1. A reference to inhibiting or being antagonistic to nerve impulses of the sympathetic nervous system.
2. Opposing the action of sympathetic postganglionic fibers and their adrenergic transmitters.
3. A blocking transmission of impulses transmitted by the postganglionic fibers of the sympathetic nervous system to effector organs or tissues, inhibiting such sympathetic functions as smooth muscle contraction and glandular secretion.

Postganglionic fibers are nerve fibers that pass to involuntary muscle and gland cells and have their cell bodies in the autonomic ganglia (aggregations of cell bodies of neurons of the autonomic nervous system; the parasympathetic and the sympathetic ganglia combined).