There is no iron supplement that is completely free of side effects. However, different forms of iron supplements can cause different types and levels of side effects. If you are experiencing digestive side effects like constipation, diarrhea, nausea, or stomach irritation with ferrous sulfate, you may want to try other forms of iron such as ferrous fumarate or Feramax. It's also helpful to take iron supplements with food to increase tolerance, and consider adjusting the dose or frequency while trying to maximize absorption, for example by taking it with vitamin C. It's important to discuss these options with your pharmacist or doctor to find the best solution for you.