The largest systematic review to date to address this issue suggests 
no adverse effects of statins on cognition.

In 2012, the FDA issued a safety announcement, noting that statin use 
might be associated with cognitive impairment such as memory loss or 
confusion. To evaluate this association, researchers conducted a 
systematic review and meta-analysis of 57 studies, including 19 
randomized controlled trials, in which assessments of cognition among 
statin users were reported; FDA postmarketing surveillance data also 
were analyzed.

Moderate-quality evidence suggested no excess risk for dementia or 
mild cognitive impairment, and low-quality evidence suggested no 
excess risk for Alzheimer disease. Analysis of postmarketing 
surveillance data revealed similar cognitive-related adverse-event 
reporting rates for statins (1.9 per million prescriptions) and two 
cardiovascular drugs not associated with cognitive impairment: 
losartan (1.6 per million prescriptions) and clopidogrel (1.9 per 
million prescriptions).

COMMENT

Although this systematic review was limited by the small number of 
randomized trials in which this outcome was evaluated, the data do not 
suggest excess risk for cognitive impairment with statin use. 
Nevertheless, a rare idiosyncratic effect of statins on cognition 
remains possible for individual patients, even if studies of large 
groups of people show no adverse effect on average. Indeed, in its 
safety announcement, the FDA acknowledged that it drew substantially 
from post-marketing case reports of adverse events.

Jamaluddin Moloo, MD, MPH reviewing Richardson K et al. Ann Intern Med 
2013 Nov 19.