Folic Acid Side Effects

Medically reviewed by Drugs.com. Last updated on Dec 28, 2023.

Applies to folic acid: capsule, solution, tablet.

Serious side effects of folic acid

Along with its needed effects, folic acid may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor as soon as possible if any of the following side effects occur while taking folic acid:

Rare

• 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

• Rare (less than 0.1%): Mild gastrointestinal upset, nausea, abdominal distension, flatulence^[Ref]

Nausea, abdominal distension, and flatulence were reported in patients taking 15 mg folic acid daily for 1 month.^[Ref]

Nervous system

• Frequency not reported: Bitter or bad taste, altered sleep patterns, difficulty concentrating, overactivity, impaired judgement, increased incidence of seizures in some epileptic patients^[Ref]

Bitter or bad taste, altered sleep patterns, difficulty concentrating, overactivity, and impaired judgement were reported in patients taking 15 mg folic acid daily for 1 month.

Increased seizure incidence was seen in some epileptic patients receiving phenobarbital, primidone, or diphenylhydantoin.^[Ref]

Hypersensitivity

• Rare (less than 0.1%): Allergic responses (including erythema, skin rash, itching, general malaise, respiratory difficulty due to bronchospasm), anaphylaxis (including shock)^[Ref]

Metabolic

• Rare (less than 0.1%): Anorexia
• Frequency not reported: Decreased vitamin B12 serum levels, worsening symptoms of B12 deficiency^[Ref]

Anorexia was reported in patients taking 15 mg folic acid daily for 1 month.

Decreased vitamin B12 serum levels was reported with prolonged folic acid therapy.^[Ref]

Other

• Frequency not reported: Decreased diphenylhydantoin serum levels^[Ref]

Decreased diphenylhydantoin serum levels were reported in patients taking 5 or 15 mg folic acid daily.^[Ref]

Psychiatric

• Frequency not reported: Irritability, excitement, mental depression, confusion^[Ref]

Irritability, excitement, mental depression, and confusion were reported in patients taking 15 mg folic acid daily for 1 month.^[Ref]

Frequently asked questions

• Why should I take folic acid with methotrexate?

Further information

Folic acid side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.

Medical Disclaimer