Although theobromine is related to caffeine and exerts similar effects, theobromine does not affect the body through central nervous system stimulation. Instead, it induces muscular relaxation of the smooth muscle tissue. However, the presence of an additional methyl group increases its half-life and slows system clearance - thus making its effects longer lasting.[/B]
It works by acting on the nerves in the veins, and causing them to relax in order to allow more blood to flow. For this reason, combined with its mild stimulating effect, Theobromine offers benefits to athletes, and will allow you to work at a high intensity for much longer than otherwise."
I have used Ultra Reps very late in the evening and had no problems with sleep. Keep in mind each individual is different. I honestly don't believe it is enough to really cause a problem. Thanks for the question.