Short answer: In a small phase 1 study of people with metastatic cancer who had only partial benefit from a first group psilocybin retreat, a second group session appeared feasible and did not show serious adverse events within the study protocol. Details are available in a recent report on PubMed.
The second session used a higher starting dose of 35 mg, allowed participants to stay on antidepressants, and offered a 10 mg booster after 60 to 90 minutes if effects felt low. Thirteen participants completed the protocol; common short-lived side effects included increased blood pressure, nausea, and headache, and seven received the booster without new serious safety signals reported.
Exploratory measures suggested reductions in anxiety and depression scores shortly after dosing, with some persistence over weeks, and more participants reported a complete mystical-type experience compared with their first session. Because multiple protocol changes were made together, it is unclear which elements, if any, drove these changes.
Overall, a second group psilocybin retreat for partial responders in this context looked feasible in the study setting, but the sample was small and uncontrolled, so stronger trials are needed before drawing firm conclusions. Proceed with cautious interpretation.