The prime function of the adrenergic or sympathetic nervous system is to help the human being to adjust to stress and prepare the body for fight or flight reactions. Neurotransmitters of the sympathetic system are noradrenaline and dopamine. Adrenaline is the major hormone secreted by the adrenal medulla. Adrenergic receptors are of two types’ namely–alpha and beta. Stimulation of alpha receptors mainly produces excitatory effects while beta stimulation causes mainly inhibitory effects. Both alpha and beta adrenergic receptors are G-protein coupled receptors.