The Surprising Relationship Between Wintergreen and Aspirin
I remember riding my horse on trails through the New York woods as a child and stopping to break off a twig of the black birch tree, sometimes called sweet birch. Native Americans understood the properties of these trees and others, hundreds of years before my horse and I blazed through the woods. I learned to identify Betula lenta by its scaly brownish-black bark and unmistakable minty fresh aroma. I knew where the trees grew and could counsel the inexperienced about a simple scratch-and-sniff test to distinguish black birch from black cherry whose bark looked similar—scratch the bark of a twig and the sweet minty scent of oil of wintergreen meant black birch, not black cherry. Though I enjoyed this local treat in those early days, little did I appreciate the medicinal properties of the black birch’s crushed twigs and foliage.
Betula lenta is deciduous and grows between 50-75 feet tall, with a native range from Southern Maine down the east coast to the Appalachian Mountains of Georgia and Alabama. The familiar scent of wintergreen, present in the wood, is often used as a flavoring agent in food and drinks, including candy and gum, as well as in various personal care products. Native Americans were well aware of the healing benefits of the oil of wintergreen, particularly as an anti-inflammatory and antipyretic (fever reducer.) And the willow tree bark was the source of a similar compound, still a miracle of modern medicine—acetylsalicylate or aspirin.
While oil of wintergreen (methyl salicylate) was once harvested from the bark of young black birch and the leaves of Gaultheria procumbens, a small creeping shrub, it’s now produced from wood alcohol (methanol) and salicylic acid. Salicylic acid was developed from salicin, found in the bark of willows, particularly the white willow, Salix alba. Salicin obtained its name from Salix, the genus of the willow tree. Salicin was later refined into a stronger compound called salicylic acid. Finally, with the addition of an acetyl group, the compound became known as acetylsalicylate or acetylsalicylic acid (ASA), or aspirin, as we know it today. Aspirin is a drug used to treat pain, fever, and inflammation and is considered a nonsteroidal anti-inflammatory (NSAID).
Both these compounds, methyl salicylate (oil of wintergreen) and acetylsalicylate (aspirin), are toxic in high doses. This includes overuse of topical preparations prescribed to relieve joint or arthritic pain, or muscle pain when rubbed into the afflicted area. A single teaspoon of concentrated oil of wintergreen contains 5 g (grams) of methyl salicylate, equivalent to 7.5 g of aspirin. Fatalities in children have occurred with ingestion of 5mL (about 1 teaspoon) or less of the concentrated oil. An acute, mild to severe aspirin ingestion is anywhere from 150-500 mg/kg—for example, a 68 kg (150 pound) person would have to ingest 13,600 mg to 20,400 mg or 13.6 g to 20.4 g. These overdose scenarios require emergent medical attention to prevent the complications of acute intoxication and even death.
When I travel in the woods now, particularly on a snowy wintery day when trees are bare of leaves, and only their bark gives them away, I appreciate more of what those living off the land understood about ethnobotany—just enough of the remedy to make you better and not so much as to make you ill.