Were psilocybin mushrooms ever traded in Post-Rome Europe, brought there by merchants, or in any way accessible to average folks? Were early colonists ever exposed to them in any way?

For some reason I can't view the other comments on this post, so apologies if I'm doubling up things that have already been written. I'm a historian of the 4th and 5th century Roman Empire and I've also written and researched a fair bit on the history of psilocybin mushrooms in European history, so I feel I've got relatively good background to give a well qualified answer on this one.

I'm afraid the answer is "no, they weren't". Andy Letcher's book 'Shroom' is a FANTASTIC read and much the best thing out there on psilocybin culture, and as he points out there is simply no evidence that Europeans ever practiced magic mushroom use before the 'discovery' of the practice among central Americans in the 20th century. Plenty of psilocybin mushrooms are native to Europe, but there is simply no evidence that anyone knew what these mushrooms were capable of. Obviously, people would have ingested them from time to time, but then as now people were cautious about fungi and anyone who had eaten magic mushrooms would presumably have believed that they had simply been poisoned. Early scientific literature on mushrooms from the 18th and 19th century shows absolutely no awareness that there was anything special about the 'magic' species, though they are occasionally listed a poisonous. So whilst we can - and lots of people do - hypothesise that they will have been ingested before the C20, there is literally zero evidence to build a case for any kind of systematic and intentional use of these mushrooms as drugs. Anyone claiming different is generally getting very creative, and suggestions (for example) that Viking berserkers used magic mushrooms are based on no evidential foundation of any kind. Likewise, books like Robert Graves's 'The White Goddess', which find 'evidence' for ancient magic mushroom cults and for a long tradition of European magic mushroom use are almost entirely works of imaginative fiction by people who really love magic mushrooms and want to give their hobby an exciting cult history to go with it.

It's boring, I know - it would be fun to think that it was otherwise, but on the basis of the evidence we possess the answer just has to be no: until the 1950s, no one outside of traditional communities in Central America had any idea that these mushrooms could induce visions or be used as medicine.