I could tell the action was curative in intent but figured it must rely heavily on the placebo affect. After all, how could just brushing a leaf on the skin cause any physical reaction since there was so little contact?
Then a second thought occured to me, perhaps the plant was one of the Amazonian variety of stinging nettle being used as a counter-irritant.
Indeed this was the case. I spoke to the two men and they said they were using to plan to relieve “bone pain”. The man’s bare shoulder was covered in welts caused by the poison of the plant. They let me touch the leaves and they stung. My wife jessica had a serious run in with this plant while in the jungle and after the welts went away a few days later her skin began to peel, and the damage is reflected by an uneven tan on that part of her arm.
Counter-irritants work by replacing your former pain with a new pain that is hopefully more tolerable. Some of these work by stimulating the release of internal pain relieving chemicals called endogenous opiates. Why adding more pain, or a different pain results in this opiate release but the original pain did not is still a mystery. Since pain is a reaction our brain creates in response to sensations that it interprets as harmful, the switch of attention away from the original pain, and towards a pain perceived as curative is likely responsible fora large portion of the counter irritants success. In any case, counter irritants, and their less aggressive cousins the counter stimulants do provide moderate pain relief. Icy-hot, electrical stimulation, and painful massage are western versions of this Amazonian stinging leaf.
Most of the shamanistic remedies I have seen either rely on pharmacologic properties of inconsistent concentration or pure placebo effect* but this stinging leaf remedy has another mechanism going for it: counter irritation. I imagine that the stinging nettle of North America can be used in a similar way.
*The most hilarious shaman remedy I have seen is the “supi siki panga.” The name means “gassy butt leaf” in Quechua and the prescription is just as funny as the name. The patient affected my flatulence is brought to the place in the forest where the leaf grows. The leaf is picked and waved back and forth behind the patients derrière after which the leaf is tossed in the air and the patient has to run as far away as possible before the leaf hits the ground. Mercy on the septuagenarian suffering from flatulence who is too arthritic to run!