--100mg/day R-lipoic for a long time, and the effects seem, for me, to be roughly equivalent to those experienced taking I took 600mg/day of alpha lipoic (and my stomach is considerably less acidy when I take the R-lipoic; don't even have to take it with food). It is difficult to know exactly which effects come from the lipoic and which come from other supplements, though; I haven't wanted to single-elimination trials to see just how much each one contributes.

I don't know if there are brand differences in effectiveness (I tend to get mine from Swanson Vitamins and use the in-house brand there); perhaps someone else can respond as to that.