Capsule:Vitamin C: Vitamin C is usually tolerated, However, nausea, vomiting, heartburn, abdominal cramps, fatigue, flushing, insomnia, and sleepiness have been reported with high doses of Vitamin C, particularly ascorbic acid (i.e., 1 g or more daily). Zinc: Gastrointestinal side effects such as nausea and vomiting are seen with doses of elemental zinc greater than 40 mg. Syrup/Oral drops: Acute toxicity may cause diarrhea, vomiting and lethargy.