Mullein: Background. Actions

2010

Common Name

Mullein

Other Names

Aaron’s rod, Adam’s flannel, blanket herb, bunny’s ears, candlewick plant, flannel-leaf, great mullein, Jacob’s staff

Botanical Name / Family

Verbascum densiflorum, Verbascum phlomides, Verbascum thapsus (family Scrophulariaceae)

Plant Parts Used

Flower — dried petals, leaves

Chemical Components

The flower contains water-soluble mucilage, polysaccharides, flavonoids (including apigenin, luteolin, kaempferol and rutin), caffeicacid derivatives, iridoid monoterpenes, triterpene saponins (verbascosaponin), sterols and invert sugar.

One of the most investigated constituents isolated from plants in the Verbascum species is verbascoside, an iridoid glucoside. Whether the pharmacological effects demonstrated for this single constituent can be extrapolated to explain those for mullein is uncertain, as the effects of any herb are due to a number of phyto-constituents and their interaction with each other and the body. As such, information about verbascoside is included here in order to provide a further insight into the herb, but it should be interpreted accordingly.

Verbascoside has also been isolated from other herbs such as Verbena officinalis, Echinacea purpurea roots, Euphrasia pectinata, Phlomis longifolia, Pedicularis plicata, Duranta erecta, Marrubium alysson, Leonurus glaucescens and Balotta nigra.

Historical Note

Over the centuries, mullein has been used in various ways. Taken internally, it has been used to treat respiratory conditions and tumours; applied topically, its use has been to relieve itch and dress wounds. It was also used to make candlewicks for casting out evil spirits. Dueto its robust nature, mullein is now considered a serious weed pest of roadsides and industrial areas in countries such as the USA.

Mullein: Main Actions

Mullein has not been significantly investigated under clinical trial conditions, so evidence is derived from traditional, in vitro and animal studies.

DEMULCENT AND EMOLLIENT

Traditionally, these actions were thought to occur primarily within the respiratory system, especially the lungs. However, topical preparations of mullein also exert an emollient action on the skin. This is most likely due to the herb’s high mucilaginous content.

Clinical note — Natural mucilages found in herbs

Mucilages are large, highly branched polymeric structures made from many different sugar and uronic acid units. They are hydrophilic and are capable of trapping water, causing them to swell in size and develop a gel-like consistency. The gels tend to have soothing properties and can be broken down by bowel flora when taken internally. They are known to have beneficial effects on burns, wounds and ulcers when applied externally, and on gastric inflammation and irritation and diarrhea when taken internally.

ANTIMICROBIAL

Antiviral action

Mullein extract exhibits antiviral activity against fowl plague virus, several influenza A strains and influenza B strain, as well as HSV in vitro. Antiviral activity has been demonstrated for both infusions and alcoholic extracts.

Antibacterial action

In vitro studies have demonstrated antibacterial activity for mullein extracts (aqueous, ethanol and methanol) against Klebsiella pneumonia, Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli. Of the three extracts tested, aqueous extract exhibited the strongest antibacterial action.

ANTITUMOUR

Some plants, such as mullein, were used in folk medicine as sources of antitumour remedies. An in vitro study has identified inhibitors of protein biosynthesis in Verbascum thapsiforme flowers. Researchers found that a saponin glycoside and its aglycon, isolated from the flowers, directly inactivates ribosomes. The constituent, verbascoside, has been shown to inhibit telomerase activity in human gastric carcinoma cells in test tube studies, resulting in inhibition of tumour growth. Cytotoxic effects for verbascoside have also been identified against rat hepatoma and sarcoma cells, and cytostatic activity on human epithelial carcinoma cells.

Mullein: Other Actions

The verbascoside constituent demonstrates antioxidant activity in vitro. The saponins in mullein are thought to exert an expectorant activity; however, further investigation is required to confirm this.