They can temporarily instill psionics in a character once per day. If you take it more than once in a day, you'll just go temporarily insane. Remember when I talked about the Shadow Masters and how they're not master economists? Well, here's where I get back to that. Psisheen Mushrooms can be distilled into a substance called Psisha worth 100.000$ per pint. Now, Shadow Masters can, with special arcane secrets, distill Psisha into an even more potent substance called Psisha Adreemus. It takes 1.250 gallons (10.000 pints for those trying to keep score at home) to produce a single pint of Psisha Adreemus. Which sells for 1.000.000.000$ - exactly the value of the raw materials. I'm not any kind of a businessperson but even I can see that this makes no sense. Evidently, Shadow Masters don't particularly value labor.
Cited from Let's read Synnibarr!