Meta-correlation of the effect of ketamine and psilocybin induced subjective effects on therapeutic outcome

There is some evidence that the subjective effects of ketamine and other psychedelics like psilocybin are crucial for their therapeutic outcomes, such as treatment of depression or substance use disorder (SUD). We performed a meta-analysis and systematic review on the correlation of subjective symptoms and dissociation versus ketamine-induced therapeutic outcomes in patients with depression or SUD. A similar analysis was conducted for psilocybin-induced therapeutic improvement. We retrieved 23 papers studying ketamine (21 on depression, 2 on SUD) in 471 patients and 8 papers studying psilocybin (6 on depression, 2 on SUD) in 183 patients. Our study demonstrated a modest role for subjective effects mediating therapeutic outcomes, with R²-values ranging from 5–10% for ketamine and for psilocybin the R² was 24%. A greater mediating effect for psilocybin compared to ketamine was detected, particularly when restricting the analysis to depression. Additionally there is a greater mediating effect in SUD than depression, irrespective of treatment.