Brain-derived neurotrophic factor (BDNF) is a key neurotrophic factor in the brain. It plays an important role in the etiopathogenesis and pharmacotherapy of mental disorders, such as depression or schizophrenia. In recent years, studies have shown that cognitive processes, which are impaired in the course of mental disorders, significantly change BDNF levels in the brain. Administered to rats at a dose of 20 mg/kg (b.d. for 5 weeks), venlafaxine (VEN) increases BDNF levels in the hippocampus and cortex, compared to controls. Administered at a dose of 0.5 mg/kg (b.d. for 5 weeks), olanzapine (OLA) significantly increases BDNF levels in both the cortex and the hippocampus. Similarly, nicotine (NIC) administered at a dose of 0.2 mg/kg (b.d. for 5 weeks) increases BDNF concentrations in both the hippocampus and the cortex. Combined administration of NIC with VEN or OLA does not increase BDNF levels in the hippocampus or the cortex. Based on our study, it can be claimed that BDNF mediates behavioral responses only to drugs used individually and participates in the antidepressant and procognitive effects of the study compounds. BDNF also initiates plastic changes and modulation of synaptic activity in rat brains.