Alpha 2-adrenergic agonist refers to a drug that reduces the activity of the neurotransmitter norepinephrine by stimulating certain receptors within the central nervous system (central presynaptic alpha 2-adrenergic receptors). The release of norepinephrine triggers action within the sympathetic nervous system. This part of the nervous system regulates certain involuntary activities during stress, such as increasing the heart rate, deepening breathing, and raising blood pressure. Norepinephrine also plays a role in regulating mood and emotion. The administration of Alpha 2-adrenergic agonists may result in a reduced heart rate and lowered blood pressure and have depressive or sedative effects.