Worldwide, one of the drivers of substitution and adulteration is the cost of the natural resources (plants, animals, fungi) that are ingredients of traditional medicines. Relatively few studies have been done that link prices of traditional medicine ingredients to what drives changes in price, yet this is an important topic. Theoretically, prices have been widely considered as an economic indicator of resource scarcity. Rare, slow growing medicinal plants sell for high prices and common, less popular species for low prices. Price levels also influence the viability of farming vs. wild harvest (and incentives to overharvest high value species when tenure is weak). Prices can also influence the harvesting or buying behaviour of harvesters, traders or manufacturers. When prices are high, then there is a greater incentive to use cheaper substitute species or adulterants. As previous studies on herbal medicine ingredients have shown, adulteration applies in a wide variety of cases, including to some Traditional Chinese Medicine (TCM) species.