Butterbur (Petasites hybridus) has been studied for its effects on allergic rhinitis (hay fever). Several randomized controlled trials and systematic reviews have investigated its efficacy. The active compounds in butterbur, particularly petasin and isopetasin, are thought to have anti-inflammatory and antihistamine-like effects, which may counteract the symptoms of allergic rhinitis.

Notably, a placebo-controlled study published in the British Medical Journal (2002) found that butterbur extract was as effective as cetirizine, a standard antihistamine, in reducing symptoms of hay fever, without causing drowsiness. Other studies and meta-analyses have supported these findings, though some have noted variations in the quality and standardization of butterbur preparations.

Major guidelines, such as those from the American Academy of Allergy, Asthma & Immunology (AAAAI), mention butterbur as an option with some supportive evidence, though they highlight the importance of using products free of pyrrolizidine alkaloids (PAs), which are toxic. Overall, while evidence is not as robust as for conventional antihistamines, there is moderate scientific support (score: 3/5) for the use of butterbur in managing allergic rhinitis symptoms.