White Horehound: Marrubiin and Medical Discovery

Perhaps better known some decades ago in connection with oddly flavored cough lozenges, the white or common horehound is a plant (Marrubium vulgare) easily grown at USDA Zones 4 - 8 in gardens located in nearly every state of the union. In fact, horehound grows so well that in some states it is considered a weed. Not particularly attractive, the horehound plant may hold more of a nostalgic place in gardens, among the other herbs. Rather than relegate the horehound plant and its extracts and lozenges to grandma's closet, it is wise to consider the abundance of new insights, botanical and medicinal. Let's begin with horehound's active component.

Active Component of Horehound

Of primary importance in M. vulgare is Marrubiin-a diterpenoid¹ lactone² that melts at about 155 degrees C. It shares many similarities with the uterine anti-cancer agent, taxol, itself a diterpene. Marrubiin is produced and secreted by specialized "glandular trichome" leaf cells.

Marrubiin repels certain insects, indicating a possible future use in insecticide formulations. It is also antiviral and antibiotic. With only slight chemical modification, such as breaking open its lactone ring and de-esterification to produce marrubiinic acid, marrubiin is being tested for the production of pain-killing analgesics.

Marrubiin Production

One great discovery is that by providing enhanced nutrition to the horehound plant, marrubiin production has been increased as much as 30 fold, thus marrubiin is available in surprisingly large quantities naturally. There are, of course, synthetic chemical methods for producing marrubiin. A discussion of the structure and synthesis of marrubiin may be downloaded free from the National Center for Biotechnology Information (NCBI) website.³

Why Not Grow Some Yourself?

The horehound plant, of the mint family, is very inexpensive to purchase. It thrives in full sun. It does well even in relatively dry, poor soil. The plant develops almost heart-shaped, crinkly, and downy leaves; it produces white blossoms in mid-summer. It may take two seasons to do so. The leaves can be broken and made into a tea, or they can be cut, dried, and stored. Be aware that horehound self-seeds, and can spread readily, so feel free to harvest frequently.

¹ Terpenes and terpenoids are organic compounds that are essentially combined isoprene units. See the article, "The Chemistry of Nature: The Isoprene Rule."
² Lactones are esters theoretically formed from an alcohol and an acid group both on the same molecule that attach with elimination of water to produce a ring structure.
³ NCBI article.

References and Resources:

USDA Natural Resources Conservation Service - Horehound

PubMed Central - "Anti-proliferative effect of horehound leaf... on human colorectal cancer cells," by Yamaguchi, et. al.

Cal State - CSU Bakersfield Researcher Earns Accolades