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Folic acid: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on July 14, 2022.

1. How it works

  • Folic acid is a B group vitamin; another name for it is vitamin B9. Folic acid has several important functions in the body including maintenance of a normoblastic marrow, the synthesis of nucleic acids, the conversion of carbohydrates into glucose, the utilization of fats and protein, and it is important during periods of rapid growth and development, such as during pregnancy, in infancy, and in adolescence.
  • The supplement, folic acid, is a synthetic version of folate, the natural form of vitamin B9 that is found in a wide variety of foods such as leafy green vegetables, asparagus, beans, beets, broccoli, Brussel sprouts, liver, kidneys, oranges, peas, salmon, spinach, whole-wheat products, and yeast.
  • Folic acid/folate deficiency is relatively common, particularly among people who regularly drink alcohol, during pregnancy, in inflammatory bowel disease, or Celiac disease. Symptoms of folic acid deficiency include gingivitis, poor appetite, poor growth, neural tube defects in babies, shortness of breath, and tongue inflammation. Folic acid deficiency may also cause diarrhea, irritability, forgetfulness, and mental sluggishness.
  • Folic acid belongs to the class of medicines known as vitamins. It is specifically a B vitamin.

2. Upsides

  • Used to treat megaloblastic anemias due to folic acid deficiency as seen in absorption disorders such as nontropical and tropical sprue.
  • May treat anemias of nutritional origin, pregnancy, infancy, or childhood.
  • Used in combination with other medications to treat vitamin B12 deficiency (can lead to pernicious anemia). Folic acid/folate and vitamin B12 are both needed in the production of red blood cells and iron utilization.
  • Can prevent the development of neural tube defects (such as spina bifida and anencephaly) in women that may occur within 3-4 weeks of conception (before most women even realize they are pregnant). Because half of all pregnancies are unplanned, all women of child-bearing age should consume 0.4 mg (400 micrograms) of folic acid daily.
  • Relatively nontoxic.
  • Helps control blood levels of the amino acid, homocysteine, in conjunction with other B-vitamins.
  • Consuming recommended levels of folate in the diet may help protect against heart disease, although it is not clear if taking folic acid supplements has the same effect.
  • Generic folic acid is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Side effects, such as nausea, abdominal pain, skin reactions, sleep problems, loss of appetite, or seizures are rare and more likely with higher dosages.
  • Do not use in people who have shown previous intolerance to folic acid.
  • High levels of folic acid may mask vitamin B12 deficiency, so talk with your doctor before taking folic acid. Folic acid supplementation should be combined with vitamin B12 supplementation in people who have megaloblastic anemia or pernicious anemia with vitamin B12 deficiency.
  • All of the B vitamins, including folic acid, are water-soluble; which means that the body does not store them. A regular intake is required.
  • Liquid preparations of folic acid are heat sensitive and rapidly decompose in the presence of light or riboflavin.
  • People with cancer or who have seizures or who take certain medications such as tetracycline (an antibiotic), phenytoin, Daraprim, and some chemotherapy medicines should talk with their doctor before taking folic acid, because of the potential for interactions. Some other medications may interfere with the effectiveness of folic acid.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Folic acid is the synthetic form of folate (also called vitamin B9) which is necessary for proper growth and development and several other vital bodily processes. All women of child-bearing age should consume 0.4 mg (400 micrograms) of folic acid/folate daily, in the form of folate-rich or fortified foods, or as a supplement.

5. Tips

  • Take folic acid supplements with a full glass of water, either with or without food.
  • Take as directed. Dosages may vary depending on age and pregnancy/breastfeeding status. Do not take more than recommended. If you are taking folic acid because you are deficient in folate, the dosage of folic acid may also decrease as your deficiency reduces.
  • Even if you are not planning on having a baby, if you are a woman of child-bearing age and capability, then you should consume 0.4 mg (400 micrograms) of folic acid daily.
  • If you are concerned about your risk of developing heart disease, ensure your diet contains adequate levels of B vitamins in the form of vitamin B-rich foods.

6. Response and effectiveness

  • Folic acid is rapidly absorbed from the small intestine and appears in the plasma within 15 to 30 minutes after an oral dose. Peak levels are reached within an hour of a single dose.
  • Levels of folic acid in the cerebrospinal fluid are several times greater than in the blood.
  • Water-soluble, so the body does not store it; therefore daily intake in the form of folate-containing foods or folic acid supplements is necessary.
  • Taking folic acid around the time of conception and for the first 12 weeks reduces the risk of neural tube birth defects by 72% to 100%. There is some evidence that folic acid supplementation during pregnancy also reduces the risk of miscarriage, autism development, and language delay.
  • Some studies suggest folic acid may protect against age-related hearing loss, age-related macular degeneration, and some forms of cancer. The benefits of folic acid for the treatment of depression are not clear.

7. Interactions

Medicines that interact with folic acid may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with folic acid. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with folic acid include:

  • anticonvulsants, such as carbamazepine, Divalproex, phenytoin, and phenobarbital
  • chemotherapy agents, such as capecitabine and fluorouracil
  • methotrexate
  • nitrofurantoin
  • pancreatin and pancrelipase
  • pyrimethamine
  • rufinamide.

Research suggests the anticonvulsant action of phenytoin is antagonized by folic acid. A person whose epilepsy is controlled by phenytoin may require an increased dose if folic acid is given.

Folic acid deficiency may be caused by the administration of folic acid antagonists, such as methotrexate, anticonvulsants (such as primidone and barbiturates), alcoholic consumption, alcoholic cirrhosis, pyrimethamine, or nitrofurantoin.

Note that this list is not all-inclusive and includes only common medications that may interact with folic acid. You should refer to the prescribing information for folic acid for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use folic acid only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: July 14, 2022.