The pseudoephedrine contained in many

The pseudoephedrine contained in many "non-drowsy" drugs like these is really an amphetamine in disguise, differing from methamphetamine by only one oxygen atom, a proton and a symmetry operation. These differences are sufficient, however, for the stimulant effects to be hindered by the passage of pseudoephedrine molecules across the blood-brain membrane, plus orders of magnitude difference in its activity where it counts - the dopamine neurons.
So that's where the "pseudo" comes from.
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