Tramadol was indeed discovered in the roots of the African Peach Tree by scientists back in 2013, and found to be over 1% of the dry content of the root. Here’s the Chemistry World article on that initial discovery.
That’s not where the story ends though! Researchers in Germany and Cameroon re-tested the samples from the original research, against samples they obtained, and found that in the samples taken in some parts of Cameroon did contain tramadol (though only around 0.00015%), whilst those from southern Cameroon contained no tramadol at all.
The new group theorised that tramadol, readily and cheaply available from markets in northern Cameroon, was being used by the farmers to allow them to work through the day in the hot temperatures, as well as given to their cattle. The cattle were then taking shelter under the trees, and inevitably relieving themselves against them, and providing the source of tramadol detected. This appears to be backed up by the detection of tramadol in the roots of unrelated plants in the area.
The original researcher isn’t having any of it though, claiming that the new research’s claim that the farmers are the source of the tramadol is ‘a formal insult to the African populations and their traditional practices of using plants as medicines’. So, looks like we’ve got a real scientific fisticuffs* on our hands, but for now it seems the natural status of tramadol is unlikely.
*No actual fisticuffs likely.
Here’s the Chemistry World article on the latest study.