favorite bar to try out their power hour special one night. (Most) well drinks were $1/each. Looking back, I don't remember how much I had, but it wasn't all that much considering we went there at 8:30 and power hour was over at 9. If I had to ballpark it, it was probably 6 rum and cokes and maybe 3 beers. The well rum was TERRIBLE, possibly the worst I've ever had. Normally that's not enough to give me a hangover, but the next morning my head hurt so bad I had to lay in bed for two hours before I could even move.
Another time I drank half a bottle of Cuervo 1800 by myself, the next day my stomach hurt a little, but it wasn't all that bad.
I don't think this Chaser stuff is RU-21 (because that's only recently been approved), but at least that has FDA backing.