Neuropeptide Y (NPY) is a 36-aa neuropeptide that acts as a neurotransmitter in the brain and in the autonomic nervous system of humans. In the autonomic system, NPY is produced mainly by neurons of the sympathic nervous system and serves as a strong vasoconstrictor and also causes growth of fat tissue. In the brain, NPY is produced in various locations including the hypothalamus. NPY has several functions: increasing food intake and storage of energy as fat, reducing anxiety and stress, reducing pain perception, affecting circadian rhythm, reducing voluntary alcohol intake, lowering blood pressure, and controling epileptic seizures. NPY has been studied for its role in obesity by interacting with the leptin receptor and neuropeptide Y receptors (Y1 and Y2).