What’s the difference between caffeine and caffeine anhydrous?
The difference has to do with the amount of water associated with the caffeine molecule. The term "caffeine" can refer to any form of caffeine, regardless of its water content. “Caffeine anhydrous" has essentially no water—just 0.5%. For this reason, logic and chemistry suggest that anhydrous caffeine is more potent. The anhydrous form could also be more potent because, according to some evidence, the body may absorb it more readily. For all intents and purposes, however, caffeine and caffeine anhydrous are synonymous.
The form of caffeine that appears most often on dietary supplement labels is caffeine anhydrous. Other names for caffeine include 1,3,7-trimethylxanthine and methyltheobromine but caffeine in dietary supplements can come from “hidden” sources too. For more information, read the OPSS FAQ about hidden sources of caffeine.
The Food and Drug Administration (FDA) requires food and dietary supplement manufacturers to identify caffeine in the ingredient list of a product that contains added caffeine in any form.