What is it?
An extract of the root of osha, Ligusticum porteri, a slow-growing plant in the parsley family that lives in high mountain meadows and forests of the Rocky Mountains and northern Mexico. Native American tribes of the region have long used the root for pain and for respiratory and digestive complaints, usually chewing it or making it into tea. Today the root is traded for herbal products, and it also appears in some personal care products, such as tooth polishes.
Key information
- United Plant Savers puts osha on its At-Risk list of native medicinal plants and recommends using cultivated plants whenever possible.
- Osha is hard to cultivate, so most commercial osha root is harvested from the wild.
- Poison hemlock, a toxic plant in the same family, is one of the look-alikes that grows within osha's range.
- We found no formal safety assessment of osha as a cosmetic or supplement ingredient.
More information
Osha lives only in the Rocky Mountain subalpine zone, from about 1,000 to 3,500 meters (5,000 to 11,500 feet), in Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah and Wyoming and in northern Chihuahua, Mexico. A 2023 analysis of root from Colorado’s San Juan Mountains detected 30 to 40 compounds, including p-cymene and ligustilide.
Osha has had little safety testing. We found no review of it by the Cosmetic Ingredient Review or the EU’s Scientific Committee on Consumer Safety, and no studies of skin irritation or allergy. In a 2007 study of acute toxicity in mice, osha extract was among the four most toxic of 15 Mexican medicinal plants tested.
The better-documented concerns are about sourcing. Osha grows slowly and is hard to cultivate, so the vast majority of commercial root is wild-harvested; an industry survey for 2011 to 2017 found average demand of about 1,765 pounds a year, which United Plant Savers calls a low estimate. United Plant Savers lists osha as At-Risk and recommends cultivated material whenever possible, with very limited, carefully monitored wild harvest. Harvesters can also confuse osha with look-alikes in the parsley family, including poison hemlock (Conium maculatum), which is toxic. We found no published reports of hemlock in commercial osha products, but the risk is a reason to look for suppliers that verify plant identity.
Reality check: long traditional use is not the same as tested safety. The amount in a tooth polish is small, but osha is unreviewed, mostly wild-harvested, with overharvesting reported in some areas, and grows alongside a toxic look-alike.
Sources: United Plant Savers: Osha (Ligusticum porteri); United Plant Savers: Species At-Risk List; Journal of Undergraduate Chemistry Research (2023): Analysis of southwestern Colorado Ligusticum porteri by gas chromatography-mass spectrometry; Journal of Ethnopharmacology (2007): Acute toxicity and mutagenic activity of Mexican plants used in traditional medicine
