The structure of the mushroom’s active ingredient is noteworthy among other things, because it is closely related to serotonin as well as because, like lysergic acid and LSD, it incorporates an indole derivative that is substituted at position 4. In my opinion psilocybin and psilocin deserve further attention in experimental psychiatry and as prototypes for chemical modification. But psilocybin research has already produced useful information and led indirectly, as LSD did, to important new medicines.