Pseudoephedrine is a sympathomimetic (an agent that mimics stimulation of the sympathetic nervous system) that acts predominantly on the alpha receptors but has little or no effect on beta receptors. This allows pseudoephedrine to relieve nasal congestion with little or no central nervous system stimulation, which is why this drug has become so popular in over-the-counter cold remedies. Side effects include convulsions, hallucinations, irregular heartbeat and shortness of breath.