👤 Stefan Leucht

Serotonergic psychedelics are re-emerging as therapeutic candidates across psychiatry, particularly for treatment-resistant depression. Their rapid and sustained antidepressant effects, alongside evidence for neuroplastic, dopaminergic, and glutamatergic modulation, have prompted interest in whether they could address depressive and negative symptoms in schizophrenia spectrum disorders (SSDs). This narrative review summarizes mechanistic, preclinical, and early clinical findings relevant to psychedelic use in SSDs. Schizophrenia and major depressive disorder share disturbances in dopamine, glutamate, and neuroplasticity, and both involve large-scale network abnormalities. Schizophrenia is associated with widespread dysconnectivity, mesocortical hypodopaminergia, and striatal hyperdopaminergia linked to NMDA receptor hypofunction. Depression is characterized by fronto-limbic and default mode network hyperconnectivity, mesolimbic hypodopaminergia, and reduced cortical glutamatergic tone. Depressive symptoms within SSDs may reflect an intermediate phenotype combining depressive-like hyperconnectivity with schizophrenia-related global dysconnectivity, suggesting that psychedelics' capacity to transiently increase network flexibility and recalibrate maladaptive connectivity may be clinically relevant. Preclinical studies show increased dendritic spine density, enhanced BDNF expression, restored reward sensitivity, and modulation of network dynamics after psychedelic administration. Clinically, uncontrolled exposure appears associated with increased psychosis-related presentations, whereas limited case reports suggest controlled administration may be tolerated in carefully selected, clinically stable individuals with SSDs. To date, only one early-phase trial (MDMA in schizophrenia) is ongoing, and no randomized trials have evaluated psilocybin or LSD in SSDs. Overall, psychedelics are biologically and mechanistically plausible but remain unproven for depressive and negative symptoms in SSDs, which partially overlap. Carefully designed, safety-focused early-phase studies in clinically stable patients are therefore a prerequisite for broader clinical application. Show less

Weight gain is a frequent side effect of treatment with SGAs (second-generation antipsychotics) and a leading cause for nonadherence. Several candidate genes have been identified that could influence the amount of AIWG (antipsychotic-induced weight gain). The polymorphism rs17782313 near the MC4R (human melanocortin 4 receptor gene) was strongly associated with obesity in a large scale GWAS (genome wide association study), yet previous studies investigating its impact on AIWG did not lead to a definite conclusion regarding its effect. In particular, they were all relatively short and had a naturalistic design. We therefore examined the influence of the rs17782313 polymorphism on SGA-related weight gain. Participants of a multicenter randomized, controlled, double-blind study comparing two treatment strategies in individuals with schizophrenia or schizoaffective disorder were genotyped using a rapid-cycle polymerase chain reaction. Up to 252 individuals completed the first 2 weeks (phase I), 212 the entire 8 weeks (hence 'completers'). Patients received either amisulpride or olanzapine or both consecutively. Thirty-seven had their first episode. Weight gain occurring in different genotypes was statistically compared and confounding factors were adjusted by stepwise multiple linear regression. A correction for multiple testing was included. Within 212 'completers', carriers of the C allele had a higher absolute weight gain than those homozygous for the T allele (2.6 kg vs. 1.2 kg), though this observation was not significant (P = 0.063). In the amisulpride subpopulation, this association appeared stronger and reached significance (2.5 kg vs. 0.7 kg, P = 0.043), though failed to remain significant after correction for multiple testing. A stepwise multiple linear regression showed a significant association in both the whole study population (P < 0.001) and the amisulpride subpopulation (P < 0.001). Our results indicate that the rs17782313 polymorphism might influence antipsychotic-induced weight gain and therefore confirm some of the earlier conclusions. Show less