Statins were not alone in being linked to memory loss 30 days after starting them - non-statin lipid-lowering drugs also showed the association.
Dr. Brian Strom, of Rutgers University in Newark, NJ, publishes the findings with co-authors in JAMA Internal Medicine.
A variety of lipid-lowering drugs aside from statins were also linked to memory loss, yet they have different molecular structures, which is what leads the authors to the conclusion that the detection bias - not the agents themselves - is probably what explains the "strong" association.
Starting statins was linked to more acute memory impairments compared with non-use, but this link to statins disappeared when they were compared against non-statin drugs used to lower cholesterol - because these too were associated with more memory problems.
Examples of non-statin drugs included cholestyramine, colestipol hydrochloride, colesevelam, clofibrate, gemfibrozil, fenofibrate and niacin.
"Given the heterogeneity of molecular structures" of these drugs and statins, detection bias "may be more likely" than a causal association, say the authors.
Detection bias is "caused by a higher likelihood of ascertainment of memory loss in patients receiving preventive therapies because of increased physician contact."
The results of the study reveal a nearly four-fold increase in the risk of developing acute memory loss in the 30 days immediately following the first use of a statin - as compared with non-users of lipid-lowering drugs.
The dose-response analysis also showed a statistically significant trend, the authors add.
Do all lipid-lowering drugs increase risk of acute memory loss?
The other possibility is that all lipid-lowering drugs lead to a higher risk of memory impairment - but this is less likely than the idea of detection bias because, say the authors, of the differences between these drug classes.
But "we cannot confirm this hypothesis using these data," they add.
The researchers used medical records from UK GPs, and a total of 482,543 statin users were compared with two control groups: 482,543 non-users of any lipid-lowering drugs and 26,484 users of non-statin classes of medication.
The authors note that, superficially - before testing the other associations - their results appeared to be positive overall for an association between acute memory loss and the use of statins, which would be "consistent with previously published studies."
But the previous evidence was from descriptions in case reports and case series, or from studies whose "findings have been Inconsistent." Also, studies of the long-term use of statins have found "either improved memory or no effect."
Cardiologists behind a paper designed to help with the dilemma of whether or not to start statins - purely as a primary preventive measure (as opposed to the usually simpler decision to use them in secondary prevention, after there has already been a heart attack or stroke) - issued tips for making the decision in March.