None. It is a natural chemical used by your brain to regulate sleep. You won't absorb too much of it, so it may not have any effect if you are not low on it.

Some people notice being a little groggy in the morning when they first start taking it, but I believe that's because your body has been sleep deprived previously, and that feeling did not last more than a few days for me.

I take the gummies to promote absorption.