Histamine is best known as the chemical that makes your eyes water and your nose run during allergy season. But a new study from the University of Oxford suggests it plays an unexpected and fundamental role in human memory — and that a drug which raises histamine levels in the brain can improve how well we remember.
The drug is pitolisant (brand name Wakix), an H₃ receptor inverse agonist that is already approved for treating narcolepsy. It works by removing a natural brake on histamine release in the brain. In a randomized, double-blind, placebo-controlled trial of 60 healthy volunteers, a single dose of pitolisant improved memory accuracy by approximately 11 percent.
“We think it’s changing something called novelty-linked arousal,” said Michael Colwell, the study’s lead author at Oxford’s Department of Psychiatry. “So, how alert we feel when we see new things in the environment.”
The histamine-memory pathway
Histamine-producing neurons are clustered in a tiny region at the base of the brain called the tuberomammillary nucleus. From there, their fibers project directly into the hippocampus — the brain’s primary memory center. The Oxford team used functional MRI to show that pitolisant strengthened the connectivity between the tuberomammillary nucleus and the hippocampus, and that a machine-learning classifier could distinguish pitolisant-treated brains from placebo-treated ones with 88.5 percent accuracy based on this connectivity pattern alone.
“They are densely packed around areas of the brain which are involved in learning and memory,” Colwell said of histamine receptors.
The drug affected multiple memory systems. Episodic memory retrieval improved by approximately 11 percent. Working memory under high cognitive load showed an adaptive shift in strategy — the brain allocated neural resources more efficiently. Reinforcement learning from negative outcomes became more stable. And during rest periods after learning, temporal-hippocampal connectivity was strengthened, consistent with enhanced offline memory consolidation.
The antihistamine connection
The finding has a direct implication for the millions of people who take antihistamines. Older, first-generation antihistamines — such as diphenhydramine (Benadryl) — cross the blood-brain barrier and block histamine’s effects, which may explain the “brain fog” and memory impairment long associated with these drugs.
“A lot of those older ones got into the brain. They would have made people less able to remember things, which you often see when people were taking those antihistamines for a long time,” Colwell said.
Modern second-generation antihistamines (cetirizine, loratadine, fexofenadine) are designed to stay out of the brain, so they should not impair memory — a design improvement that the study’s findings validate.
Caveats and context
The study, published in Nature Communications (DOI: 10.1038/s41467-026-73865-9), is the first human causal demonstration of histamine’s role in learning and memory — translating decades of animal research into humans. The research was led by Colwell, Catherine Harmer, and Susannah Murphy at Oxford, with collaborators at the University of Edinburgh.
The authors caution that pitolisant is not a “smart drug” for healthy people. It disrupts sleep, which harms long-term memory, and its effect in healthy volunteers was described as normalizing rather than supercharging cognitive function. Holger Stark of Heinrich Heine University, commenting on the research, noted: “A recurring finding has been that pitolisant can help restore impaired cognitive function and improve attention when these are compromised by disease. In most cases, however, the effect has been to normalise impaired function rather than to enhance cognition beyond normal levels.”
The study raises the question of whether other drugs targeting the histamine system could be developed for memory disorders without the sleep side effects. For now, the headline finding is clear: histamine, long dismissed as merely an allergy mediator, is a key player in how the brain learns and remembers.
Sources
1. New Scientist, “The allergy culprit histamine also boosts our memory” (8 July 2026). https://www.newscientist.com/article/2533166-the-allergy-culprit-histamine-also-boosts-our-memory/
2. Colwell, M.J. et al., “Histamine shapes the neurocomputational dynamics of human learning”, Nature Communications (2026). DOI: 10.1038/s41467-026-73865-9