Psychedelics are believed to affect the levels and activity of certain neurotransmitters. Classic psychedelics, like LSD and psilocybin, bind to serotonin receptors in the brain, leading to changes in mood, thought, perception, and behavior. In the case of ketamine, the primary action appears to be on glutamate receptors, which has the knock-on effect of increasing the amount of brain-derived neurotrophic factor (BDNF). This protein encourages the growth and repair of neurons and synapses.