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Psilocybin Pharmacology.

The primary psychoactive active compounds produced by the psilocybin mushroom are psilocybin and psilocin. It also produces other hallucinogenic indole compounds baeocystin, norbaeocystin, bufotenein, and aruginasin synthesized in lower concentrations. These compounds are synthesized by both the fruiting body (mushroom) and mycelium of the Psilocybe fungus, though much more prolifically by the fruiting body. Psilocybin is a naturally occurring active prodrug, a compound that after ingestion is metabolized into a pharmacologically active drug). 


Psychoactive compounds in Psilocybe Mushrooms


Psilocybin's natural process of synthesis 

Contrary to popular belief, the compound responsible for the mind-altering effects of Psilocybe mushrooms is not psilocybin itself, but psilocin. Studies show that psilocin concentrations in the blood plasma of about 4-6 µg/liter or greater produce psychological effects. After ingestion the majority of psilocybin is quickly metabolized in the liver through the action of enzymes called alkaline phosphatases. These enzymes dephosphorylate psilocybin into psilocin.

As psilocybin is converted into psilocin, it undergoes a first pass effect, where its concentration is reduced before it reaches the circulatory system. Psilocin is broken down by the enzyme monoamine oxidase to produce several metabolites, including 4-hydroxyindole-3-acetaldehyde, 4-hydroxytryptophol, and 4-hydroxyindole-3-acetic acid. These metabolites are able circulate in the blood plasma. Any psilocin that isn't broken down is formed into a glucuronide, a biochemical mechanism animals use to eliminate toxic substances by linking them with glucuronic acid, which can be excreted in the urine.


Aproximately 50% of psilocybin is absorbed through the stomach and intestines. Within 24 hours, about 65% of the absorbed psilocybin is excreted in the urine, and a further 15-20% is excreted in the bile and feces. Most of the drug is eliminated this way within 48 hours, however it is still detectable in urine for ~ 7 days.


Similarity between Psilocybin and Serotonin

Psilocybin's metabolic process 

Psilocin’s molecular structure is very similar to the structure of the neurotransmitter serotonin. Psilocin imitates serotonin, and readily binds with three specific 5-hydroxytryptamine (5HT) receptors, the 5-HT, 5-HT2B and 5-HT2C receptors, with a slightly lower affinity for the 5-HT1A receptor. 


Serotonin is a key neuromodulator whose biological function is complex and multifaceted, modulating cognition, reward, learning, memory, mood, anxiety, sleep, appetite, temperature, eating behaviour, sexual behaviour, movements, gastrointestinal motility and numerous physiological processes such as vomiting and vasoconstriction. Unnatural serotonin levels are also thought to be responsible for a number of psychological conditions, including depression, addiction, and anxiety. 


The serotonergic system is composed of receptors in many regions of the brain, with the most dense concentration in the cerebral cortex. At rest, serotonin is stored within the vesicles of presynaptic neurons. When stimulated by nerve impulses, serotonin is released as a neurotransmitter into the synapse, reversibly binding to the postsynaptic receptor to induce a nerve impulse on the postsynaptic neuron

When Psilocin binds to a 5HT receptor it stimulates neurogenesis through the increased production of Glutamate and Brain derived Neutrophic Factor (BDNF). 


Glutamate is an vital neurotransmitter that accounts for over 90% of the synaptic connections in the brain, and is involved in crucial brain functions like cognition, learning, memory, and energy acquisition. 


Brain Derived Neutrophic factor is a protein that helps to stimulate and control the process of neurogenesis, it also plays a key role in long-term memory, neural development, coordination, and the deciphering of sensory input by the brain.

In addition to this antagonization of the 5HT receptor by psilocin also drastically changes the layout of brain networks and signal transmission, connecting area's of the brain that do not communicate in the "sober" or "resting" state of consciousness. This is postulated to be what is responsible for the syesnthesia (mixing of the senses) reported as an effect of psilocybin. While stimulating and enhancing connectivity in many regions of the brain, psilocybin also down regulates activity in certain networks of the brain, specifically the Default Mode Network (DMN). 

The Default Mode Network is responsible for a variety of cognitive functions including day-dreaming, self-reflection, and the ability to perceive the past, present, and future. Some studies suggest that depression is linked to an overactive DMN. The theory behind this is the possibility that a highly active DMN causes us to extensively ruminate, over-analyze, and become removed from the present moment to question the past and the future.

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