BI-409306 is a selective inhibitor of phosphodiesterase 9 (PDE9), an enzyme involved in the breakdown of cyclic guanosine monophosphate (cGMP) in the brain. By inhibiting PDE9, BI-409306 increases cGMP levels, which plays a role in synaptic plasticity, memory, and learning. This mechanism has made it a candidate for the treatment of cognitive impairments associated with neurological disorders, particularly schizophrenia. In clinical development, BI-409306 has been investigated as an adjunctive therapy to improve cognitive function in patients with schizophrenia who continue to experience cognitive deficits despite standard antipsychotic treatment. Its ability to target specific pathways involved in memory and cognition without directly affecting dopamine or serotonin receptors offers a novel approach to addressing unmet needs in psychiatric care. Research has also explored its potential in other conditions involving cognitive decline, though its primary focus remains in neuropsychiatric applications.