A composition and method of treating adrenergic dysregulation by administering the composition is disclosed, wherein the composition comprises a .alpha..sub.2-adrenergic receptor agonist; a pharmaceutically acceptable hydrophilic matrix and a release-retardant of a metal alkyl sulfate. In embodiments, the composition provides a sustained release of the agonist, wherein after administration of the composition no more than once about every 12 hours to a subject having a steady state plasma concentration of the .alpha..sub.2-adrenergic receptor agonist, the agonist's plasma concentration peak-to-trough ratio is no greater than about 1.9.