--Lipoic acid is a potent antioxidant and does have considerable blood sugar stabilizing properties--enough so that it has been used as a treatment for diabetics and diabetic neuropathy in Europe for many years, particularly in Germany, where a lot of the initial research on its effects was done. In Germany and most other places in Europe it is a prescribed, rather than over-the-counter, substance.

R-lipoic is a newer generation of lipoic acid. Without getting too chemistry technical, alpha lipoic is composed of both left and right "handed" isomers of the lipoic acid molecule (they are mirror images of each other), and it turns out that the human body, for a number of reasons having to deal with lipid metabolism, can only use the right-handed isomer. R-lipoic is only composed of the right handed isomer, meaning per unit of measure it is more effective and less of it can be taken than alpha lipoic. Most sources I've seen give an equivalence ratio on the order of 6:1 to 10:1; 100mg of alpha lipoic will have roughly the same activity as 600-1000mg of alpha lipoic.

And, as Mrs. D has pointed out, recently there's been an even newer generation of stabilized R-lipoic, which seems to be absorbed more completely than the first generation R-lipoic, so, again, less can be taken to get a particular effect (though I haven't seen any ratio concordances comparing the unstabilized to the stabilized yet).

Being able to take less is not only good from the standpoint of expense, but also from the standpoint of tolerance. I do know people that found taking alpha-lipoic in the therapeutic ranges (300mg up to 1800mg/day) frequently had issues with acidic stomach, as it is best to take lipoic apart from anything else for best utilization. Far fewer people seem to have this problem on the lower doses of R-lipoic.