Psychedelic Research Papers

This review (2024) examines the effects of classic psychedelics (e.g., LSD, psilocybin, DMT) and non-classic psychedelics (e.g., ketamine, MDMA) on neuroplasticity. Drawing on preclinical and clinical studies, it discusses molecular, structural, and functional changes induced by these agents, highlighting their potential to re-open developmental windows (hyper-plasticity) and increase nervous system sensitivity to stimuli (meta-plasticity). Translating findings to humans remains challenging, but emerging tools like PET radioligands and multimodal approaches offer promise for future research.

This robustness analysis of the ESCAPE-TRD Phase IIIb trial (n=676) investigates esketamine nasal spray versus quetiapine extended release for treatment-resistant depression (TRD). Esketamine significantly outperformed quetiapine in achieving remission at week 8 (MADRS ≤10) and maintaining relapse-free status through week 32, with hazard ratios favouring esketamine (HR: 1.658–1.711, p < 0.001).

This randomized, double-blind, psychoactive-controlled study (n=12) compared intramuscular ketamine (35-70mg/70kg) to fentanyl (50μg) in treatment-resistant OCD patients, with 10 participants completing the trial. The study found dose-dependent reductions in OCD symptoms (Y-BOCS scores) for ketamine compared to fentanyl, with effects lasting up to 168 hours, though two participants dropped out due to dissociative effects.

This meta-analysis (s=29) examines the effects of psychedelics (including ketamine and MDMA) and two other 'psychoplastogens' on peripheral BDNF levels in humans. It finds no significant changes in BDNF levels post-administration (SMD=0.024, p=0.64), regardless of drug, dose, participant age, or psychiatric condition. Studies with better-controlled designs report smaller effect sizes, and later timepoints show minimal increases in BDNF. The authors conclude that peripheral BDNF is likely not a reliable marker of rapid neuroplasticity and recommend neuroimaging or stimulation-based methods for future research.

This review (2024) highlights preclinical research from the past 15 years showing that ketamine and psychedelics trigger dendritic spine growth in cortical pyramidal neurons, enhancing neural plasticity. It compares the longitudinal effects of psychoactive drugs, emphasizing rapid-onset and sustained structural plasticity as key features of rapid-acting antidepressants, and discusses gaps in understanding and prospects for other interventions like rTMS.

This online survey (n=6,193; 2,488 microdosers) examines differences between exclusive microdosers and those who use both micro and macrodoses of psychedelics. The study finds exclusive microdosers were typically older, more likely to be female and non-Caucasian, with psilocybin (74.5%) and LSD (34.4%) being the most commonly used substances, primarily for general wellbeing (73.0%).

This retrospective analysis (n=841) of the Prehospital Tranexamic Acid Use for Traumatic Brain Injury trial evaluates the effects of ketamine in subjects with traumatic brain injury (TBI). It finds no significant difference in mortality or disability between ketamine-exposed (15.5%) and unexposed subjects, though ketamine exposure was associated with fewer instances of elevated intracranial pressure and a lower increase in TBI protein biomarkers, despite a higher likelihood of seizure activity in the ketamine group.

This meta-analysis (2024, s=31) examines the correlation between subjective effects and therapeutic outcomes for ketamine (s=23, n=471) and psilocybin (s=8, n=183) in depression and substance use disorder (SUD) treatment. It finds modest mediating effects of subjective experiences on therapeutic outcomes, with psilocybin showing a stronger mediating effect (R² = 24%) compared to ketamine (R² = 5-10%), and a greater mediating effect observed in SUD compared to depression regardless of the substance used.

This preprint open-label study (n=20) examines the effects of ketamine infusions (35mg/70kg, 6x) on biological ageing markers in individuals with depression (MDD) or PTSD. It finds reductions in epigenetic age as measured by OMICmAge, GrimAge V2, and PhenoAge biomarkers, as well as significant changes in Epigenetic Biomarker Proxies (EBPs) and surrogate protein markers following a 2-3 week treatment course. The study also reports expected decreases in depression and PTSD scores as measured by PHQ-9 and PCL-5.

This randomized, double-blind, placebo-controlled study (n=68) assesses the prosocial, entactogen effects of ketamine (35mg/70kg) in participants with treatment-resistant depression (TRD). Ketamine increased pleasure from social interactions and helping others, lasting for one week post-treatment. In a rodent experiment, ketamine-treated rats showed increased protective behaviour towards their cage mates, indicating entactogen effects.

