Decongestant

Pseudoephedrine is the defining molecule of the oral-decongestant category.

The alternatives are topical agents and oral phenylephrine, whose monograph-dose efficacy failed meta-analysis and which the FDA has proposed to remove from the OTC monograph as ineffective ^{3,4Reference 3Hatton RC et al. · 2007Meta-analysisEfficacy and safety of oral phenylephrine: systematic review and meta-analysisView study →Reference 4US Food et al. · 2024ReviewAmending Over-the-Counter Monograph M012: Cold, Cough, Allergy, Bronchodilator, and Antiasthmatic Drug Products for Over-the-Counter Human Use (proposed order, Docket FDA-2024-N-4734)View study →}.

The mechanism is α-adrenergic constriction of the nasal mucosal vasculature, reducing mucosal swelling and nasal airway resistance ^{5Reference 5Drew CD et al. · 1978RCTComparison of the effects of D-(−)-ephedrine and L-(+)-pseudoephedrine on the cardiovascular and respiratory systems in man — double-blind studyView study →}.

Importantly it is largely an indirect mechanism: profiling of the ephedrine-type stereoisomers found their most potent action is as substrates of the noradrenaline transporter (NET) — i.e. noradrenaline releasers — with only weak α2/5-HT₇ affinity and no meaningful direct α1 or β activity ^{6Reference 6Rothman RB et al. · 2003In vitroIn vitro characterization of ephedrine-related stereoisomers at biogenic amine transporters and the receptorome reveals selective actions as norepinephrine transporter substratesView study →}.

The limit is effect size rather than absorption.

Multiple-dose decongestant monotherapy beats placebo for subjective congestion by SMD 0.49 (95% CI 0.07–0.92), which the Cochrane reviewers themselves call a small clinical effect ^{7Reference 7Deckx L et al. · 2016Systematic reviewNasal decongestants in monotherapy for the common cold — systematic reviewView study →}; in allergic rhinitis the trial evidence is for combinations (loratadine 5 mg + pseudoephedrine 120 mg twice daily) rather than the isolate ^{8Reference 8Corren J et al. · 1997RCTEfficacy and safety of loratadine plus pseudoephedrine in patients with seasonal allergic rhinitis and mild asthma — randomised controlled trialView study →}.

All of this is isolate data — Ephedra stem delivers pseudoephedrine only inside a variable, mostly-ephedrine alkaloid mixture, so the clean trial figures do not transfer to the herb ^{9,10,11Reference 9Ibragic S · 2015ReviewChemical composition of various Ephedra species — reviewView study →Reference 10Abourashed EA et al. · 2003ReviewEphedra in perspective — a current reviewView study →Reference 11Hong H et al. · 2011Comparison of contents of five ephedrine alkaloids in three official origins of Ephedra Herb in China by high-performance liquid chromatographyView study →}.

It occurs in ephedra.

Mucosal vasoconstriction shrinks swollen nasal tissue, but ephedrine is not the molecule carrying the evidence.

The oral decongestant with the human trial record is its diastereomer pseudoephedrine; ephedrine’s decongestant use is largely topical and historical, and the FDA’s 2004 supplement ban explicitly left approved OTC/prescription decongestant drugs untouched ^{1Reference 1Food et al. · 2004Final rule declaring dietary supplements containing ephedrine alkaloids adulterated because they present an unreasonable riskView study →}.

The mechanism is also complicated by the same α finding as above: ephedrine alkaloids failed to activate α₁ or α₂ receptors directly in cultured human systems ^{2Reference 2Ma G et al. · 2007In vitroPharmacological effects of ephedrine alkaloids on human alpha(1)- and alpha(2)-adrenergic receptor subtypes — in vitroView study →}.

Ephedrine is a contributor to the plant-level decongestant action, and pseudoephedrine is the driver.

It occurs in ephedra.