Question of the Week Podcast

Question of the Week episode

Tue, 6th Nov 2012

Why do some fungi produce hallucinogens?

Psilocybe semilanceata (c) Alan Rockefeller

This week we find out why certain mushrooms contain hallucinogens, plus we ask, how long could you survive by eating your own limbs?

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  • Why do fungi make hallucinogens?

    Hello Naked Scientists! I have a question(?) concerning both bacteria and fungi. How have some fungi evolved to produce substances that are hallucinogenic like psilocybin? What's the benefit and cost of producing such chemicals? What is known about the group of genes that prod...



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Q. Why do fungi make hallucinogens?

A. Self preservation : in certain circumstances there is natural selection for the plants/fungi which poison the animals consuming them.


RD, Tue, 30th Oct 2012

The hallunicogens most commonly associated with fungi are psilocybin/psilocin (tryptamine alkaloids -related to serotonin etc) present in the mushroom (basidiocarp), notably of Psilocybe/Panaeolus spp. 

The sole function of a mushroom is to disperse the spores of the fungus. The standard gilled mushroom has evolved to optimise airborne dispersal of spores and presumably is more effective if the mushroom lasts a long time (ie doesn't get eaten etc).

However, for at least some mushroom-forming species, spore dispersal by mammals (squirrels, voles, deer etc) following mycophagy is also thought to be important (eg. Ashkannejhad andHorton . New Phytologist, 169:345-354) and it is not uncommon to see 'nibbled' mushrooms. Also there are diverse insects (eg fungus gnats) that inhabit mushrooms -presumably leading to more rapid decay.

So there may be a trade-off between deterring animals to maximise wind dispersal and the role of animals as vectors. Toxins, hallucinogens, volatiles and coloration could all play a role in these processes.

Just as with colours (humans are a highly visual species compared to eg sheep) and toxins (eg the cacao metabolite theobromine is pleasurable to us by toxic to dogs), the same compound may have very different effects in humans vs other mammals.  It seems more likely that the various biologically active compounds in mushrooms evolved to attract/deter mammals/insects other than humans, so the effects on us are probably incidental.

That said, there are many more examples of plants which contain psychoactive/toxic metabolites, so the particular fascination with 'magic mushrooms' probably relates to a more general 'mycophobia'. How often do you notice a plant and wonder to yourself "Can I eat that? Is it poisonous?")
Capcwyr, Tue, 30th Oct 2012

This is what I was thinking too. What's fascinating is that are these psilocybin chemicals in any way common in the plant or the bacterial kingdom or just unique to fungi? Are the chemicals present only in the basidiocarp (mushroom) or also in the hyphae as well? They are secondary metabolites, am I right? So where and how are they produced in the fungal cell?

I hope I'm not getting carried away. Addu, Tue, 30th Oct 2012

Sorry, better to mention that I posted this question of the week. ;) I'd really like to have some discussion about how common these chemicals are. But mainly of course why fungi do bother to make hallucinogens and how they produced them. Addu, Wed, 31st Oct 2012

Keep in mind that some mushrooms also produce deadly toxins. 

I thought I would make a comparison between Amanitin, a deadly mushroom toxin, Psilocybin, a mushroom hallucinogen, and Serotonin, a human neurotransmitter.

I was surprised about the size of the amanitin molecule.  However, I wonder if psilocybin is an amanitin precursor, or perhaps an incomplete form of the larger molecule.  The addition of the phosphate group is interesting.

The similarity of psilocybin to serotonin would be related to the hallucinogen effects. CliffordK, Wed, 31st Oct 2012

There is another concoction of hallucinogens (though not fungi related) made from a brew called Ayahuasca as used by Amazonian tribes. The Banisteriopsis caapi vine contains a monoamine oxidase inhibitor (MAOI) and is mixed with the leaves of dimethyltryptamine (DMT)-containing species of shrubs from the genus Psychotria.

It is said the foul tasting combination of "herbs", apart from making one vomit, literally knocks one into an elevated change of consciousness where one experiences the spirit world. Users report of life changing experiences after subsequently grounding themselves. FuzzyUK, Tue, 6th Nov 2012

the blue stuff is a known slug killer azrael, Mon, 17th Dec 2012

pretty sure it is the orally active dmt that knocks one into an altered state. it doesn't taste that bad. very bitter. i've tasted much worse. azrael, Mon, 17th Dec 2012

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