This Phase I study evaluates the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of (2R,6R)-Hydroxynorketamine (RR-HNK) in healthy volunteers. It finds that RR-HNK has a minimal adverse event profile, no serious adverse events, and no anaesthetic or dissociative effects at all doses. The study also reports dose-proportional increases in PK parameters and promising PD outcomes, including gamma power increases in some participants and CNS exposure, supporting progression to Phase II.

This double-blind, pilot study (n=28) investigates esketamine combined with mindfulness-based intervention (MBI) for individuals with alcohol misuse problems. Esketamine enhanced psychological engagement in MBI and transiently decreased alcohol cravings, while also resulting in greater mystical experiences and dissociative states compared to placebo.

This secondary analysis of a randomized, double-blind, crossover trial (n=61) evaluates the impact of ketamine on sleep metrics in individuals with treatment-resistant depression (TRD) compared to healthy volunteers (HVs). It finds that while ketamine affects delta and alpha power during sleep, it does not significantly alter sleep macroarchitecture or mediate its antidepressant and anti-suicidal effects through sleep variables.

This open-label pilot study (n=20) investigated the safety and efficacy of intranasal ketamine for treating a single cluster headache (CH) attack. While the primary endpoint of a 50% reduction in pain intensity within 15 minutes was not met, at 30 minutes post-treatment, pain intensity was significantly reduced by 59% on an 11-point scale, with no serious adverse events reported.

This randomized controlled trial (n=116) investigated the psychological mechanisms of ketamine's antidepressant effects. Participants receiving ketamine reported significantly heightened feelings of awe compared to those receiving a placebo. Awe experiences, as measured by the Awe Experience Scale (AWE-S), mediated depression outcomes (% improvement in MADRS scores) at multiple time points (24 hours and 5, 12, 21, and 30 days) post-infusion, indicating a potential role of awe in ketamine's therapeutic efficacy for depression.

This retrospective observational cohort study (n=966 esketamine initiators, n=39,219 controls) examines factors influencing esketamine initiation and continuation for treatment-resistant depression (TRD). Initiators resided closer to treatment centres, with initiation rates decreasing significantly with distance. Factors associated with increased initiation included posttraumatic stress disorder, suicidal ideation, and male sex, while Medicaid, substance use disorder, older age, and greater distance were associated with lower initiation rates.

This single-blind placebo-controlled study (n=40) investigated the neural and behavioral effects of acute ketamine in healthy participants. Results revealed robust inter-individual variability in both neural and behavioral responses to ketamine, with data-driven individual symptom variation mapping onto distinct neural gradients. These findings emphasize the need to consider individual variation in response to ketamine and suggest potential implications for developing precise pharmacological biomarkers in psychiatry.

This pre-print open-label trial (n=117) administered intravenous ketamine in highly supportive environments to outpatients with elevated PTSD symptoms. The protocol included preparatory, integration, sensory immersion, and psychotherapy sessions, resulting in significant reductions in PTSD symptoms. The study highlights the potential of ketamine when delivered in a psychedelic therapy paradigm, suggesting it as a promising option for PTSD treatment resistant to other therapies.

This double-blind, randomized study (n=27) assessed the antidepressant effects of a novel oral prolonged-release formulation of racemic ketamine (KET01) in TRD patients as add-on therapy. Patients received either 160 mg/day or 240 mg/day KET01 or placebo for 14 days, with the primary endpoint being the change in Montgomery-Åsberg Depression Rating Scale (MADRS) scores from baseline to day 15. Results suggest a positive trend towards antidepressant efficacy with 240 mg/day KET01.

This meta-analysis (n=1100; s=14) of clinical trials on patients with depression (MDD) receiving ketamine or esketamine reveals a substantial placebo response, accounting for up to 72% of the overall treatment response. The study emphasizes the importance of considering the placebo response in clinical practice to maximize the benefit to patients.

This longitudinal study (n=71) examines five years of real-world clinical data on the use of IV low-dose ketamine alongside standard care for outpatients with depression (MDD & TRD). Results indicate a significant reduction in depressive symptoms and suicide ideation by treatment endpoint, with 55% of patients responding to treatment. Side effects were transient and mild for 78% of patients, with a dropout rate of 11%. Multivariate analysis suggests that demographic variables did not impact treatment efficacy or tolerability.

