Some people swears that this works by applying a small amount to a cotton ball and dabbing it under the eye at night before going to bed. However, I found that the maker of Preparation H says that it "helps shrink hemorrhoidal tissue and is not meant for the area around the eyes. There is no clinical evidence to support that it reduces eye puffiness."

Also, preparation H has been reformulated. It used to have the ingredient of "live yeast cell" in it, which was supposed to reduce puffiness, but this is no longer even in the new verision. Additionally, bags under the eyes are caused by fluid retention as a result of things like allergies, stress, fatigue. The ingredient in preparation H that reduces swelling of hemorrhoids is a vasocontrictor (phenylephrine HCl) and works by constricting blood vessels. Since eye puffiness is caused by fluid retention and not dilation of blood vessels, it's unlikely to have much effect. Also, the amounts you would put under your eye are so minimal, that it would be unlikely to have an effect from any of the other ingredients.

Some tricks that might work instead include elevating your head at night to minimize fluid retention, avoiding alcohol and salty foods, take antihistimines if you have allergies, remove eye makeup at night to avoid irritation of the eye and skin around it, use a moisturizer at night to avoid dryness, which can also lead to irritation and inflammation.

I hope this helps!