This is a well-conducted study and its headline is nearly meaningless to an individual, which makes it the clearest example this site has covered of why both numbers must be printed[1]. The general problem is set out in the semaglutide and tirzepatide comparison.
Across 452,766 matched patients, epilepsy developed in 1,670 people on a GLP-1 drug and 1,886 on a DPP-4 inhibitor. That is 2.35% against 2.41%. The hazard ratio of 0.84 (95% CI 0.78–0.90) accounts for follow-up time and is correctly calculated; it will be reported as a 16% reduction in epilepsy risk.
The quality of the study and the size of its finding are separate judgments and should not be collapsed. This one is large, the associations held at one, three and five years, they were consistent across age and sex, and sensitivity analyses supported them — comparable rigor to the venous thromboembolism cohort. Semaglutide showed the strongest association at a hazard ratio of 0.68 — which rests on the same near-identical incidences and so is a larger relative figure attached to the same tiny absolute one.
Whether there is a mechanism is genuinely open. Epilepsy and metabolic disease share pathways that these drugs plausibly touch, and this is not the first neurological association to appear in observational data while trial evidence stays quiet — the same pattern described in lower odds of getting Parkinson's, no help once you have it, where prevention signals and treatment nulls came from different study designs.
The practical translation is short. Nobody should choose or avoid a diabetes drug on epilepsy grounds from this evidence, and nobody with epilepsy should expect a GLP-1 drug to do anything for it. What the study contributes is a reassurance — these drugs do not appear to raise seizure risk — which is a useful thing to have measured at this scale, in the same way the respiratory null in the respiratory adverse event review is useful.