In 2013, researchers reported that tramadol was found in relatively high concentrations (1%+) in the roots of the African pin cushion tree (Nauclea latifolia). In 2014, however, it was reported that the presence of tramadol in the tree roots was the result of tramadol having been administered to cattle by farmers in the region: tramadol and its metabolites were present in the animals' excreta, which contaminated the soil around the trees. Therefore, tramadol and its mammalian metabolites were found in tree roots in the far north of Cameroon, but not in the south where it is not administered to farm animals.
A 2014 editorial in Lab Times online contested the notion that tramadol in tree roots was the result of anthropogenic contamination, stating that samples were taken from trees that grew in national parks, where livestock were forbidden; it also quoted researcher Michel de Waard, who stated that "thousands and thousands of tramadol-treated cattle sitting around a single tree and urinating there" would be required to produce the concentrations discovered.
In 2015, radiocarbon analysis confirmed that the tramadol found in N. latifolia roots could not be plant-derived and was of synthetic origin.