BackgroundIn addition to the clear cardiovascular benefit, there has been renewed interest in the potential of statins in the prevention of cognitive impairment and dementia in older adults. However, whether ongoing statin use can delay cognitive decline or dementia progression in those with established Alzheimer dementia, is unclear.MethodsUsing data from NILVAD, we analysed the association between ongoing statin use and cognitive decline (Alzheimer Disease Assessment Scale-Cognitive Subsection [ADAS-Cog])/dementia progression (Clinical Dementia Rating Scale [CDR-Sb]/Disability Assessment for Dementia [DAD]) over 18 months in older adults with mild-moderate AD. Additionally, we assessed the association between ongoing statin use and adverse events in mild-moderate AD.ResultsOver one-third (34.9%) of 510 older adults with mild-moderate AD (aged: 72.9 years; 61.9% female) used a statin for the 18-month study duration. Statin use was not associated with the rate of cognitive decline (β: -0.67; 95% CI: -1.71, 0.36, p = 0.20) or dementia progression (β: -0.34; 95% CI -0.71, 0.02; p = 0.07 for CDR-Sb/ β: -2.00; -5.70, 1.70; p = 0.29 for DAD). Further, ongoing statin use was not associated with adverse events, serious adverse events, unscheduled GP visits, or unscheduled hospitalisation.ConclusionOngoing statin use was not associated with cognitive decline or dementia progression in mild-moderate AD. Similarly, use was not associated with adverse events including abnormal liver function tests or falls. Whilst safe in those with AD, the current results suggest ongoing statin use does not delay cognitive decline or clinical progression in established AD.