What vitamins are good for constipation?

Magnesium is the best vitamin for constipation. This is because it works in two ways. The first is through osmosis (bringing water into the colon for softer stools) and the second is by calming the nervous system to allow it to relax and have regular bowel movements.

I don't know if you would call a probiotic a vitamin, but that will also help with constipation. Look for any probiotic that has species that start with "Bifido" - those are the ones most commonly found in the colon and will help relieve constipation over the long-term.