In February of 2012, the Food and Drug Administration (FDA) told makers of cholesterol-lowering statins–a relatively safe drug class that has saved thousands of lives over the past two decades–to add new side effect warnings to their labels. According to the FDA, statin labels must now include the drug’s known association with muscle injury and increased risk of diabetes. Garnering the most attention however is the drug’s association with memory loss.

Beatrice Golomb is a medical researcher at the University of California-San Diego and a major advocate of statin use and memory loss. Recently, Golomb published a paper on 171 patients using statins who reported memory problems and dementia-like symptoms. The patients attributed their symptoms to their use of the statin medications. In her paper, Golomb shows that the vast majority of the patients’ symptoms improved upon stopping the drug and many saw symptoms return upon resuming usage.

But just how serious is the issue, and do we have sufficient data to form an opinion? Prudent risk assessment is performed by weighing the drug’s benefits with its side effects. Let’s review results from a large clinical trial called JUPITER on the effects of Crestor, a statin made by Astra Zeneca. This 17,802-patient study showed that Crestor had favorable benefits by reducing the risk of a major cardiovascular event by 44%. In the evaluation, only 142 of 8,901 patients taking Crestor had a major cardiovascular event during the course of the study, compared to 252 patients taking placebo.

With regard to cognitive side effects, 69 of the almost 9,000 patients who took Crestor in this study reported a “nervous system disorder” compared to 76 in the placebo group. 515 Crestor patients reported psychiatric issues, including insomnia and depression, compared to 533 on placebo. 18 Crestor-treated subjects in the trial experienced an adverse event of “confusional state,” while 4 placebo-treated subjects experienced this adverse event. In 6 of these 18 Crestor-treated subjects, this side effect was considered serious. But while 18 patients reported a confused state the event is well below 1% of the patients (0.2% to be exact).

Looking at the results from a different perspective, around 7% of the patients in the JUPITER trial reported neurologic and psychiatric side effects while taking Crestor. That means that for every person whose confused state was caused by Crestor, another 43 had neurological or psychiatric side effects not likely attributed to the drug. The combined data tends to support the hypothesis that Crestor-induced memory loss is a rare event.

Unfortunately, the exact incidence of statin-induced memory problems is unknown, and only additional information over time will provide a better estimate. Maybe the best opinion on the matter comes from Amy Egan, Deputy Director for safety in FDA’s Division of Metabolism and Endocrinology Products who said in a statement, “The value of statins in preventing heart disease has been clearly established, and their benefit is indisputable. But they need to be taken with care and knowledge of their side effects.”