Folic Acid Side Effects

Folic Acid Side Effects


In numerous informative texts and articles we read that folic acid – improperly called vitamin B9 for some  – is a safe, water-soluble molecule which does not produce side effects.

Of course, adequate supplementation of this very important vitamin , specific to the needs of the individual, can only bring important benefits to the body.

Note : what many advertising channels do not specify is that folic acid can cause unpleasant side effects even when taken in excess.Just think, for example, of the importance of regular folic acid supplementation during pregnancy : vitamin B9 is in fact necessary for the growth and correct development of the unborn child, as well as for the prevention of terrible anomalies such as spina bifida . Furthermore, a supplementation of folic acid can minimize the risk of cardiovascular pathologies in patients subject to this kind of disturbance (especially in the case of high cholesterol and homocysteine ​​values ).

However, the skill and cunning of some advertising propaganda and certain Internet sites seem to make fun of potential customers, exploiting their credulity and ingenuity to encourage them to take megadoses of folic acid in order to prevent possible (and terrible) risks “from deficiency “, on which particular (and excessive) emphasis is placed. It is clear that, pressing one’s hand on the possible effects produced by a lack of folic acid , the potential client is frightened by convincing him that it is better to exceed the doses, in the mistaken belief that “it doesn’t hurt anyway”.

What is it and Benefits

Folic acid is the folate supplement, molecules necessary for the life and survival of the human body.

They play a key role in the production  of  nucleic acids  ( DNA  and  RNA ) and in the  metabolism  of certain  amino acids , both factors required for   cell replication .

Side effects

Folic acid is a safe molecule and does not produce any side effects when taken within the doses recommended for one’s health and age.

Recommended doses

Indicatively, the recommended doses are:

  • 200-300 µg* (0.2 – 0.3 mg) in adults;
  • 400-500 µg (0.4 – 0.5 mg) in pregnancy;
  • 350 µg (0.35 mg) during lactation .

*µg = mcg

For the treatment of certain cardiovascular pathologies , some doctors recommend taking folic acid in higher quantities, in the order of 400-1000 µg per day.

Some pregnant women particularly at risk of folic acid deficiencies even require 5 mg (5000 µg) of folic acid per day (to be taken in the form of supplements ).

Despite this, pregnant women are advised to scrupulously respect the doses of folic acid prescribed by the doctor: in fact, some side effects have been reported in the newborn following an exaggerated integration of vitamin B9 by the mother during pregnancy.

In these children, a higher incidence of asthma and wheezing has already been recorded during the neonatal and childhood age.


What if blood folic acid is high?

Although the risk of toxicity from excess folic acid is relatively low, it is still advisable to consider what side effects an exaggerated surplus of this vitamin could generate.

With the exception of some pregnant women who are particularly at risk of folic acid deficiencies, in healthy adults, an intake of vitamin B9 greater than 400-1000 mcg/day could cause side effects of overdose.

The table shows the most common overdose risks and possible (albeit rather rare) side effects.

Common side effects of folic acid overdose (doses > 400 mcg/day but less than 1000 mcg) Rare side effects of folic acid overdose (doses > 1000 mcg/day)
  • Alopecia
  • Mood alteration
  • Skin redness
  • Increased risk of erythema
  • Cramps
  • Depletion (loss) of zinc
  • Diarrhea
  • Rash and red spots on the skin
  • Flatulence
  • Bitter taste
  • Nausea
  • Urticaria
  • Dry /flaky skin
  • Itching
  • Stomatitis
  • Change in the natural color of urine (their color becomes more intense)
  • Impaired ability to express one’s opinion
  • Increased frequency of seizures in patients with epilepsy
  • Sleep disturbances ( insomnia )
  • Excitability
  • Hyperactivity
  • Irritability
  • General malaise
  • Recurring dreams and nightmares
  • Involuntary spasms of the body with momentary loss of consciousness

Very large doses of folic acid can cause serious side effects on the central nervous system .
Epileptic patients taking high doses of folic acid risk exacerbation of seizure symptoms .
Furthermore, we must not forget that an excess of folic acid could hide the symptoms of blood diseases such as pernicious anemia , a pathology caused by a protracted and untreated vitamin B12 deficiency . This form of anemia, whose symptoms are precisely hidden by an overdose of folic acid, could cause serious neurological disturbances to the victim, such as the appearance of paresthesias, loss of sensitivity and, in the most serious cases, total paralysis.

Drug interactions

Some patients must be especially careful when taking folic acid supplements , since vitamin B9 could cause unpleasant side effects in the body following interaction with certain drugs:

  • Folic acid can cause a more or less sensitive reduction in blood pressure . Therefore, to avoid such side effects, patients taking drugs or natural substances that lower blood pressure must scrupulously respect the doses of folic acid prescribed by the doctor.
  • Folic acid must be used with extreme caution in combination with aspirin : some studies performed in humans suggest that, in similar circumstances, vitamin B9 is able to reverse the beneficial effects of aspirin on C-reactive protein ( known inflammatory marker). Let us briefly recall that aspirin can be used in the treatment of diseases such as acute pericarditis or other cardiac pathologies to reduce blood levels of C-reactive protein (exaggerated by the disease); in similar circumstances, the concomitant use of folic acid and aspirin cancels or reverses the effect of the drug.
  • An intravenous loading dose of folic acid, vitamin B6 and vitamin B12, followed by oral intake of the same cocktail of substances, administered daily after a coronary stent operation (a small tube inserted into an artery to prevent it from clogging ) could increase the risk of restenosis (reformation of the atheromatous plaque that occurs in the first few months following surgery to dilate the artery). To minimize the risk of restenosis in these patients, administration of this vitamin combination should be avoided.
  • It appears that prophylactic and long – term supplementation of folic acid and iron may somewhat increase the risk of death in patients living in areas of high malaria risk . We briefly recall that folic acid can be used in the treatment of malaria anemia together with iron because the synergistic action of the two substances seems to significantly improve the anemic picture compared to monotherapy with iron alone. However, it seems that the long-term administration of drugs, for prophylactic purposes, is not recommended due to the increased risk of death.
  • Folic acid can reduce blood glucose levels : for this reason, diabetic patients taking specific drugs to control blood sugar must pay particular attention when taking folic acid to avoid unpleasant side effects.


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