Butterbur for migraine and hay fever: benefit versus liver risk

Butterbur has been used for centuries; medieval Europeans burned its roots in the belief that the smoke would fight plague. Its modern appeal rests on two sets of studies. Root extracts were tested for preventing migraine in adults and children, and leaf extracts were tested for allergic rhinitis, the symptoms most people call hay fever.

NIH summarises that a root extract may reduce migraine frequency when taken by mouth, and that studies of a leaf extract suggest it may help allergic rhinitis. Little research exists on any other use, so no conclusions can be drawn for other conditions.

Pyrrolizidine alkaloids are plant defence chemicals produced by several families of plants, including those in the butterbur genus. In the body they can injure liver cells and the small veins of the liver and, with prolonged exposure, may contribute to cancer. NIH therefore advises that only butterbur products processed to remove PAs and labelled or certified as PA-free should even be considered.

The MHRA has gone further for the UK. In its Drug Safety Update it describes butterbur as containing PAs that can cause serious adverse effects such as liver damage and organ failure, says it has published a safety alert advising consumers not to take unlicensed butterbur herbal remedies, and states the advice remains unchanged. The same article credits Yellow Card reporting and vigilance for identifying the concern.

• Products containing PAs should not be used in pregnancy or while breastfeeding because they may cause birth defects or liver damage.

• PAs may be absorbed through broken skin, so PA-containing products may not be safe on cuts or scrapes.

• Little is known about whether PA-free butterbur is safe in pregnancy or breastfeeding.

Several studies, including some in children and adolescents, have reported that PA-free butterbur appears safe by mouth for up to 16 weeks. That is a short window, and migraine prevention is usually considered over months. NIH also records rare cases of liver injury linked to products that were reported to be PA-free, which suggests that labels or processing are not always reliable, or that other mechanisms are involved.

Common side effects of oral butterbur include belching, diarrhoea, drowsiness, rash and stomach upset. People allergic to related plants such as ragweed, chrysanthemums, marigolds and daisies may react to butterbur as well.

The American Academy of Neurology recommended butterbur for migraine prevention in 2012 and stopped doing so in 2015 because of serious safety concerns. That reversal is the most important single fact on this page: a body that had looked at the same trials concluded that the possible benefit no longer justified the possible liver harm.

UK practice for migraine prevention relies on better-characterised options through a GP or neurologist. Someone who has been taking butterbur should not simply stop worrying: if they have had unexplained tiredness, nausea, dark urine, pale stools, yellowing of the skin or eyes, or upper abdominal pain while using it, a GP can arrange blood tests of liver function.

Unlicensed herbal remedies sold online or in shops are not assessed by the MHRA in the way registered products are. The NHS advises people not to buy unlicensed herbal medicines online and to look for a traditional herbal registration mark and product code. The MHRA's guidance for patients is to check for a THR number or a product licence number on the label.

Given the MHRA's explicit warning on unlicensed butterbur, a supplement-shelf product with no registration is the situation the warning is aimed at. Report any suspected reaction through the Yellow Card scheme with the brand, ingredients and manufacturer details.