Some Psilocybe mushroom eaters, in an effort to avoid LSD and PCP tainted varieties sold on the street, try to pick their own mushrooms. In theory, this should be easy to do. Psilocybe (species containing psilocybin) mushrooms grow naturally around the world and in the United States particularly in the Pacific Northwest and southeastern states. Mushroom hunters often seek out cow pastures, riverbanks, pine forests, and wood chips in search of over 90 known species of Psilocybe mushrooms. The problem, though, is that it is very difficult to tell the difference between Psilocybe and other poisonous mushrooms. Psilocybe and poisonous look-alikes can grow side by side.

According to the U.S. Food and Drug Administration Center for Food Safety and Applied Nutrition Foodborne Pathogenic Microorganisms and Natural Toxins Handbook, "Mushroom poisonings are almost always caused by ingestion of wild mushrooms that have been...