Final answer:
Indirect sympathomimetics mimic norepinephrine or increase its production and release from postganglionic fibers. They enhance the effects of adrenergic chemicals by blocking neurotransmitter reuptake or removal from the synapse.
Step-by-step explanation:
Indirect sympathomimetics are drugs that either mimic norepinephrine at the synapses between sympathetic postganglionic fibers and their targets or increase the production and release of norepinephrine from postganglionic fibers. These drugs enhance the effects of adrenergic chemicals released from the fibers by blocking the removal or reuptake of the neurotransmitter from the synapse.