Mind over matter: the microbial mindscapes of psychedelics and the gut-brain axis (2024)
Giorgia Caspani, Simon Ruffell, WaiFung Tsang, Nige Netzband, Cyrus Rohani-Shukla, Jonathan Swann & Wilfred Jefferies
This comprehensive review suggests that psychedelics such as ayahuasca might affect — and be affected by — the make-up of a person’s gut microbiome. This opens the possibility for individualised treatments based on someone’s “microbial fingerprint”.
We each have around 40 trillion microbes living in and around us—more than the number of human cells in our bodies. Most of these microbes are found in the gut and are connected to our nervous system through the 'gut-brain axis,' a complex, bidirectional system that significantly influences our mental and physical health.
Psychedelics appear to cause changes in the gut, which could impact the psychedelic experience and therapeutic outcomes. However, it is not yet clear whether the changes in the gut cause changes in the psychedelic experience, vice versa, both, or neither.
Psychedelics have an effect on the gut microbiome, with serotonin playing a crucial role in these effects. Serotonin is important in the gut because:
Serotonin receptors are found throughout the gut.
SSRIs, a type of antidepressant, are antimicrobial and can alter the composition of the gut microbiota.
Serotonin molecules cause changes in the function of specific areas of the gut.
Serotonin production is influenced by changes in the gut.
Early evidence also suggests that some chemical compounds found in psychedelics have anti-microbial, anti-viral, and even mild antibiotic effects. Ayahuasca is a particularly interesting case, as analysis of the ayahuasca vine (B. caapi) shows that it inhibits the growth of antibiotic-resistant bacteria. Additionally, ayahuasca has purgative effects (causing vomiting and diarrhoea), which might result from its serotonergic effects on the gut microbiome.
The gut microbiome also affects how a person responds to psychedelics. The composition of gut microbes influences how compounds are metabolized in the body. In addition to serotonin, this effect may be linked to the immune system, hormones, neuroplasticity, and the connectivity of brain networks.
In clinical practice, these findings suggest potential implications for personalized medicine. Everyone’s gut microbiome is unique, like a 'microbial fingerprint.' In theory, we could predict how a person will respond to psychedelic treatment based on their gut microbiome. We might also be able to target the microbiome to enhance the effectiveness of psychedelic therapy, personalising the treatment by adjusting the substances used, dosage, route of administration, and accompanying diet according to an individual’s gut microbiome. However, these findings are speculative, and more research is needed to confirm them.