 These are sympatholytic drugs that block the effects of adrenergic alpha receptors while having little or no effect on beta receptors.Drugs belonging to this group can have very different effects, however, depending on whether they primarily block alpha-1 receptors, alpha-2 receptors, or both.Alpha-2 receptors, as described elsewhere in this article, are frequently located on norepinephrine-releasing neurons themselves and have inhibitory effects on them; consequently, blockage of alpha-2 receptors usually results in an increase in norepinephrine release.