Depending on which species of psilocybe one finds. If it is a P. cubensis, the chances of poisoning are virtually nil. On the other hand, there is one species, P. azurescens ("Flying Saucer") mushroom which has been known to cause temporary paralysis in some people. This is not due to psilocybin, however.
During the Mushroom Symposium, I have asked a mycologist by the name of Dr. Paul Stamets, if this momentary paralysis was due to the transformation product of either psilocyn or psilocybin and he told me that it wasn't. It was due to another compound which can be eliminated by boiling this species briefly into tea.
If you check with the MERCK INDEX, you will find that psilocybin is not as readily destroyed by hot water as certain ergolines are. Indeed, the natives of South America brew the leaves of Psychotria viridis and Banisteriopsis caapi during their Ayahuasca ceremonies. The Chacruna leaves contain DMT and are not decomposed by the temperature of boiling water.
Psilocin is not as stable as psilocybin, but not to the degree where a quick boiling of P. azurescens would destroy the product. appearantly, the other substance which is unrelated to the tryptamines has a lower boiling point and can be safely removed by this method.
All that aside, P. cubensis is not a poison as we generally understand it to be.
In California one must be careful and not mistake the deadly Gallerina autumnalis for Psilocybe cyanescens. The way to identify this deadly fungus is with its saffron or light brown/orange colored spores during a spore print. Also, it does not bruise blue like P. cyanescens will. Some examples of Gallerina I have seen have "wavy" caps like cyanscens, but most of them lack the nipple and none of them bruise blue or have purple/brown spores.
For more information on spotting the deadly fungi during a foray, please click here:
http://www.mikoweb.com
and look up under California mushrooms, then click on the name of the species in question.
Good luck, stay safe, good health with happiness and peace.
Love and Spiritual Discovery
--NN