Is Folic Acid Bad for You? Safety, Doses and Interactions

For most people, folic acid is not harmful when taken in the amounts usually found in supplements. It is the synthetic form of vitamin B9, used for decades in supplements and fortified foods, and its safety has been assessed by expert panels. A review published in the Annals of the New York Academy of Sciences concluded that the body of evidence examined by two independent panels — the U.S. National Toxicology Program and the UK Scientific Advisory Committee on Nutrition — did not establish risks arising from the mandatory fortification programmes in place, although it stresses that more research is needed on supplement intake above the upper limit ¹.

That does not mean the question "is it bad for you?" has a single answer. There are three distinct situations that are often confused: normal supplement doses, doses far above the tolerable upper limit, and specific groups of people (for example, those with vitamin B12 deficiency or taking certain medicines). This article separates these scenarios and explains what the evidence shows in each one.

What is the difference between food folate and folic acid in supplements?

"Folate" is the general term for the group of vitamin B9 compounds that occur naturally in foods (pulses, green leafy vegetables, liver). "Folic acid" is the oxidised, monoglutamate form, used in supplements, fortified foods and medicines, with greater bioavailability than food folate ².

This difference in bioavailability matters for safety: because folic acid from supplements is better absorbed, it is easier to exceed the tolerable upper limit with supplements than with food alone. That is also why supplementation recommendations are expressed in micrograms of folic acid and not in dietary folate equivalents.

It is worth distinguishing three scenarios that are often confused. First, the usual dose of a supplement: it is safe for most people. Second, prolonged intake above the tolerable upper limit, which is the point at which symptoms such as stomach pain, nausea or sleep changes begin to appear — not acute poisoning, but an excess maintained over weeks or months. Third, individual situations (B12 deficiency, epilepsy, methotrexate) where the decision to supplement requires professional assessment. A truly dangerous dose is rare and is usually associated with medication errors or products with concentrations far above the recommended amount, not with supplements taken according to the label.

What does the evidence say about the safety of folic acid?

The review by Field and Stover is the most direct reference for this question. The author describes "a large body of literature" demonstrating the effectiveness of maternal folic acid in preventing neural tube defects and concludes that the available evidence has not established risks associated with the exposure levels currently used in fortification programmes ¹.

An earlier review, published in the European Journal of Clinical Nutrition, is more cautious: the authors note that, although folate is considered non-toxic, the potential adverse effects of excessive folic acid intake have not been well communicated to those taking supplements, and that the available studies show discrepant results ³. In other words, the uncertainty is not in normal doses, but in prolonged intake above the upper limit.

Who is most at risk of folate deficiency (and therefore benefits from supplementation)

Before discussing risks, it is worth remembering that folate deficiency is common. A review published in the European Journal of Clinical Nutrition refers to studies pointing to deficiency prevalences as high as 85.5% in women aged 16 to 49 in the United Kingdom ³. This does not mean that almost all of these women need supplements, but it shows that concern about excess should not overshadow concern about deficiency.

A general review on micronutrients identifies the groups at greatest risk of deficiencies: older adults, pregnant women, people with alcohol use disorder, people on vegetarian or vegan diets and people with medical conditions or long-term medication that alters the absorption, metabolism or excretion of nutrients. In these groups, micronutrient supplementation can be useful — but doses above the recommended amounts can cause adverse effects ⁴.

The case of pregnancy: where the evidence is strongest

The randomised clinical trial by the Medical Research Council, published in the Lancet in 1991, is a landmark in this area. The study randomised 1,817 women at high risk of having a pregnancy affected by a neural tube defect (because they had had a previously affected pregnancy); of the 1,195 who had a completed pregnancy with a known outcome, folic acid supplementation reduced the risk by 72%, with no demonstrated harm — although the authors acknowledge that the study had little power to detect rare or mild adverse effects ⁵.

A more recent systematic review, published in Medicine, reinforces that folic acid is critical in rapidly proliferating tissues, such as the fetus, and that supplementation is particularly important before conception and in the first trimester, when neural tube closure occurs ⁶. If you are pregnant, breastfeeding or planning to become pregnant, the dose should be the one your doctor advises — not the one you find in an article or on a label.

When folic acid needs more care

There are situations in which folic acid supplementation is not a neutral decision. Not because the vitamin is toxic, but because it can interact with health problems or with medicines.

