Schizophrenia involves excessive loss of brain connections, partly due to overactive microglia that prune synapses. A genetic variant in complement component 4 (C4) is strongly linked to the disease and drives this pruning. Brain scans using a new tracer for synaptic vesicle glycoprotein 2A (SV2A) confirm lower synaptic density in the prefrontal cortex of people with schizophrenia, supporting the synaptic hypothesis. Psychedelics like LSD and psilocybin promote neuroplasticity and synaptogenesis in animal and lab studies, potentially counteracting synaptic loss and improving negative and cognitive symptoms. The authors suggest starting with microdoses in deficit schizophrenia patients, then escalating if results are positive.
Serotonergic psychedelics, which are being explored for treatment-resistant depression, might also help with depressive and negative symptoms in schizophrenia spectrum disorders (SSDs). Schizophrenia and depression share some underlying brain disturbances, including problems with dopamine, glutamate, and neuroplasticity, as well as abnormal brain network connectivity. Depressive symptoms in SSDs may combine features of both disorders, and psychedelics could potentially recalibrate maladaptive brain networks. Preclinical studies show psychedelics increase dendritic spines and BDNF and restore reward sensitivity. Clinical evidence is limited: uncontrolled psychedelic use is linked to increased psychosis, but controlled administration may be tolerated in stable individuals. Only one early-phase trial with MDMA in schizophrenia is ongoing; no randomized trials have tested psilocybin or LSD in SSDs. The authors conclude that psychedelics are biologically plausible but unproven for these symptoms.