Folic acid: uses, pregnancy advice and cautions

Folic acid is the artificial version of folate, a B vitamin the body needs to make healthy red blood cells and for early development of an unborn baby. The NHS lists four uses: treating folate deficiency anaemia, supporting fetal development to prevent serious conditions such as spina bifida, preventing folate depletion during dialysis, and reducing the side effects of methotrexate.

It is available as tablets, as liquid solutions and in multivitamin combinations. Lexpec is one brand the NHS names.

The NHS recommends folic acid for the first 12 weeks of pregnancy, ideally beginning 3 months before conception. Some women need a higher dose than the standard recommendation, and that decision belongs to a doctor or midwife.

It can usually be taken while breastfeeding, but check with a pharmacist or doctor first.

Tell the prescriber or pharmacist if you have had an allergic reaction to folic acid, if you have vitamin B12 deficiency anaemia or pernicious anaemia, if you have coronary stents, or if you have cancer.

The NHS gives these as reasons to get advice before using it, so do not start it on your own if any apply to you.

Swallow tablets whole with a glass of water, and use the measuring device that comes with a liquid. The dose and length of treatment depend on the reason it was prescribed, so follow your prescriber and the leaflet rather than a general figure. If you miss a dose, take it as soon as you remember and then take the next dose at the usual time.

Because folic acid is also sold in multivitamin combinations, check the label of any other supplement you use so that you do not double up without realising, and mention all of them to the pharmacist or doctor who supplies your folic acid.

Common effects are bloating, wind, nausea and loss of appetite. The liquid may also cause diarrhoea, vomiting and a rash. Anaphylaxis is rare but needs emergency care, so call 999 for swelling of the lips, mouth or throat, difficulty breathing or collapse.

Suspected side effects can be reported to the MHRA through the Yellow Card scheme.

The NHS names epilepsy medicines (phenytoin, phenobarbital and primidone), the antibiotics chloramphenicol and co-trimoxazole, sulfasalazine, lithium and aspirin as medicines to mention before taking folic acid.

It is best to avoid or limit alcohol, because it can affect how well folic acid works.

People taking methotrexate are often prescribed folic acid alongside it to cut down side effects. How often you take it is set by your prescriber, so follow the instructions you were given for your own course.