Folic acid Side Effects

Not all side effects for folic acid may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to folic acid: capsule, injectable, solution, tablet

In addition to its needed effects, some unwanted effects may be caused by folic acid. In the event that any of these side effects do occur, they may require medical attention.

If any of the following side effects occur while taking folic acid, check with your doctor or nurse as soon as possible:

  • Fever
  • general weakness or discomfort
  • reddened skin
  • shortness of breath
  • skin rash or itching
  • tightness in chest
  • troubled breathing
  • wheezing

For Healthcare Professionals

Applies to folic acid: compounding powder, injectable solution, oral tablet


Gastrointestinal side effects have been reported rarely. They have included anorexia, nausea, abdominal distention, flatulence, and bitter taste.

Gastrointestinal side effects have been reported among patients with doses of 15 mg/day.

Nervous system

Nervous system side effects have included sleep disturbances, concentration problems, irritability, anxiety, depression, confusion, and impaired judgment.

Parenteral administration of high doses of folic acid have been associated with increased seizure activity in patients with epilepsy.

Nervous system side effects have been reported in some patients who were taking 15 mg/day.

Daily doses of folic acid > 100 mcg/day can obscure pernicious anemia in that hematologic remission can occur while neurologic signs and symptoms progress.


Hypersensitivity side effects have been reported rarely. They have included erythema, rash, pruritus, malaise, dyspnea with bronchospasm, and a single case of apparent anaphylaxis.


Metabolic side effects have included impaired gastrointestinal absorption of zinc.

A measurable decline in plasma zinc has been associated with folic acid dosages as low as 400 mcg/day.

Zinc is an intrinsic part of at least 70 metalloenzymes and other cellular components, and is essential for the synthesis of protein, DNA, and RNA. While zinc deficiency is rare, it may become a problem during pregnancy or with patients who have inflammatory bowel disease, malabsorption, liver cirrhosis, and high alcohol intake. Zinc deficiency usually presents as diarrhea; mental irritability; depression; skin lesions of the face, perineum, limbs, and skin folds; alopecia; loss of taste; and defects in the immunologic system.

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