Butterbur is not universally safe, and its safety depends heavily on the specific product you use. The plant naturally contains toxic compounds that can cause serious liver damage, including liver failure. Specially processed extracts that remove these toxins have been used in clinical trials with relatively few side effects, but even some products labeled as toxin-free have been linked to liver injury.
The Liver Toxicity Problem
Raw butterbur contains pyrrolizidine alkaloids, a class of naturally occurring toxins found in the plant’s leaves, stems, and roots. These compounds can damage the tiny blood vessels inside the liver, causing a condition called sinusoidal obstruction syndrome, where blood flow through the liver gets blocked. Over time, this leads to serious liver injury.
The safety record is concerning. Globally, 40 cases of liver toxicity linked to butterbur have been documented, including nine cases of acute hepatitis and two cases of liver failure severe enough to require a transplant. Some of these cases occurred in people using products that were reportedly free of pyrrolizidine alkaloids, which raises questions about quality control across the supplement industry. The NIH’s National Center for Complementary and Integrative Health has specifically flagged this issue.
Why Neurologists Pulled Their Recommendation
In 2012, the American Academy of Neurology issued a guideline calling butterbur a treatment with “established efficacy” for preventing migraines. That recommendation was formally retired in 2015. The AAN’s board of directors withdrew the entire guideline, stating that its conclusions were “no longer valid and no longer supported” due to serious safety concerns. The issue was never about whether butterbur works for migraines. It was about whether the liver risks were acceptable.
This is unusual. Medical societies rarely pull an entire guideline over a single treatment. The move reflected growing unease about the gap between butterbur’s performance in controlled trials and the real-world difficulty of guaranteeing a safe product on store shelves.
PA-Free Extracts: Safer but Not Risk-Free
Commercially available butterbur supplements are typically processed to remove pyrrolizidine alkaloids, and these products are marketed as “PA-free.” The most studied brand, Petadolex, uses a proprietary extraction method and has been the formulation used in most clinical trials. At standard doses (50 to 150 mg per day, standardized to contain about 7.5 mg of the active compounds called petasins per dose), side effects in trials were generally mild: digestive discomfort, burping, and fatigue were the most commonly reported.
The catch is that “PA-free” on a label doesn’t guarantee zero risk. Supplement manufacturing isn’t held to the same standards as pharmaceutical production in most countries, and independent testing has found inconsistencies between what’s on the label and what’s in the bottle. The rare liver injury cases linked to supposedly PA-free products suggest that either trace amounts of the toxins remained, or butterbur may cause a different type of liver reaction in some people. Researchers reviewing these cases noted that the pattern of injury looked more like an unpredictable immune-mediated reaction than the direct toxic damage pyrrolizidine alkaloids typically cause.
Drug Interactions
Butterbur’s active compounds can affect how your liver processes other medications. Specifically, they interact with a key enzyme (CYP3A4) that breaks down a wide range of drugs. The reassuring finding from laboratory studies is that this interaction only becomes significant at concentrations far higher than what you’d reach at normal doses, more than 65 times the level found in your blood after a standard dose.
Researchers also tested butterbur alongside common migraine medications, including ibuprofen, acetaminophen, and naratriptan. At normal doses of both butterbur and these drugs, no signs of liver stress appeared in human liver cell cultures. Problems only showed up when butterbur concentrations were pushed to more than 49 times the normal blood level. In practical terms, standard doses of butterbur are unlikely to cause dangerous interactions with common pain relievers, but the picture is less clear for people taking multiple medications metabolized through the same liver pathway.
Who Should Avoid Butterbur
Butterbur belongs to the Asteraceae plant family, the same family as ragweed, daisies, and marigolds. If you have allergies to any of these plants, you may react to butterbur as well due to cross-reactive proteins.
There is essentially no safety data on butterbur use during pregnancy or breastfeeding. Given the liver toxicity concerns and the lack of clinical evidence in these populations, most health authorities consider it inappropriate for pregnant or nursing women. People with existing liver disease should also avoid it, since any additional stress on compromised liver function raises the stakes considerably.
What This Means in Practice
Butterbur sits in an uncomfortable middle ground. Clinical trials show it can reduce migraine frequency and ease seasonal allergy symptoms. But the liver safety signal is real, the supplement market is poorly regulated, and the one major medical society that endorsed it took that endorsement back. If you do choose to use butterbur, the lowest-risk approach is to use only PA-certified extracts from manufacturers that provide third-party testing, stick to studied dosages (typically 50 to 75 mg twice daily for migraines), and get liver function monitored periodically. Many neurologists have shifted toward recommending other preventive options that don’t carry the same liver concerns.