Common side effects of Emergen-C include stomach discomfort, diarrhea, headaches and vertigo, explains Drugs.com. Serious side effects caused by the mineral content in the supplement include blurry vision, breathing difficulties, excessive thirst and vomiting. It is important to seek immediate medical treatment if severe side effects occur.
Women who are pregnant or nursing should consult with a physician prior to taking Emergen-C supplements, according to the Emergen-C website. Individuals who are taking prescription medications should also seek medical advice prior to consuming the supplement. When taking Emergen-ZZZ, the nighttime sleep aid formulation of Emergen-C, individuals should not drive or operate machinery due to the melatonin content in the supplement.