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Possible side effects

• The most common complaints are diarrhea, nausea, abdominal cramps, and other digestive upset.

Serious risks

• High intakes may raise urinary oxalate and uric acid, which could contribute to kidney stones, especially in people with renal disorders.
• The best evidence that vitamin C contributes to kidney stones is in patients who already have hyperoxaluria.
• In people with hereditary hemochromatosis, long-term high doses could worsen iron overload and cause tissue damage.
• A few in vitro studies suggested that supplemental oral vitamin C, acting as a pro-oxidant, could cause chromosomal or DNA damage and possibly contribute to cancer.
• In postmenopausal women with diabetes in the Iowa Women's Health Study, supplemental vitamin C of at least 300 mg/day was significantly associated with a higher risk of dying from CVD.

Avoid or ask a doctor first if

• People with hereditary hemochromatosis face a concern about iron overload with chronic high doses.
• The upper limits do not apply to people receiving vitamin C as medical treatment, who should be under a physician's care.
• Infants should get vitamin C only from formula and food.

Medication interactions

• Vitamin C supplements may interact with radiation therapy and with medications, including chemotherapy drugs and statins.
• People taking these medications regularly should talk with their health care providers about vitamin C intake.

Serious risks

• High biotin intakes, possibly even intakes above the AI, may pose a health risk tied to lab testing.
• Biotin beyond recommended intakes can cause clinically significant falsely high or falsely low lab results, depending on the test.
• In a small study of six healthy adults taking 10 mg/day for 1 week, biotin falsely lowered N-terminal pro-brain natriuretic peptide, which could result in a failure to identify congestive heart failure. Thyroid stimulating hormone was also falsely lowered.
• Case reports describe findings falsely indicating Graves' disease and severe hyperthyroidism in patients taking 10–300 mg biotin per day.
• A single 10 mg dose of biotin has interfered with thyroid function tests given within 24 hours.
• Per FDA, a patient with a high intake of supplemental biotin died after a troponin test gave a falsely low result because of biotin interference.

Medication interactions

• Biotin can interact with certain medications, and some medications can have an adverse effect on biotin levels.

Possible side effects

• Raw or unripe elderberries and other elder tree parts can cause nausea, vomiting, and severe diarrhea.

Serious risks

• Large quantities of the toxin in raw or unripe elderberries and other elder parts may cause serious illness.

Avoid or ask a doctor first if

• Little is known about whether elderberry is safe for health purposes during pregnancy or breastfeeding.

Medication interactions

• People who take any type of medicine are told to talk with their health care provider before using elderberry or other herbal products, because some herbs and medicines interact in harmful ways.

Possible side effects

• High zinc intakes can cause nausea, dizziness, headaches, gastric distress, vomiting, and loss of appetite.

Serious risks

• Doses of 50 mg or more taken for weeks can interfere with copper absorption, reduce immune function, and lower HDL cholesterol.
• Very high supplemental doses (142 mg/day) might interfere with magnesium absorption and disrupt magnesium balance.
• According to a few reports, overuse of zinc-containing denture adhesive creams can lead to neurological symptoms and anemia.

Avoid or ask a doctor first if

• The upper limits don't apply to people receiving zinc for medical treatment, who should be under a physician's care.
• Zinc-free denture adhesive formulations are available to prevent the effects linked to zinc-containing creams.

Medication interactions

• Zinc may interact with quinolone antibiotics, tetracycline antibiotics, and penicillamine.
• Some diuretics can lower serum zinc by increasing zinc excretion in urine.
• People taking medications regularly should discuss their zinc status with their health care providers.

Possible side effects

• Taken by mouth, ginger can cause abdominal discomfort, heartburn, diarrhea, and mouth and throat irritation.

Avoid or ask a doctor first if

• If you're considering ginger while pregnant, consult your health care provider, as with all herbal supplements.
• Little is known about whether ginger is safe while breastfeeding.

Medication interactions

• If you take any medicine, talk with your health care provider before using ginger or other herbal products, because some herbs and medicines interact in harmful ways.