The R-form of alpha-lipoic acid is the active, natural form. The S-form occurs when alpha lipoic acid is synthetically manufactured, creating both the S-form and the active R-form. The S-form is most likely inactive, although some information suggests it may an analgesic effect. For more information, see the What It Is section of our Alpha Lipoic Acid Supplements Review, which includes our Top Picks.
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