BDNF

Brain-derived neurotrophic factor (BDNF) is a protein belonging to the neurotrophin family — a class of molecules that regulate the survival, growth, and maintenance of neurons. It is produced throughout the brain but is especially concentrated in regions tied to learning, memory, and mood regulation, including the hippocampus and prefrontal cortex.

A prominent theory in psychiatry, the neurotrophic hypothesis of depression, proposes that chronically low BDNF — driven by prolonged stress — contributes to the loss of synaptic connections seen in depressive illness. This framing has become central to how researchers understand both the condition and many of the treatments aimed at it.

How it works · its role

BDNF acts primarily by binding to the TrkB receptor (tropomyosin receptor kinase B) on the surface of neurons. This triggers intracellular signalling cascades that promote neuronal survival, the branching of dendrites, and the formation and consolidation of new synaptic connections.

A key downstream effect is the facilitation of long-term potentiation — a cellular process widely considered to be the basis of learning and memory. BDNF also regulates proteins that govern synapse structure. The result is a molecule that shapes not just which neurons survive, but how efficiently they communicate over time.

Relevance to substances & effects

Several substance classes modulate BDNF as part of their proposed mechanism of action. SSRIs and other classical antidepressants gradually increase BDNF expression in the hippocampus over weeks of use — a time course that mirrors the delayed onset of their clinical benefit, suggesting the two are meaningfully linked.

Ketamine and its relative esketamine produce rapid increases in BDNF signalling, which is thought to contribute to their fast-onset antidepressant effects — a property that distinguishes them sharply from conventional antidepressants.

Classic psychedelics such as psilocybin and LSD are associated with upregulation of BDNF and related plasticity pathways. Some researchers describe these compounds as psychoplastogens — substances that promote structural neuroplasticity quickly and durably. This observation has attracted considerable interest in the context of their studied effects on depression and post-traumatic stress.

Chronic heavy alcohol use and long-term opioid exposure are associated with dysregulation of BDNF signalling, particularly in reward circuits. This is thought to contribute to the blunting of plasticity that accompanies dependence, and to some of the cognitive and emotional difficulties that persist into early recovery.