G.K.
That depends on a lot of things. How old is your baby? Is your baby gaining? Why do you think you need the supplement? Those are the 3 biggest questions I would ask if I were counseling a mama (I'm a peer counselor with Nursing Mothers Counsel). Any time you have a breastfeeding question, please feel free to use us as a resource! Our website is http://www.nursingmothers.org, and there are a couple other really good websites like drjacknewman.com and kellymom.com.
I also wanted to add that babies and toddlers ALWAYS benefit from mom's breastmilk!! It's always changing with the age of the baby, so it's always nutritionally appropriate. Your milk will also have antibodies beneficial to baby as long as you nurse, and recent research has shown that your milk will actually increase in antibodies when your child is around age 2, so those benefits are continuous.