The painkiller tramadol is not made naturally by plants despite last year's surprising finding that the drug was present in the roots of a Cameroonian plant (Nauclea latifolia).

Michael Spiteller from the Technical University of Dortmund in Germany and his team analysed plant, water and soil samples in Cameroon and interviewed local residents to track down the true explanation. Farmers in the far north area have been giving tramadol to their cattle, which then excrete the drug and its metabolites into soil and water. The painkiller is subsequently absorbed by plant roots.

The authors say this off-label use of tramadol poses a risk to health because it also contaminates local water supplies.

Angew. Chem. Int. Ed. http://doi.org/f2t7tg (2014)