Mindfulness-based programmes reduce psychological distress (anxiety and depression) in community adults who volunteer to participate, with a small to moderate effect size. The analysis of 13 randomized controlled trials with 2,371 participants from 8 countries found a standardized mean difference of -0.32, with high confidence in the result. The effect was not clearly influenced by participants' baseline distress level, gender, age, education, or dispositional mindfulness. More research is needed to understand why outcomes vary between individuals.
Placebo-controlled trials of MDMA and classical psychedelics like psilocybin, LSD, and DMT for neuropsychiatric disorders have increased, but their success depends on trial design, control conditions, and blinding. Without appropriate controls, placebo and expectation effects are hard to separate from medication effects. This paper explores the neurobiology of placebo and expectation effects and methodological considerations for selecting suitable control conditions, examining advantages and disadvantages of various options and proposing new directions to enhance trial validity and regulatory science.