Undiagnosed vitamin B12 deficiency

Folic acid can correct the anaemia caused by vitamin B12 deficiency without treating the neurological damage associated with that deficiency. That is why, in people at risk of B12 deficiency — for example, those following an unsupplemented vegan diet — assessment should be carried out before supplementing folic acid on its own. A 2024 meta-analysis on the functional vitamin B12 status of adult vegans showed significantly lower serum B12 values and higher total homocysteine in this group, and analysed the effect of B12 supplement use ⁷. If you have doubts about your B12 status, see how vitamin B12 works.

Antiepileptic medicines

The interaction between phenytoin and folic acid is well documented. A review published in the Annals of Pharmacotherapy describes a bidirectional relationship: phenytoin reduces serum folate levels, and folic acid supplementation in patients with epilepsy and folate deficiency alters the pharmacokinetics of phenytoin, generally lowering serum concentrations of the drug and potentially leading to loss of seizure control ⁸. Anyone taking antiepileptics should talk to their neurologist before supplementing.

Methotrexate

Methotrexate is a folate antagonist, used in rheumatic diseases and in some cancer treatments. In a clinical setting, folic acid is often co-administered to reduce the toxicity of methotrexate, but the optimal dose is not established. An exploratory randomised clinical trial, published in Clinical Rheumatology, compared 10 mg versus 5 mg of folic acid per week for 12 weeks in 44 patients with rheumatic diseases on stable methotrexate (42 completed the study): there were no significant differences in liver injury or in most outcomes at 84 days ⁹. This is a specific medical context — never adjust or start folic acid on your own if you take methotrexate.

What the research does not show: folic acid and cardiovascular disease

A common idea is that folic acid, by lowering homocysteine, protects the heart. The evidence does not support that expectation in the general population. A meta-analysis of 16 placebo-controlled trials, with 44,841 participants, found no effect of folic acid supplementation on major cardiovascular events, stroke, myocardial infarction or death from any cause ¹⁰.

In people with kidney disease, a meta-analysis of 11 trials also showed no clear cardiovascular benefit from lowering homocysteine with folic acid ¹¹. And in a randomised trial with 20,702 Chinese adults with hypertension, the combination of enalapril and folic acid significantly reduced the risk of a first stroke compared with enalapril alone ¹² — but this is a specific population, with an intervention combined with an antihypertensive, and not an isolated effect of the supplement. Do not extrapolate these results to taking folic acid for cardiovascular prevention.

Doses: what the studies say and what the label says

The doses used in research vary widely and are not instructions for taking it. The MRC trial used folic acid supplementation around conception ⁵; the trial in rheumatic diseases compared 5 and 10 mg per week ⁹; the Chinese trial used 0.8 mg per day in combination with enalapril ¹². These values serve to describe what was studied, not to guide your intake.

If you are looking for a TuttiBear product with folic acid, the labels are clear about the dose per serving:

Product	Serving	Folic acid per serving
Hair & Nails Gummies	2 gummies	442 µg (221% NRV)
Appetite Control Gummies	2 gummies	400 µg (200% NRV)
Multivitamin Gummies	2 gummies	10 µg of folic acid
Kids' Multivitamin Gummies (+2 years)	1 gummy	115 µg of folate (58% NRV)

Note that the Kids' Multivitamin Gummies are intended for children from 2 years of age, under adult supervision, and that the indicated dose is 1 gummy per day — it is not a dose for adults. To better understand how to interpret these values, see folic acid daily dose.

In any case, the label dose is the one to follow. Do not increase your intake on your own based on study doses.

For reference, the tolerable upper limit of folic acid in the synthetic form, set by EFSA for adults, is 1,000 µg per day ¹³. Hair & Nails Gummies (442 µg per 2-gummy serving) and Appetite Control Gummies (400 µg per 2-gummy serving) stay below that value when taken according to the label, but it is worth taking into account the folic acid that may come from other supplements or fortified foods on the same day.

Common side effects and warning signs

When symptoms occur with folic acid, they are usually mild and gastrointestinal. A review published in the European Journal of Clinical Nutrition notes that the adverse effects of excessive intake have not been well communicated to those taking supplements ³ — which reinforces the importance of reading the label and not exceeding the recommended daily dose.

