An interesting study I'd not seen before now, thank you to Don Shadow for bringing this to my attention. I thought it may be of interest to others and so worthy of sharing.
Matshushima, Y., Shirota, O., Kikura-Hanajiri, R., Gosa, Y. & Eguchi, F. et al. (2009) Effects of Psilocybe argentipes on Marble-Burying Behaviour in Mice. Bioscience, Biotechnology, and Biochemistry, 73,8: 1866-8.
Psilocybe argentipes is a hallucinogenic mushroom. The present study examined the effects of P. argentipes on marble-burying behavior, which is considered an animal model of obsessive-compulsive disorder. P. argentipes significantly inhibited marble-burying behavior without affecting locomotor activity as compared with the same dose of authentic psilocybin. These findings suggest that P. argentipes would be efficient in clinical obsessive-compulsive disorder therapy.
...we obviously need to be cautious when attempting to extrapolate and infer from animal model studies (in this case an animal model of OCD), but I thought this was quite an interesting finding:
"In the experiments, when mice consumed P. subcaerulipes, it significantly inhibited their marble-burying behavior, but, unlike an equivalent dose of purified psilocybin, did not affect locomotor activity. Further, the mushroom was more effective than purified psilocybin in inhibiting the behavior, and lower doses were required. Based on these results, the authors suggest that the mushroom has the potential "to be efficient in clinical obsessive-compulsive disorder therapy".
This is at the very least suggestive that there could be secondary compounds in the mushroom that modulate or synergise with the psilocybin in mushrooms to some degree, beneficially in this case (even if it is the presence of psilocybin/serotonin precursors in the mushroom) and these compounds may be lacking when ingesting pure synthetic psilocybin. Much of the psilocybin mushroom potency data is out of date, and more research on the potential modulating influence of secondary compounds found in mushrooms (such as baeocystin/norbaeocystin and others) is certainly warranted.