Systematic review · 2026
Review: how psychedelics and ketamine affect thinking skills in the days and weeks after
- Original title
- Subacute and long-term changes in cognitive functioning after administration of classic psychedelics, MDMA and ketamine: A systematic review of clinical and preclinical evidence.
- Authors
- Kelly C, Cooley BJ, Zeng L, et al.
- Journal
- Neuroscience and biobehavioral reviews, 2026
- Molecules
- Psilocybin, Ketamine, LSD, DMT, MDMA
- Conditions
- Healthy volunteers, Other
- Evidence grade
- Low
- Source
- Read the original paper
The question
Do classic psychedelics, MDMA and ketamine change how people think in the days, weeks or months after a dose, rather than only during the drug experience?
What they did
Researchers searched four large research databases (MEDLINE, EMBASE, APA PsycInfo and Web of Science) for human and animal studies measuring cognition at least one day after a psychedelic or ketamine was given. Cognition here means things like executive function (planning and mental flexibility), attention and decision-making. Sixty-seven articles met their criteria: 47 in people and 20 in animals. They also formally assessed how likely each study was to be biased.
What they found
Psilocybin had the most consistent signal of improved thinking in the days and longer term, especially cognitive flexibility (switching between mental tasks) and attention. Ketamine showed improvements across several cognitive areas, but results varied a lot between studies. LSD and DMT showed no consistent short-term-after effects, and MDMA was linked to temporary declines in cognition that resolved within days. Improvements showed up more often in people with psychiatric conditions than in healthy participants, which the authors suggest may mean existing deficits were being restored rather than normal thinking being boosted.
The fine print
This is a narrative synthesis, not a pooled statistical analysis, so no overall effect size is given. The included studies had selective outcome reporting, poorly reported missing data and inadequate methodological detail, which the authors say limits confidence. Animal studies were mixed in with human ones, the total number of participants is not reported, and this summary is based on the abstract only.
What it means
There are early hints that some of these drugs are followed by measurable changes in thinking skills beyond the acute experience, but the underlying studies are too inconsistent and too poorly reported to say how large or lasting any change is.
Evidence grade: Low. A systematic review without pooled statistics that mixes human and animal studies, and the authors themselves flag selective reporting and poor methodological detail in the included research.
This summary is based on the study’s published abstract.