This randomized placebo-controlled trial (n=111) investigated the efficacy, safety, and tolerability of fixed low-dose oral esketamine (3x p/d 42d; 30-90mg; oral) in patients with treatment-resistant depression (TRD). Results indicate that fixed low-dose oral esketamine did not show benefit on depressive symptom severity compared to placebo, but individually titrated higher doses in the open-label extension phase demonstrated potential antidepressant properties.

This retrospective analysis (n=431) of at-home ketamine treatments (1x p/w, 50-400mg lozenges) for depression, generalized anxiety, and social anxiety found statistically significant improvements in symptoms measured via PHQ-9, GAD-7, and SAD-D-10 at all follow-up time points (1-2-3 months). Minor side effects were reported by 18.8% of patients, resolving within 24 hours, and the majority concluded treatment within ≤ 6 months. No significant differences were observed between treatment-resistant and non-resistant depression outcomes.

This systematic review (s=5) of randomized controlled trials (RCTs) compares oral psilocybin (25mg) and intranasal esketamine (56-84mg) with an oral antidepressant in adults with depression (TRD). The review showed significant depressive symptom reduction with psilocybin (Number Needed to Treat; NNT=5) and esketamine (NNT=7). Psilocybin has a Number Needed to Harm (NNH) of 5 for nausea, while esketamine induces mild side effects (NNH<10).

This systematic review & meta-analysis (2024; s=6; n=221) of randomized control trials (RCTs) on ketamine interventions for PTSD finds a small advantage for ketamine over control conditions in reducing PTSD symptoms at 24 hours post-initial infusion, but bias and heterogeneity pose concerns, indicating that blind penetration and the placebo effect might contribute to reported therapeutic effects.

This combined analysis of two cohorts (n=311) compared intravenous ketamine (KET-IV) and intranasal esketamine (ESK-NS) in the treatment of Treatment-Resistant Depression (TRD). The study found that KET-IV (n=171) had larger effect sizes and higher response rates than ESK-NS (n=140), although both significantly reduced depressive symptoms. Despite KET-IV having more reported side effects, its discontinuation rate due to adverse events was not significantly higher than ESK-NS.

This retrospective analysis (n=5061) of FAERS data on esketamine from 2019 to 2023 reveals 117 adverse reactions. In addition to known adverse events, new signals like flashback, tachyphylaxis, and autoscopy were identified. Suicidal ideation and attempts were relatively high, emphasizing the need for vigilance, while issues related to nasal administration, such as monitoring procedure errors and discomfort, were highlighted.

This Phase III, double-blind, randomized trial (n=174) evaluated the acute efficacy and safety of a 4-week course of ketamine (35-63mg/70kg) in participants with treatment-resistant depression (TRD). The study found that ketamine was more efficacious than midazolam (1.75mg/70kg) in the flexible-dose cohort (remission rate 19.6% vs 2.0%), demonstrating that adequately dosed subcutaneous racemic ketamine is both effective and safe in treating TRD over 4 weeks.

This community-based study (n=295) examined the impact of intravenous ketamine treatment on suicidality. Using growth mixture modelling, three trajectory groups were identified: one with moderate baseline scores showing gradual improvement (n=170, 57.6%), another with severe baseline scores showing no improvement (n=63, 21%), and a third with rapid improvement (n=62, 21%). Among clinical and demographic variables, only higher scores on active thoughts of death and/or plan predicted a lack of benefit from treatment for those with severe baseline CHRT-SR scores. The findings support ketamine's potential effectiveness in addressing suicidality in a proportion of patients.

This pilot randomized clinical trial (n=30) assessed the efficacy of a single subanesthetic dose of esketamine (14mg/70kg) in enhancing the effect of oral antidepressants for patients with fluctuating responses to treatment in major depressive disorder (MDD). Participants were adults with MDD experiencing fluctuating symptoms despite prior symptom relief and stabilization. The study found that response rates at 2 weeks were significantly higher in the esketamine group (66.7%) compared to the midazolam control group (6.7%), with a more substantial reduction in depression severity (MADRS score) in the esketamine group.