This episode of Nature Notes was previously broadcast on December 16, 2011 and was written by Jack Copeland of the Chihuahuan Desert Research Institute.
If the deserts of the southwestern United States and northern Mexico were in the pharmacology business, then creosote would be their perennial best seller. The therapeutic applications for this greasy, smelly, tenacious desert dweller would make any biotech CEO green with envy. Traditional healers have used creosote to treat over 40 human maladies, from acne to venereal disease. What are its medicinal properties? And why is it such a pharmacological trove?
Creosote, also known as greasewood, is an evergreen shrub, which thrives in the Chihuahuan, Sonoran and Mojave deserts. It features prominently in the Papago tribe’s creation myth. These Native Americans believe greasewood was the first green thing which grew from a mound of soil shaped by the Earth Maker spirit. Science supports the legend. Radiocarbon dating of one extensive expanse of creosote clones in the Mojave Desert revealed the plant’s age to be between nine- and eleven-thousand years old.
Creosote won’t win any congeniality contests. A combination of highly efficient water-absorbing roots and toxic chemical secretions inhibit the growth of nearby plants. Bitter resinous compounds repel herbivores. Other compounds make its leaves unappealing to all but one type of grasshopper. Once established, not much can challenge the greasewood’s hegemony.
A single shrub produces a great variety of chemicals, including forty-nine volatile hydrocarbon oils. After a summer rain, creosote releases a strong-scented potpourri of camphor, vinyl, and methyl-ketones. This cocktail of oils, flavonoids, and waxes protects the plant from heat, ultraviolet radiation, and water loss.
About five to 10 percent of the dry weight of creosote leaves consists of a powerful antioxidant, known as NDGA. This compound endows it with antibacterial, antifungal, antiviral, anti-inflammatory and analgesic properties. The plant’s leaves, stems, twigs and branches have all had medicinal applications: as a poultice or liniment for rashes, wounds, and venomous bites; wrapped around swollen limbs for rheumatism; or boiled as a tea to induce vomiting. Traditional healers have prescribed creosote for menstrual cramps, infertility, tuberculosis, syphilis, diabetes, gallstones, kidney stones, even dandruff.
There have also been veterinary applications. The late Marfa veterinarian, Dr. Charlie Edwards, chronicled a treatment early West Texas ranchers used to treat screwworms in cattle and horses. After dosing the worms with benzol or chloroform, ranchers applied a homemade smear called tecole, consisting of pine tar, tincture of iodine, and a solution of creosote extract. In his memoir, Up to My Armpits, Edwards wrote that “this black, foul-smelling smear was something that no self-respecting fly would come close to.”
Recent laboratory studies suggest that creosote’s primary antioxidant, NDGA, does in fact have antiviral activity against HIV, herpes simplex, and human papilloma viruses.
But detracting from creosote’s healing reputation are animal studies and anecdotal reports in humans documenting liver and kidney toxicity. Several deaths have even been reported, especially with chronic use or high dosage. The FDA banned NDGA as a food preservative in 1970, although the chemical is still used as an effective natural fiber preservative. Further research is required to better establish therapeutic efficacy, proper dosage, and toxicity associated with creosote-derived compounds.
In 1962, the Atomic Energy Commission detonated a thermonuclear explosion at Yucca Flat, Nevada. Twenty-one creosote shrubs were present on the site prior to the blast. Ten years later, 20 of these original creosote bushes had re-sprouted. Surely a species with such mythic adaptability and perseverance is worthy of both research and reverence for a long time to come.