The medical form is essentially a doctor's verification for special services while on the ship. Examples might include a refrigerator for insulin or other medications (colder than the "beverage cooler" that is in all the rooms), an assignment to a handicapped cabin, an IV infusion of needed medications, etc. You do not need this form do not know in advance that you need the ship's medical services or have special medical needs.
You do not need this form just because you take regularly prescribed medications. Just bring your medications in an original container from the pharmacy. I save my past container and count out the exact number that I'll need for the trip--yes, I could drop one or whatever, but that way there is no issue of bringing them back and I know that I have enough left when I get home.