When Terence McKenna discovered a technique for home-cultivation of psychedelic mushrooms in the 1970s, he transformed a rare entheogen, known mainly to mycologists, shamans and mushroom hunters, into a common and widely proliferated hallucinogen. At the time, magic mushrooms weren't illegal and Terence set up shop in Northern California, acting as probably the sole grower until the book he had written under a pseudonym with his brother Dennis was published, the Magic Mushroom Grower's Guide, (still in print today). "Shrooms" have been on the standard psychedelic menu ever since, and mushroom cultivation is widespread. Until he stopped in the 1980s, Terence would output upwards of 70 pounds every 6 weeks.

When these mushrooms first entered the countercultural underground, there was very little common knowledge on how to identify the actual psychedelic varieties. It was occasionally the case that dealers were selling ordinary grocery store mushrooms laced with LSD. In recent years, knowledge of psychedelic mushrooms is widely available among the community (and on the internet). There are many kinds of psychedelic shrooms you might encounter (depending on which part of the planet you live in), but it should never look like an ordinary white mushroom (Agaricus bisporis). 99% of hallucinagenic mushrooms on the underground market are dried Psilocybe cubensis (also known as Stropharia cubensis), with characteristically blue bruises on their white stems and brownish-orange caps with possibly golden facets. There are some other psychtropic species out there. Please be certain that you recognize the mushrooms you are ingesting.

See also:
Psychedelic Guide: Mushrooms
Mushroom trip #1
Psilocybe cubensis
Liberty Cap