Coca

On the Inca Trail, coca leaves are offered at every opportunity. You can buy them from the market at the bus drop off, you can get them from farm-side stalls on the first day of the walk. They are offered up at breakfast, coffee (coffee thick enough to pave a road), lunch and supper to dip in hot water, enough to nick supplies to carry up the mountain to stick between lip and gum. The plants are cultivated in shady clearings in the forest and look a bit like pruned bay trees. Me, I helped myself, and spat the stuff out when it got too disgusting. I am not sure what good it does, but it is meant to help with the altitude (there really is an oxygen shortage up at 3 miles high: walk/climb ten metres, take a 2 minute breather) and the sheer hard work of employing porters to carry your rucksack. Whatever your budget.
Naturally, I brought none back to the UK as that would doubtless have been illegal, but I do wonder why I have felt slightly floaty for the last 2 weeks.
When refined, the leaves provide a significant income for certain people in Colombia and Guiana etc, who often re-invest that money to the benefit of local people (unlike their venal, corrupt US-Sponsored governments, especially Colombia), but it does attract the attention of the US government, who rather than strafe and bomb their own citizens (the users of the end product), prefers to poison and kill poverty stricken farmers in the Andes. So much harder to sort their own problems out at home. No wonder most South American governments are turning on the US: if they were ever listening to their own people, now's the time, and screw the esqualidos.