 These are sympathomimetic drugs that activate alpha-2 receptors or enhance their effects.Because alpha-2 receptors are inhibitory and many are located presynaptically on norepinephrine-releasing cells, the net effect of these drugs is usually to reduce the amount of norepinephrine released.Drugs in this group that are capable of entering the brain often have strong sedating effects, due to their inhibitory effects on the locus coeruleus.