The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.


Avoid if sensitive or allergic to any ingredients present in Vitamin C products.

Side Effects and Warnings

Vitamin C is generally regarded as safe in amounts normally obtained from foods. Vitamin C supplements are also generally regarded as safe in most individuals in recommended amounts.

Vitamin C may cause abdominal cramps or pain, chest pain, dental erosion, dizziness, diarrhea, faintness, fatigue, flushing, gut blockage, headache, heartburn, increased risk of lung cancer, increased risk of Parkinson's disease, inflamed esophagus, injection site discomfort, nausea, red blood cell complications, skin tingling or irritation, slowing of endurance training, thickening of blood vessels close to the heart, urinary complications, and vomiting.

High doses of vitamin C have been associated with multiple adverse effects. These include blood clotting, death (heart-related), kidney stones, pro-oxidant effects, problems with the digestive system, and red blood cell destruction. In cases of toxicity due to massive ingestions of vitamin C, forced fluids, and diuresis may be beneficial.

Use cautiously in chronic, large doses. Healthy adults who take chronic large doses of vitamin C may experience low blood levels of vitamin C when they stop taking the high doses and resume normal intake.

Vitamin C in high doses appears to interfere with the blood-thinning effects of anticoagulants such as warfarin. Caution is advised in people with bleeding disorders or those taking drugs that affect bleeding. Dosing adjustments may be necessary.

Vitamin C may affect blood sugar levels. Caution is advised in people with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.

Vitamin C may increase blood pressure. Caution is advised in people with high blood pressure.

Use cautiously in people with cancer (e.g. lung), cataracts, glucose-6-phosphate dehydrogenase deficiency, anemia and related conditions, disorders of the gut, kidney stones, or sickle cell disease.

Use cautiously in people after angioplasty and in pregnant women at risk of high blood pressure during pregnancy.

Use cautiously in greater than recommended doses in breastfeeding women.

Use cautiously in people taking antibiotics, anticancer agents, HIV medications, barbiturates, estrogens, fluphenazine, or iron supplements.

Use injected vitamin C cautiously, especially in high doses, as it may lead to kidney function problems.

Use vitamin C tablets cautiously, as dental erosion may occur from chewing vitamin C tablets often.

Avoid in people with known allergy or sensitivity to any ingredients in Vitamin C products.

Avoid high doses of vitamin C in people with conditions aggravated by increased acid, such as advanced liver disease, gout, a disease where kidneys fail to remove extra acid from the body, or a disease with early breakdown of red blood cells.

Avoid high doses of vitamin C in people with kidney failure or in those taking agents that may damage the kidneys.

Pregnancy and Breastfeeding

Vitamin C intake from food is generally considered safe during pregnancy and breastfeeding.

Use cautiously in greater than recommended doses in pregnant and breastfeeding women.

Use vitamin C cautiously in those at risk of high blood pressure during pregnancy.

This evidence-based monograph was prepared by The Natural Standard Research Collaboration