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High doses of folic acid might cause abdominal cramps, diarrhea, rash, sleep disorders, irritability, confusion, nausea, stomach upset, behavior changes, skin reactions, seizures, gas, excitability, and other side effects.
Preliminary research suggests folic acid might increase the risk of heart attack in people who have heart problems. Other preliminary research suggests high doses might increase the risk of cancer. There is also concern that taking large amounts of a multivitamin plus a separate folic acid supplement might increase the chance of developing prostate cancer in men.
When used in recommended amounts, folic acid is safe for pregnant or breast-feeding women. For pregnant women, 600 mcg per day is recommended. For breast-feeding women, 500 mcg per day is recommended.
Do not use folic acid in doses greater than 400 mcg per day without medical advice if:
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.