I believe that shaman originally drank their own urine to have repeated trips and discovered the reduced toxicity. I suspect using reindeer came later as a way

I believe that shaman originally drank their own urine to have repeated trips and discovered the reduced toxicity. I suspect using reindeer came later as a way to outsource the toxicity reduction. There are other ways to prepare Fly Agaric (Amanita Muscaria) to reduce toxicity. Baking at a low temperature with lemon juice simulates the digestive process enough to help.