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Ciproxifan never had a pharma sponsor chasing an indication; it exists almost entirely as an academic tool compound, and it became the reference histamine H3 antagonist that an entire generation of sleep, attention, and Alzheimer's-related rodent studies were built around. Its defining quirk is species selectivity: it binds rodent H3 receptors in the subnanomolar range but only moderately at the human receptor, which is exactly why it stayed a lab reagent instead of becoming a clinical candidate. Later work found it also reversibly inhibits monoamine oxidase A and B, an unplanned second mechanism that complicates interpreting some of the older behavioral data attributed purely to H3 blockade.
- improves wakefulness and attention in rodent models via H3 blockade
- increases hippocampal and cortical acetylcholine, noradrenaline, and dopamine release in rodents
- widely used reference compound for validating newer H3-targeted candidates
- reversible MAO-A/B inhibition adds a secondary monoaminergic effect in some assays
- Ciproxifan binds the rat and mouse H3 receptor far more tightly than the human one, a species gap that is the entire reason it stayed a lab reagent instead of a drug candidate.
Mechanism
H3 receptor /inverse with high affinity at rodent H3 (Ki roughly 0.4-6 nM) but only moderate affinity at human H3 (Ki roughly 46-180 nM); blocking H3 autoreceptors increases histamine, , noradrenaline, and release; also reversibly inhibits monoamine oxidase A and B at micromolar concentrations.
Safetyrisks and cautions, not medical advice
Ciproxifan has never been given to a person in any published study, which makes its risk in people not low but unmeasured; treat any claim to the contrary as unsupported. What stopped it short of the clinic was pharmacology rather than toxicology, since it binds the rat H3 receptor far more tightly than the human one and no sensible human dose could be read off the animal data. It also inhibits monoamine oxidase A and B reversibly at higher concentrations, which in a person would raise the usual MAO inhibitor worries about tyramine and serotonergic drugs.
History
Characterized through the late 1990s as part of the wave of nonimidazole H3 ligands that followed early H3 pharmacology work; never advanced toward clinical development because of its weak affinity at the human receptor, and instead became a standard reference tool in rodent studies of ADHD, Alzheimer's-related cognition, and wakefulness.
Subjective profileweighing the evidence above
A rodent-brain workhorse that was never built to be a human drug, and never tried to be one.
Resources
This entry is here for reference.
Research
- 1.Neurochemical and behavioral effects of ciproxifan, a potent histamine H3-receptor antagonist
- 2.Ciproxifan, a histamine H3 receptor antagonist, reversibly inhibits monoamine oxidase A and B
2 listed here; entry last updated August 2026
Reviews
My notesprivate to this device
FAQ
Was ciproxifan ever tested in people?
No. Its affinity at the human H3 receptor is far weaker than at the rodent receptor, so it stayed a laboratory tool rather than moving into clinical development.
What is ciproxifan actually used for today?
It is still widely used in academic labs as the standard reference H3 antagonist for rodent studies of attention, wakefulness, and Alzheimer's-related cognitive models.
Limitations of the evidence
- its weak human-receptor affinity means rodent findings do not translate directly
- unintended MAO inhibition complicates interpretation of some older behavioral studies
Notes and cautions
- no human dosing data exists; it was never advanced past animal studies