Hello. Folic acid is LIKELY SAFE for most people when taken by mouth or injected into the body. Most adults do not experience any side effects when used in doses less than 1000 mcg daily. Folic acid is POSSIBLY UNSAFE when taken by mouth in large doses, long-term. 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. There is some concern that taking too much folic acid for a long period of time might cause serious side effects. Some research suggests that taking folic acid in doses of 800-1200 mcg might increase the risk of heart attack in people who have heart problems. Other research suggests that taking these high doses might also increase the risk of cancer such as lung or prostate cancer. Special Precautions & Warnings: Pregnancy and breast-feeding: Folic acid is LIKELY SAFE when taken by mouth appropriately during pregnancy and breast-feeing. Taking 300-400 mcg of folic acid daily is commonly used during pregnancy to prevent birth defects. Procedures to widen narrowed arteries (angioplasty): Using folic acid, vitamin B6, and vitamin B12 intravenously (by IV) or by mouth might worsen narrowed arteries. Folic acid should not be used by people recovering from this procedure. Cancer: Early research suggests that taking 800-1000 mcg of folic acid daily might increase the risk of cancer. Until more is known, people with a history of cancer should avoid high doses of folic acid. Heart disease: Early research suggests that taking folic acid plus vitamin B6 might increase the risk for heart attack in people with a history of heart disease. Anemia caused by vitamin B12 deficiency: Taking folic acid might mask anemia caused by vitamin B12 deficiency and delay appropriate treatment. Seizure disorder: Taking folic acid supplements might make seizures worse in people with seizure disorders, particularly in high doses. with regards- Dr Sanjay Kini