Vitamin C

Proposed therapeutic uses

Water soluble antioxidant. Numerous studies have shown that vitamin C can reduce the length of and severity of cold symptoms. Evidence also suggests that regular use can reduce the risk of cataracts and macular degeneration. Some studies have indicated that it may help reduce blood pressure modestly. It also acts to potentiate the effect of vitamin E to decrease the risk of developing atherosclerosis.
Sources
Red chili peppers, sweet peppers, kale, parsley, collard, turnip greens, broccoli, brussle sprouts, watercress, cauliflower, cabbage, and strawberries, as well as citrus fruits.
Therapeutic dosage
500 - 1000 mg per day (in divided doses) routinely. This may be increased to 3000 - 5000 mg per day in multiple divided doses during periods of stress or illness.

Complementary with vitamin E.

Safety concerns
Diarrhea can occur at high doses (>2000 mg), but stops upon decreasing the dose. Excessively high doses can cause copper deficiency and increased iron absorption. You should avoid high doses if you have kidney insufficiency or failure, glucose-6-phosphate dehydrogenase deficiency, iron overload or have had intestinal surgery.
Interactions
Aspirin, Non Steroidal Anti-inflammatory Drugs (NSAIDS) such as Motrin, oral contraceptives, estrogen, phenobarbitol - you may need extra vitamin C. Vitamin C may increase the levels of aspirin and salicylates in your blood. High doses may interact with Coumadin and heparin, lowering their blood thinning effects. High dose vitamin C can increase iron absorption. Copper absorption may be impaired.