The Canadian and American researchers, led by Dr. Mahyar Etminan, collected data from 9 studies on the use of nonsteroidal anti-inflammatory drugs in 15,834 people. They conducted two separate analyses: One explored the risk of Alzheimer disease in users of all types of drugs in the class, whereas the second explored that risk among people who used only aspirin. The investigators were interested in studying the effect of aspirin as some studies have suggested that its mechanism of action differs from that of other drugs in the same general class.

The pooled relative risk of Alzheimer disease among current users of nonsteroidal anti-inflammatory drugs was 0.72 (95% CI = 0.56-0.94), while the pooled relative risk for aspirin users was 0.87 (95% CI = 0.70-1.07). The lack of a statistically significant benefit with aspirin use may be related to the smaller number of subjects who took aspirin. It is also possible that aspirin may be less beneficial than other drugs in the same class.

One explanation for the finding may be that aspirin has less of an anti-inflammatory effect at the lower doses commonly prescribed for the prevention of cardiovascular events than at the higher doses typically used with other nonsteroidal anti-inflammatory drugs. Etminan noted that open questions for these agents include appropriate dosage, duration, and risk-benefit ratios. Future prospective studies may help answer these questions.