Not finding any success in the self help and fitness books, a guy goes into a magical store and is given a remedy that works but comes with challenges and side effects that he wasn’t prepared to confront.

Yeah think we need to know what some of the issues he will be facing. Also his motives for using the magic store other than being overweight. Has a woman turned him down due to it causing him to try lose the weight? DO the side effects effect relationships or him internally? I can see connections to The Nutty Professor. He was taunted so devised a potion and the side effects were 'Buddy Love'. Perhaps use an example from The Nutty Professor to help you structure it.

Thanks for the tip. Let me rewrite this one based on your feedback.

I have no idea what the "guy" is trying to be successful at. What sends him to the "magical store"? And I think we kind of need to know what side effects he will need to deal with, because that sounds like "the hook" (what makes the audience want to see this movie?) to me.