Background Epidemiologic evidence suggests that nonsteroidal anti‐inflammatory drugs (NSAIDs) delay onset of Alzheimer's dementia (AD), but randomized trials show no benefit from NSAIDs in patients with symptomatic AD. The Alzheimer's Disease Anti‐inflammatory Prevention Trial (ADAPT) randomized 2528 elderly persons to naproxen or celecoxib versus placebo for 2 years (standard deviation = 11 months) before treatments were terminated. During the treatment interval, 32 cases of AD revealed increased rates in both NSAID‐assigned groups. Methods We continued the double‐masked ADAPT protocol for 2 additional years to investigate incidence of AD (primary outcome). We then collected cerebrospinal fluid (CSF) from 117 volunteer participants to assess their ratio of CSF tau to Aβ 1‐42. Results Including 40 new events observed during follow‐up of 2071 randomized individuals (92% of participants at treatment cessation), there were 72 AD cases. Overall, NSAID‐related harm was no longer evident, but secondary analyses showed that increased risk remained notable in the first 2.5 years of observations, especially in 54 persons enrolled with cognitive impairment––no dementia (CIND). These same analyses showed later reduction in AD incidence among asymptomatic enrollees who were given naproxen. CSF biomarker assays suggested that the latter result reflected reduced Alzheimer‐type neurodegeneration. Conclusions These data suggest a revision of the original ADAPT hypothesis that NSAIDs reduce AD risk, as follows: NSAIDs have an adverse effect in later stages of AD pathogenesis, whereas asymptomatic individuals treated with conventional NSAIDs such as naproxen experience reduced AD incidence, but only after 2 to 3 years. Thus, treatment effects differ at various stages of disease. This hypothesis is consistent with data from both trials and epidemiological studies.

Extended results of the Alzheimer's disease anti‐inflammatory prevention trial