The maximum daily adult dosage of both regular and extended-release guaifenesin is 2.4 grams. It is generally recommended that adults take between 200 and 400 milligrams (mg.) of regular guaifenesin, every four hours. While it is unlikely that you will overdose on guaifenesin, you can minimize your risk by taking only one guaifenesin-based medication at a time and by following package dosing instructions carefully, especially when giving this medicine to children.Children's doses of regular guaifenesin depend on age and the type of guaifenesin being administered. Children four to five years of age may take 50 to 100 mg. of regular guaifenesin every four hours for a maximum daily dose of 600 mg. Children six to 11 years of age may take 100 to 200 mg. of regular guaifenesin every four hours for a maximum daily dose of 1.2 grams. Children 12 years of age and older may take adult doses. Call your doctor if you have any questions about using guaifenesin, especially if giving it to a child.