This study examined whether the psychological experiences people have while taking ketamine or psilocybin—such as feeling disconnected or having spiritual insights—are actually responsible for their mental health improvements. Researchers analyzed 23 studies and found that these subjective experiences explain about 10% of ketamine’s benefits and 24% of psilocybin’s benefits. Psilocybin’s effects appear more connected to therapeutic outcomes than ketamine’s, and both drugs showed stronger connections between subjective effects and treatment success in substance use disorder compared to depression.