Something as simple as grapefruit can actually harm your health if you're taking some very common drugs. Everyone should eat more fruit and veggies, right? Well, if you're taking a prescription medicine, it's not always that simple. For example, grapefruit can actually harm your health if you're taking some very common drugs. So, in addition to asking your doctor for help, get tips from Dr. Madelyn Fernstrom, Today Show nutrition and diet guru. She discusses her new book, Don't Eat This If You're Taking That, a complete guide on foods to avoid and easy diet swaps. Bonus! Surviving the Flu: Symptoms, Treatment, and Danger Signs