Cortisol

Cortisol is a steroid hormone released by the adrenal glands that regulates metabolism, immune function and the body's response to stress in dogs, cats and people.

Its release is governed by the hypothalamic-pituitary-adrenal axis and follows a daily rhythm, rising in response to challenges such as unfamiliar environments, loud noises, travel or separation. In dogs it can be measured in blood, saliva, urine and hair, with saliva popular in behavior research because sampling is less stressful and reflects recent minutes rather than days. Abnormally high or low baseline levels also signal endocrine diseases such as Cushing's or Addison's disease, which veterinarians diagnose with specific stimulation and suppression tests.

As a stress marker, cortisol has limits: levels vary with time of day, exercise, food and handling, and a change in cortisol alone does not prove an animal feels calmer. Some canine cannabidiol studies have reported lower cortisol responses to a stressor, findings that must be read alongside behavior and heart-rate data rather than as proof of a calming effect.