The occupancy-driven pharmacology model in psychopharmacology has guided drug discovery and development for decades, whereby the goal is stable receptor occupancy over an extended period with a direct relationship of drug exposure to pharmacodynamic and therapeutic response. Event-driven pharmacology (EDP) is a concept where the acute pharmacodynamic actions of a plastogen, a transient binding event, drive changes resulting in sustained pharmacodynamic effects that greatly outlast the time frame of drug exposure. Such plastogens may be neuroplastogens producing a measurable change in neuroplasticity without inducing subjective mental states or psychoplastogens exerting neuroplastic effects in addition to causing dissociation, hallucinations, or psychotomimetic symptoms. Within neuropsychiatry, plastogens have been shown to induce long-lasting neural plasticity and persistently activate synaptic machinery that primes synapses to respond to subsequent stimuli (metaplasticity), often following either a single dose or repeated administration of intermittent doses. Developing rapid-acting plastogens to adhere to a traditional target occupancy dose optimization model that achieves consistent drug target occupancy over an extended period of time may paradoxically exert few or no durable benefits while increasing side effect burden. We review evidence supporting the concept that plastogens, including the rapid-acting antidepressant ketamine and classical psychedelics, operate within the EDP model. With the emergence of EDP, new methods for drug development, clinical dosing, and biomarker adoption will need to be developed to account for distinctive pharmacological actions. Rapid-onset plastogens, rationally administered, have profound potential in the treatment of depression and many other neurological and psychiatric diseases characterized by synaptic dysfunction.
