Compass Pathways released results of the largest-ever trial of psilocybin, the psychedelic substance that was highly effective as a remedy for treatment-resistant depression, on Tuesday, Nov.9.

The Phase 2b study is the largest randomized, controlled, double-blind trial of psilocybin, the psychedelic compound in magic mushrooms.

The trial was double-blind, which means neither the trial organizers nor the participants knew each patient’s treatment dose.

A total of 233 people from ten sites across North America and Europe took part in the study. Before they started, all of the individuals stopped taking antidepressants. The individuals were divided into three groups, each receiving a different amount of psilocybin in conjunction with psychological assistance.

Seventy-nine individuals were given a single 25-milligram dose, 75 a 10-milligram dose, and 79 a 1-milligram dose. According to STAT, the lowest quantity essentially served as a placebo, serving as a point of comparison for the higher-dose therapies.

Overall, 29.1% of patients in the highest dose group were in remission three weeks after treatment, compared to 7.6% of those in the control group, and more than a quarter of the patients in the 25-milligram arm were still in remission three months after treatment.

Those who got the highest dose also had a 6.6-point reduction on a clinical depression scale (the Montgomery-Asberg Depression Rating Scale) compared to those who took 1 mg. Other individuals were given a 10-milligram dose. However, there was no statistically significant difference between the 10-milligram and 1-milligram groups.

“Everyone agrees such a result hasn’t been seen before in depression research, so we’re incredibly happy with that result,” said Lars Christian Wilde, co-founder and president of Compass.

Boris Heifets, a Stanford neuroscience researcher who studies psychedelics but was not involved in the study, concurred that the findings are “super promising.” “We’re still missing a lot of the detailed data,” he added, but the summary results are “pretty good news.”

According to Compass’ study, the effectiveness of psilocybin at three weeks is nearly equivalent to the effects of ketamine at one day, according to a smaller 2013 study, implying that the benefits of psilocybin hold up well over time.

The company’s results, which were not peer-reviewed or published in a medical journal, included side effects data suggesting a limited number of significant adverse events.

Overall, 12 patients, five in the 25-milligram group and six in the 10-milligram group suffered treatment-emergent significant adverse events, including suicidal conduct and self-injury. In the 1-milligram group, just one patient had an important adverse event.

In a Tuesday morning investor call, Guy Goodwin, Compass’ chief medical officer, said, “The suicidal behaviors were reported at least one month after the administration of treatment. And they occurred in patients who were essentially non-responding,” Suicidal ideation was detected early in treatment in at least one case, he added.

According to Wilde, the differences between treatment arms aren’t statistically significant, indicating that suicidal behavior and ideation are prevalent among depressed patients.

Compass Pathways’ treatment has been designated as a breakthrough therapy by the US Food and Drug Administration, which means the drug licensing process will be accelerated if trials continue to demonstrate excellent results.

Compass is planning to start a Phase 3 trial next year; present data indicate that a 25-milligram dose will be used, but Wilde said that choice would be taken after discussions with regulators, reported Live Science.

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