The key finding
A comprehensive 2026 systematic review of 36 studies involving 2,852 adults found that substance use is broadly associated with impaired metacognition—our ability to monitor, evaluate, and regulate our own thinking. Cannabinoids generally reduced metacognitive accuracy and calibration, benzodiazepines impaired awareness of performance and error detection, and methamphetamine showed dose-dependent effects on how people judged their own actions. Across observational studies, cocaine, nicotine, opioid, cannabis, alcohol, and polysubstance use were linked to poorer metacognitive functioning, including diminished ability to accurately monitor one’s own mental performance and increased maladaptive beliefs about thinking itself.
What the study looked like
Researchers conducted a systematic review following PRISMA 2020 guidelines, searching four major databases from their inception through March 2026. They included 36 studies with adult participants (18 years and older) that examined the relationship between substance use and metacognitive outcomes. The pool included 16 randomized controlled trials that experimentally administered substances, 3 quasi-experimental studies, 7 cross-sectional studies comparing users to non-users, and 10 case-control studies. The researchers assessed study quality using Joanna Briggs Institute appraisal tools and synthesized findings narratively rather than statistically, given the heterogeneity across substances, study designs, and metacognitive measures. Studies measured various aspects of metacognition, including accuracy of self-performance judgments, ability to detect errors, confidence calibration, and metacognitive beliefs about one’s own thinking processes.
Why researchers think this happened
The authors propose that different substances affect metacognition through distinct neurobiological pathways. Cannabinoids may disrupt the neural networks involved in performance monitoring and self-assessment, leading to overconfidence or poor calibration between actual and perceived performance. Benzodiazepines appear to specifically interfere with error-detection mechanisms and awareness of one’s own cognitive state. The dose-dependent effects of methamphetamine on agency judgments suggest that stimulants may alter the brain’s ability to attribute actions to oneself accurately. Craving states—observed with nicotine, caffeine, and methamphetamine—may compete for cognitive resources needed for accurate self-monitoring, explaining why withdrawal periods showed particularly poor metacognitive performance. The observational findings suggest that chronic substance use may lead to persistent alterations in metacognitive functioning, possibly through accumulated neuroadaptations in prefrontal and executive control regions responsible for self-reflection and cognitive control.
How to read this carefully
This review combined studies with very different designs, populations, and outcome measures, making it difficult to draw precise conclusions about any single substance. The experimental studies showed acute effects from controlled doses in laboratory settings, which may not reflect real-world patterns of use. Observational studies face the classic correlation-versus-causation challenge: people with pre-existing metacognitive difficulties might be more likely to use substances, rather than substance use causing the impairment. Sample sizes varied considerably across the 36 included studies, and the total participant pool of 2,852 was distributed across many different substances and study types. Some studies showed mixed or domain-specific findings, suggesting metacognition isn’t uniformly affected. The review also couldn’t determine whether metacognitive impairments resolve with abstinence or represent lasting changes, as longitudinal data were limited.
What this means for everyday life
Metacognition underlies many everyday skills—recognizing when you’ve made a mistake, knowing when you don’t know something, accurately judging your own readiness for a test or task, and catching yourself before acting on impulse. This research suggests that substance use may quietly undermine these self-monitoring abilities without users realizing it, creating a circular problem: the very tools you’d use to notice impaired judgment may themselves be impaired. For people who use substances recreationally, this might mean being more cautious about situations requiring accurate self-assessment—like deciding whether you’re fit to drive or make important decisions. For those supporting someone with substance use concerns, recognizing that metacognitive difficulties aren’t simply “denial” but may reflect genuine impairment in self-monitoring could foster more compassionate and effective approaches. The findings also highlight why interventions that strengthen metacognitive skills—teaching people to more accurately monitor their own thoughts and behaviors—might be valuable components of substance use treatment programs.