Adjunctive Huperzine A for owner‐directed aggression associated with hypersensitivity–hyperactivity syndrome in a dog: a case report

A 7‐month‐old female Golden Retriever was referred for owner‐directed aggression occurring during intense emotional arousal and characterised by a limited ability to down‐regulate arousal and inhibit impulsive motor patterns. Episodes were most frequently triggered by restraint or physical contact (including during vehicle entry/exit) and by attempts to remove acquired objects and had resulted in grade‐3 bites per the Dunbar bite scale. Clinical assessment was consistent with hypersensitivity–hyperactivity syndrome (HSHA), an ADHD‐like neurodevelopmental condition described in dogs and associated with hyperactivity, impulsivity and reduced behavioural inhibition. A multimodal treatment plan including environmental management and structured behaviour modification was implemented. Fluoxetine was initiated at approximately 0.9 mg/kg/day and was associated with a marked reduction in aggressive incidents and improved arousal regulation. A subsequent attempt to increase the fluoxetine dose to improve residual impulsivity resulted in a 50% reduction of appetite (approximately), necessitating a return to the prior dose. Huperzine A, a Chinese club moss alkaloid and centrally acting acetylcholinesterase inhibitor with additional neuroprotective effects, was then added at 200 μg orally every 12 h. Following adjunctive huperzine A, the dog showed further improvement in behavioural inhibition and impulse control with additional reductions in arousal‐linked impulsive behaviour and aggression and no reported adverse effects. This case highlights HSHA‐associated owner‐directed aggression and suggests that adjunctive huperzine A may be a useful option when dose‐limiting adverse effects prevent optimisation of SSRI therapy.