Similac is an infant formula approved by the FDA for use by infants with inborn metabolism problems or low weight, as an alternative to breast milk, and for infant and toddler growth. Potential side effects include black stools, diarrhea, gas, and stomach swelling. Rare side effects include vomiting, incomplete bowel movements, and stomach pain. Individuals with allergies to arachidonic acid, docosahexanoic acid, or fish products should check with their physician before using Similac. The formula contains key nutrients for infant growth and development and the document provides instructions for safe preparation and storage.