Benefits
Traditional throat-soothing tea in European herbal use
Mullein flower tea is registered in the European Union as a traditional herbal medicine for sore throat that comes with a dry cough and cold. That status rests on at least 30 years of documented use, 15 of them within the EU, rather than on trials: the regulator found no clinical data. No study has measured whether the tea eases or shortens a cold.
Mucilage content behind its traditional demulcent use
The flowers contain roughly 2 to 3 percent water-soluble polysaccharides, and pharmacopoeia-grade flower must swell in water to a set minimum. EU reviewers concluded that mullein's traditional role in cough and cold is chiefly as a demulcent, a slippery film over an irritated throat. The proposed effect is a local coating; no study has measured it in people.
Expectorant use and laboratory tests of mucus transport
Traditional herbals call mullein an expectorant that loosens chest mucus, usually crediting its saponins. In the only mucus-transport test EU reviewers could find, a water extract of the flower did not change mucociliary transport in isolated frog ciliated tissue, and saponins have not been confirmed in one of the three official flower species. No human study has measured mucus clearance.
Respiratory virus activity seen only in cell culture
A freeze-dried infusion of mullein flowers lowered influenza A and B virus titers by 1 to 3 log units in cell culture and directly inactivated herpes simplex virus, though it did not inactivate influenza particles. No study has tested whether drinking the tea changes the course of a cold or flu in a person.
Anti-inflammatory activity in cell and animal studies
A polyphenol-rich flower extract cut an inflammatory adhesion molecule by more than half in human endothelial cells, but the same extract did not reduce paw swelling in rats. Isolated constituents such as verbascoside and aucubin reduced paw swelling in rats at oral doses of 100 to 150 mg per kilogram, far more than the 12 mg or less of either found in 2 g of flower.
Mechanism of action
Mucilage polysaccharides and throat coating
Mullein flower holds about 2 to 3 percent water-soluble acidic polysaccharides, mainly a highly branched arabinogalactan, plus a neutral arabinogalactan and a xyloglucan. In hot water these swell into a viscous solution that can coat the mouth and throat, the proposed basis of the soothing, demulcent use.
Saponins and the expectorant theory
Triterpene saponins such as verbascosaponin and the thapsuins have been isolated from mullein flowers and are the usual explanation for an expectorant effect. The only published content figure is tiny and methodologically weak, none were confirmed in V. densiflorum flowers, and a flower extract did not alter mucociliary transport in vitro.
Iridoids and phenylethanoid glycosides
The flowers carry iridoid glycosides such as aucubin and catalpol and the phenylethanoid verbascoside; in cell studies verbascoside and related phenylethanoids dampen nitric oxide and leukotriene production. Amounts vary widely by species: verbascoside is about 0.6 percent of V. densiflorum flower but only a trace in V. phlomoides.
Direct antiviral and antibacterial action in vitro
In cell culture, flower infusions reduced influenza virus yields and inactivated herpes simplex virus, and extracts inhibited several bacteria in dish assays. These effects come from extract applied straight to cells or microbes; absorption and blood levels after drinking mullein have never been measured.
Clinical trials
Laboratory study of a lyophilized flower infusion of Verbascum thapsiforme; no human participants (Zgórniak-Nowosielska et al. 1991, Arch Immunol Ther Exp (Warsz))
Cell cultures infected with fowl plague virus, several influenza A strains, an influenza B strain and herpes simplex virus.
Influenza titers fell by 1 to 3 log units and herpes simplex titers by 2.3 log. The infusion inactivated herpes simplex virus directly at 300 micrograms per mL but did not inactivate influenza virus. No human study has tested these effects.
Laboratory and animal study of a water and n-butanol extract of Verbascum phlomoides flowers; no human participants (Grigore et al. 2013, Pharm Biol)
Human umbilical vein endothelial cells stimulated with TNF-alpha, and a rat paw edema model.
The extract contained 4.18 percent total polyphenols, mainly caffeic, ferulic and rosmarinic acids and quercetin; acteoside was not detected and aucubin appeared only in traces. It lowered ICAM-1 expression by 55 to 58.8 percent in cells at 100 and 200 micrograms per mL but did not reduce paw edema in rats. The authors judged the polyphenols to have only a weak influence on anti-inflammatory activity.