Cholesterol-lowering pills taken by millions of Britons may cause memory loss and depression, researchers warn.
They say not enough is known about the level of harm posed by statins, prescribed to prevent heart disease and strokes.
Leading doctors say that the drugs should only be taken by patients for whom the benefits of the drug outweigh any potential risks.
More than seven million people in Britain now take statins – as many as one in three adults over the age of 40.
They are extremely effective in lowering levels of cholesterol, the fatty substance in the blood that clogs up arteries leading to heart attacks and strokes.
Many people over the age of 45 are routinely prescribed statins by their GPs if they have slightly high blood pressure or cholesterol.
In addition low-dose pills are increasingly bought over the counter without a prescription. Although they have been proven to be extremely effective – saving up to 10,000 lives a year – researchers warn that not enough is known about their risks.
They warn statins should only be prescribed to those with heart disease, or who have suffered the condition in the past. Researchers warn that unless a patient is at high risk of suffering a heart attack or stroke, statins may cause more harm than good.
The study, published in the Cochrane Library, which reviews drug trials, also points out that the vast majority of trials have been carried out by drugs companies who may play-down any possible risks. Some patients taking statins have suffered from short-term memory loss, depression and mood swings.
Previous studies have also linked the medication to a greater risk of liver dysfunction, acute kidney failure, cataracts and muscle damage known as myopathy.