Norepinephrine is a neurotransmitter and hormone produced by the adrenal glands and certain neurons in the brain. It plays a crucial role in the body's "fight or flight" response, helping to regulate blood pressure, heart rate, and blood sugar levels. Norepinephrine is involved in attention, focus, and mood regulation, making it important for cognitive functions. In the medical field, norepinephrine is often used as a medication to treat low blood pressure, particularly in critical care settings. It works by constricting blood vessels, which increases blood flow and improves circulation. Abnormal levels of norepinephrine can be associated with conditions like depression and anxiety disorders.