Classic Psychedelics

Classic psychedelics are grouped together because they all work on serotonin 2A receptors in the brain and central nervous system. Some studies suggest these compounds decrease blood flow to certain brain regions, including the default-mode network, a group of brain regions associated with higher-order metacognition, the construction of the ego, and conceptions of the self.

While conditions like depression and anxiety can reduce functional connectivity between certain brain regions, some research suggests that classic psychedelics can help temporarily rewire the brain and promote neuroplasticity by increasing and strengthening those connections. Several of these substances, including ayahuasca and mescaline, are naturally occurring and have been used as medicines and in spiritual practices for millennia.

Typical Effects of Classic Psychedelics

While they are active in the body, classic psychedelics can bring about visual and auditory distortions or changes; hypersensitivity to touch, light, and sound; an altered or slowed perception of time; synesthesia; and, in rare cases, hallucinations. Classic psychedelics are also associated with mystical-type or spiritual experiences, often marked by a sense of oneness or unity, or a dissolution of ego. These substances can also prompt uncomfortable and even terrifying experiences, including powerful negative emotions, confusion, paranoia, delusions, and dissociation. 

Potential Risks and Benefits of Classic Psychedelics

Classic psychedelics can provide health benefits, especially when used in therapeutic contexts, and can afford meaningful personal, philosophical, or spiritual insights. As a class, they have low-abuse liability—meaning they are virtually nonaddictive—and they have very low organic toxicity (e.g., to the brain or liver). Still, they are not without risks. People under their influence may act in ways harmful to themselves or others, which can lead to injuries or even fatalities. Sometimes the experience can lead to confusion, disturbed mood, or, in rare cases, psychosis that persists after the trip ends.

Non-Classic Psychedelics

This category includes substances whose effect profiles overlap with those of the classic psychedelics but that don’t interact as prominently, or at all, with serotonin 2A receptors in the brain. Instead, these psychedelics interact with other neurotransmitter systems, including dopamine and glutamate, and often have effects outside of the general profile of the classic psychedelics.