No medication at all exists anywhere in this universe that creates fat magically out of thin air without an excessive consumption of calories.

That would defy all laws of physics and biology at it's very core.

Some medications can have a slight depression of your metabolism, but that's corrected through increasing activity and reducing calories consumed.

Medications can cause water retention, which there are meds to fix that. But generally it's only a couple pounds, and that's handled by a salt reduction or a change in medication as anything beyond a few pounds can be dangerous in itself. The one outlier would be runs of corticosteroids like Prednisone which for sure can make you hold 20 pounds of water, but outside of extreme illnesses runs of that medication rarely last longer than a couple weeks.