Cortisol and depression

Cortisol is the body's main stress hormone, produced by the adrenal glands in response to activation of the hypothalamic-pituitary-adrenal (HPA) axis. In depression, this axis is often overactive — resulting in chronically elevated cortisol levels.

Chronically high cortisol has neurobiological consequences: it reduces neuroplasticity (the brain's ability to form new connections), can damage neurons in the hippocampus (a region critical for memory and emotional regulation), and disrupts sleep and other hormonal systems. This helps explain some of the cognitive symptoms of depression: difficulty concentrating, impaired memory, and a sense of "brain fog."

The cycle of stress → depression → elevated cortisol → more symptoms is one mechanism by which stressful events can trigger and sustain depressive episodes. Effective treatments for depression (antidepressants, psychotherapy) tend to normalize the HPA axis over time — one of the biological markers of recovery.