In randomized clinical trials of psychedelic drugs for psychiatric disorders, the drugs' strong subjective effects often reveal which treatment participants or raters think they received, a phenomenon called functional unblinding. A systematic review of 112 trials found that only 29.5% assessed whether blinding was maintained, yet 57.1% cited blinding as a limitation. Blinding failure exceeded 90% in psilocybin, LSD, and ayahuasca studies and 85% in MDMA trials with inert placebos. Ketamine trials rarely assessed blinding but fared better when midazolam was used as an active comparator. No control strategy consistently preserved ideal blinding, raising concerns about the validity of efficacy estimates.
A large body of evidence from clinical trials and real-world studies supports the antidepressant effects of intravenous ketamine and intranasal esketamine. Larger studies have provided reassuring safety data, including for long-term treatment. Alternative routes of administration show promise for scalability, but their efficacy relative to intravenous ketamine remains unclear. Preliminary data suggest ketamine may also be effective for bipolar disorders, personality disorders, posttraumatic stress, and obsessive-compulsive disorder. Further research is needed to optimize protocols, such as combining ketamine with other interventions. Challenges include functional unblinding, expectancy-related bias, and treatment costs.