Well...I'm not one to just automatically trust a product that goes directly on your forehead to get rid of a headache, so I googled the side-effects. However, all I'm coming up with are side-effects of giving head. And I don't want to give head. Not right now, anyway.
So, I put it to you, Dr. LJ. Are there any known side-effects to Head On? Other than annoying repetition, I mean.