Assuming we're in portugal where drugs are decriminalized or in a Torah law society (So not taking into account Dina D'malchusa), what are the halakhic considerations regarding consuming psychedelic mushrooms? The reason I ask my question is because I saw this question about smoking marijuana and I believe that many of the factors that motivated Rav Moshe's teshuva cited in the answer prohibiting marijuana are not relevant to mushrooms.
Could they be permitted for medicinal purposes? Psychedelic mushrooms been used in many psychological treatments, as well as a known cure for cluster headaches. See www.clusterbusters.org
Could they be permitted for recreational use, considering the facts that they are non-addictive and nearly impossible to overdose on.
Mushrooms release chemicals in your brain, mainly serotonin. A typical trip lasts 4 hours. After the trip is done you can continue to take mushrooms but they have no effect as all of the available serotonin has been released. It takes 5-7 day to replenish your serotonin so you could only trip about once a week. You could take them every day if you wanted to but you would have no psychotropic effect from them until you gave it a rest for about a week. Most of this is anecdotal as the government has made this a schedule 1 drug. But if you search the web you'll find a zillion sites that state this. Most of them say only about once a month or twice a month works. But it's really about a week. Here's a site but there are many more. http://www.psychonaut.com/mushrooms/26445-waiting-period-between-2-trips.html
After a certain amount the drug psilocybin which is the active ingredient doesn't do anything to you because you've released all of your serotonin. The mechanism is more complicated then what I'm describing but this should suffice. LD50 is the amount of a drug that is required to cause death. The LD50 of Psilocybin is about a pound, but that's the active ingredient and there's only a small amount of the drug in a mushroom. They estimate to achieve the LD50 you'd have to eat from 6 pounds to more than your bodyweight in mushrooms(depends on potency, but I'd bet it's a lot more than 6 pounds), which is impossible to do. Again there are many sites that discuss the LD50 of mushrooms. Here's one. http://www.psychonaut.com/mushrooms/26445-waiting-period-between-2-trips.html
Also please don't respond that all intoxicants are not permissible, as alcohol is an intoxicant and is permissible to drink. It's even suggested to get drunk on holidays such as Purim and I've seen a few Rabbis shikered on Simchas Torah as well!