Researchers at the National Institute on Alcohol Abuse and Alcoholism have gone through every human brain-imaging study of GLP-1 drugs they could find – 37 of them – and report one reasonably consistent result: a single dose blunts the brain’s response to reward. Almost everything else is less settled than the popular account suggests. The effects are not uniform across reward processes, they differ by a person’s metabolic state, and they change over the course of treatment, becoming weaker or simply different after prolonged exposure. That matters because these drugs are now being investigated for addiction and neurodegenerative conditions on the strength of exactly this mechanism.
What the 37 studies actually measured
The review searched PubMed and Embase from inception to January 2026 for human studies using structural MRI, task-based and resting-state functional MRI, molecular imaging and neurophysiological methods. Thirty-seven met the inclusion criteria. Taken together they show GLP-1 receptor agonists engaging distributed cortical and subcortical systems rather than one localised target.
The authors single out attenuation of reward-related responsivity after acute administration as among the more consistent findings. But they are careful about the word uniform. The evidence, they write, suggests these drugs modulate reward-related processes differently rather than damping reward function across the board, with the neural effect varying according to metabolic status and underlying phenotype.
The temporal pattern is the part least likely to survive translation into a headline. Several of the included studies indicate that the central nervous system effects evolve: neural modulation is more pronounced during short-term treatment and is diminished or altered after longer exposure. A scanner session after one injection and a scanner session after nine months are, on this evidence, measuring two different things.
Why this is not the same as “it quiets food noise”
A change in a reward-region signal on a scan is a measurement of brain activity, not a measurement of what someone eats, drinks or wants. This review synthesises imaging outcomes; it does not report clinical outcomes, and it makes no claim that a given imaging finding predicts weight loss, reduced drinking or anything else a patient would notice. The step from one to the other is the step that has not been made.
The temporal finding also cuts against a common shortcut. A great deal of the public discussion of GLP-1 drugs and the brain rests on acute-dose imaging studies. If neural effects are strongest early and change later, those studies are a poor model for what months of treatment do. It is a reason to be cautious about the other direction too: our coverage of reported neuropsychiatric effects rests mostly on pharmacovigilance and cohort data, not imaging, and this review does not settle that question either.
What is not yet known
This is a systematic review, not a meta-analysis: there is no pooled effect size, because the studies are not comparable enough to pool. The authors say so directly, citing small sample sizes and methodological heterogeneity that limit direct comparison and calling for greater standardisation in future work. The paper is published online ahead of print, so page numbers and any post-review corrections are still to come. It is from a US government research institute and declares no competing interests. We read the review’s own abstract and summary of findings, not the 37 included studies.
Sources: Brucar LR, Miller KB, Volkow ND, “Central Nervous System Effects of GLP-1 Receptor Agonists: A Systematic Review of Human Neuroimaging Studies”, Neuroscience and Biobehavioral Reviews, online ahead of print 19 September 2026 (PMID 42762879). Background on this class of drugs: our GLP-1 research hub.