Signs that justify stopping and seeking professional advice:

• New neurological symptoms — tingling, numbness, changes in memory or coordination. They may indicate B12 deficiency masked by folic acid.
• Allergic reactions — itching, rash, swelling of the face or difficulty breathing. They are rare, but require immediate medical assessment.
• Persistent gastrointestinal discomfort that does not improve with a lower dose or with taking it after a meal.

If you are pregnant, breastfeeding, have a diagnosed condition or take chronic medication, talk to a healthcare professional before starting any supplement.

If you are pregnant, breastfeeding, have a diagnosed condition or take chronic medication, talk to a healthcare professional before starting any supplement.

Gummies or tablets: does anything change for safety?

The active substance is the same, so the precautions regarding dose and interactions apply equally. Gummies do, however, have practical particularities: they contain polyols (such as maltitol), whose excessive consumption may have a laxative effect, and their sweet appearance makes accidental consumption by children more likely. Keep supplements out of reach of little ones and, in case of excessive intake, contact a doctor, pharmacist or poison information centre. For a more detailed comparison, see folic acid gummies vs tablets.

If you have diabetes, insulin resistance or are managing your weight, check the label and count the carbohydrates in the gummies. Sugar and polyols can also contribute to tooth decay, so it is best to brush your teeth after eating them, rather than taking them throughout the day as if they were sweets.

What is still unclear

The review by Field and Stover is explicit: more research is needed to assess the health effects of folic acid supplement use when the currently defined upper limit is exceeded ¹. A review published in the European Journal of Clinical Nutrition adds that the results of studies on high intake are discrepant, which creates confusion about the advisability of mandatory fortification programmes in other countries ³.

It is also not fully established whether synthetic folic acid and natural folate have identical long-term effects; a 2024 narrative review on neural tube defect prevention notes that clinical studies assessing the efficacy of 5-MTHF (the active form) in a way comparable to folic acid are still lacking ².

In summary

Folic acid is not harmful to most people at the doses usually found in supplements, and the safety evidence at the exposure levels currently used in fortification programmes is reassuring, although more research is needed on intake above the upper limit ¹. What needs attention is prolonged intake above the upper limit, undiagnosed B12 deficiency, taking antiepileptics such as phenytoin ⁸ and methotrexate ⁹. If you have a health condition, take medication or are pregnant, talk to a healthcare professional before supplementing. And always follow the label dose — not the dose from a study.

Frequently asked questions

Is folic acid bad for your liver?

There is no evidence that folic acid causes liver damage in healthy people taking normal supplement doses. In a clinical trial in patients with rheumatic diseases taking methotrexate, comparing 5 mg with 10 mg of folic acid per week for 12 weeks showed no significant differences in liver injury. If you have liver disease, talk to your doctor before supplementing.

Can I take folic acid every day?

Yes, most people can take folic acid daily within the doses stated on the label. Daily supplementation is common practice and the safety evidence at current exposure levels is reassuring. What you should avoid is exceeding the tolerable upper limit over the long term, and in that case guidance from a healthcare professional is essential.

Can folic acid mask a vitamin B12 deficiency?

Yes, and it is one of the best-documented concerns. Folic acid can correct the anaemia caused by B12 deficiency without treating the neurological damage associated with that deficiency, which can delay diagnosis. If you are at risk of B12 deficiency — for example, if you follow a vegan diet without supplementation — ask for an assessment before taking folic acid on its own.

Can people taking methotrexate take folic acid?

Folic acid is often co-administered with methotrexate in a clinical setting to reduce the toxicity of the medicine, but the optimal dose is not established and the decision is always medical. Never start, change or stop folic acid on your own if you take methotrexate. Talk to the doctor who prescribes your treatment.

Does folic acid make you gain weight?

There is no evidence that folic acid causes weight gain. B-complex vitamins take part in energy metabolism, but that does not translate into weight changes. If you have noticed weight changes since starting a supplement, other factors — diet, physical activity, medication — are more likely.

What is the dose of folic acid in TuttiBear gummies?

It depends on the product. Hair & Nails Gummies provide 442 µg of folic acid per 2-gummy serving (221% NRV) and Appetite Control Gummies provide 400 µg per 2-gummy serving (200% NRV). Multivitamin Gummies state 10 µg of folic acid per 2-gummy serving. Always follow the label dose and do not exceed the recommended daily dose.