There are side effects of long-term, large amounts of vitamin C. Vitamin C is a water-soluble vitamin that has antioxidant as well as immune-enhancing properties and is used to treat vitamin C deficiency diseases such as scurvy. Long-term, large amounts of vitamin C may cause skin petechiae, bleeding gums, dry skin, and cause curly hair if the drug is suddenly stopped. Therefore, if you take vitamin C for a long time and in large amounts, you should gradually reduce the dosage when you stop taking it. Excessive intake of vitamin C can also cause diarrhea, nausea, vomiting, stomach cramps and other gastrointestinal symptoms.