New research suggests some statin drugs may cause memory impairment. A team led by scientists at the University of Bristol in the UK tested two commonly prescribed statins in rats and found one, but not the other, reduced performance of working and recognition memory.

They write about their findings in a recent online issue of the journal PLOS ONE.

Statins are drugs that reduce levels of low-density lipoprotein (LDL) or “bad cholesterol” in the blood and are taken by millions of people worldwide.

Cholesterol is a range of vital fatty substances that all the cells of the body need in order to work properly. It is also an ingredient for making other vital substances.

But having too much cholesterol in the blood can lead to fatty deposits building up in arteries, which raises risk of cardiovascular diseases, such as coronary heart disease (angina and heart attack) and stroke.

Statins work by reducing the amount of cholesterol that cells produce, which forces them to get their supply from the bloodstream, thus lowering the amount circulating in arteries.

They are prescribed for healthy people at high risk from heart disease and also to prevent further problems in people who have already had a heart attack or stroke, or who have peripheral artery disease.

This new study follows others that have found links between statin use and other health problems.

For instance, earlier this year, a Canadian study published in BMJ found that some statins may increase type 2 diabetes risk, with patients taking atorvastatin (brand name Lipitor), rosuvastatin (Crestor) and simvastatin (Zocor) showing the highest risk.

And more recently, a US study published in JAMA Ophthalmology, suggested statin use may raise cataract risk.

There is also evidence that some medications can interact with lovastatin (brand names include Mevacor) and increase the risk of muscle damage.

This last point was made last year in a consumer update on statins by the US Food and Drug Administration (FDA), which also mentioned some statin users had been reporting cognitive problems, such as memory loss, forgetfulness and confusion.

In that update, the FDA said that while the value of statins in preventing heart disease has been clearly established, they would be changing the drug labels of popular statin products to reflect some of these new concerns.

For their study, the researchers tested two commonly prescribed statins, pravastatin (Pravachol) and atorvostatin (Lipitor) in rats.

The results showed pravastatin, but not atorvostatin, impaired the animals’ ability to perform simple learning and memory tasks.

They gave rats a daily dose of the statins for 18 days and tested their ability to perform a simple learning task involving finding a food reward – before, during and after treatment.

On the last day of treatment and one week after ceasing treatment, they also tested the rats’ ability to recognize a previously encountered object – this tested their recognition memory.

The results showed that over the last few days of treatment, daily medication with pravastatin tended to impair the rats’ learning. However, this effect was reversed when treatment ceased.

Also, in the recognition memory test, taking pravastatin reduced rats’ ability to discriminate new objects.

However, “no effects were observed for atorvostatin in either task,” write the authors, who conclude that “chronic treatment with pravastatin impairs working and recognition memory in rodents.”

They note that the reversibility of the cognitive impairment effect of pravastatin is similar to that reported by patients and the fact atorvostatin did not have any effect at all suggests some types of statins may be more likely to impair memory and learning than others.

Lead author Neil Marrion, professor of Neuroscience at Bristol, says:

This finding is novel and likely reflects both the anecdotal reports and FDA advice. What is most interesting is that it is not a feature of all statins.”

“However,” he adds, “in order to better understand the relationship between statin treatment and cognitive function, further studies are needed.”

A grant from the Wellcome Trust helped finance the study.