I recently bought a product at GNC called P6, pretty expensive but got good reviews on increased libido, energy, and improved work outs. I started out with a half dosage but even then I noticed that it made me "wired" (no caffeine in it like other work out supplements). I have insomnia already, so I stopped using it after a couple of days of disruption in my sleep cycle. Now I'm back to my regular routine, coffee before lifting weights and 25/50 mg. Viagra before sex.