I noticed an immediate increase in physical energy beginning the first day of using Rhodiola Rosea 500. A doctor who specializes in ADD had suggested I try "rosavin" for attention deficit problems. I tried another product containing a lower amount of rosavin first, with no noticeable effects. Rhodiola Rosea 500,however, does have noticeable positive effects, with no negative side effects. It also has a noticeable positive energy effect on my libido. And, because my overall energy level is up, it does, in fact, help me to concentrate and to be more mentally focused. This formula has a minimum 3% rosavin content, which is important, and the 500 mg capsules are the highest dosage I could find. This may be why it works so well for me. I highly recommend it as a natural, harmless way to improve mental focus and overall energy.