 These are 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 . <unk> , for example , is used for the treatment of anxiety disorders and insomnia , and also as a sedative <unk> for patients about to undergo surgery . <unk> , another drug in this group , is also a powerful sedative and is often used in combination with ketamine as a general anaesthetic for veterinary surgery — in the United States it has not been approved for use in humans . 
