Researchers hypothesize that the disruption of DMN activity may be a key mechanism accounting for psychedelics’ therapeutic effects in mental illness. The DMN is a group of structures that includes the posterior cingulate cortex, the medial prefrontal cortex, the angular gyrus, and other cortical areas that are active when an individual is not engaged in a particular mental task (for example, during mind wandering). It is thought to underlie introspection and to serve as an “orchestrator” of global brain function.13 Theoretically, then, by temporarily disrupting the neural circuits responsible for maintaining ingrained, negative thought and behavioral patterns, as observed in patients with depression or SUDs, psychedelics can help patients develop greater emotional and cognitive flexibility and identify new ways to view the world and to solve problems.
Evaluating psychedelics as therapeutic agents
The renaissance of research into psychedelics as therapeutic agents during the last 2 decades has produced some promising preliminary findings. In 2020, the American Psychiatric Association’s Work Group on Biomarkers and Novel Treatments published a review of the best evidence on the topic.14 Psilocybin is the most studied drug because compared with LSD, it carries less of a stigma and has a shorter duration of action. Psilocybin has been studied as a potential treatment for several psychiatric disorders, including terminal illness–related depression and anxiety, and SUDs.
Griffiths et al.15 In a double-blind randomized crossover study at Johns Hopkins School of Medicine, Griffiths et al15 administered a high dose (22 or 30 mg/70 kg) and a very low, placebo-like dose (1 or 3 mg/70 kg) of psilocybin at 2 separate sessions to 51 patients with terminal cancer and associated depressive and anxiety disorders. After 5 weeks, the participants assigned to one condition crossed over to the other condition. High-dose psilocybin had a significant effect on depression and anxiety symptoms within 5 weeks that persisted over 6 months of follow-up. At 6 months, 78% of participants experienced a response in depressive symptoms (≥50% decrease in GRID-Hamilton Depression Rating Scale [HAM-D-17] baseline scores) and 65% remitted (GRID-HAM-D-17 score ≤7). At 6 months, 83% of participants had a response in anxiety symptoms (≥50% decrease in Hamilton Rating Scale for Anxiety [HAM-A] baseline scores) and 57% remitted (HAM-A ≤7).
Johnson et al.16,17 In an open-label pilot study16 and ≥12-month follow-up study,17 Johnson et al administered a moderate (20 mg/70 kg) and high (30 mg/70 kg) dose of psilocybin to 15 participants enrolled in a 15-week smoking session program. The psilocybin sessions were scheduled at Weeks 5 and 7, with an optional psilocybin session at Week 13. The sessions included nondirective support from program staff, but not smoking cessation content. Relying on laboratory-verified exhaled carbon monoxide and urine cotinine measures, researchers found an 80% abstinence rate at 6 months, a 67% abstinence rate at 12 months, and a 75% abstinence rate at 2.5 years.16,17
Bogenschutz et al18 conducted a study of 10 patients who met DSM-IV criteria for alcohol dependence and had at least 2 heavy drinking days in the previous 30 days. They found that a 14-session treatment program that included 2 psilocybin-assisted psychotherapy sessions with dosages of 0.4 mg/kg resulted in a significant increase in self-reported alcohol abstinence at 4 weeks that persisted for 36 weeks.18
Although these studies were small, open-label, and had other methodologic flaws, their pilot work has led to larger-scale projects assessing psilocybin’s therapeutic potential. Psilocybin has also been studied for treatment-resistant depression and obsessive-compulsive disorder. Other clinical trials underway are investigating psilocybin for the treatment of cocaine and opioid use disorder, anorexia nervosa, and depression in Alzheimer’s disease.14 Although psilocybin is currently the best-studied psychedelic, there is some research demonstrating that LSD can also induce a persistent reduction in anxiety symptoms associated with terminal illness19 and that ayahuasca causes a rapid reduction in depressive symptoms that persists over 21 days.20
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