Differences among psychedelic substances in subjective experience can be detected through quantitative linguistic analysis of online experience reports. Analyzing 2947 reports, distinct linguistic profiles emerged: MDMA reports showed high emotional intensity and cognitive process words, while Ayahuasca/DMT reports had little emotional language, few cognitive process words, increased analytical thinking language, and the closest semantic similarity to mystical experience descriptions. LSD, psilocybin, and ketamine reports differed only slightly from each other on these measures. Antidepressant reports featured more negative emotion and cognitive process words and were unlike mystical or psychedelic language. These findings may inform experimental research and clinical trials.
A meta-analysis of 29 studies found no evidence that psychoplastogens—including ketamine, LSD, psilocybin, and MDMA—elevate peripheral brain-derived neurotrophic factor (BDNF) levels in humans. The overall effect size was negligible (SMD = 0.024) and not statistically significant. This null result held across different drugs, doses, blood fractions, participant ages, and psychiatric diagnoses. Better-controlled studies showed even smaller effects. The findings suggest that peripheral BDNF may not be a useful biomarker for rapid neuroplasticity changes in humans, or that preclinical findings on psychoplastogen-induced neuroplasticity may not translate to humans. More precise methods, such as neuroimaging, are recommended for future translational research.