Statins lower cholesterol
GPs should think more carefully about prescribing cholesterol-busting drugs say researchers who highlighted a range of "unintended" side effects.
Some doses and types of statins are linked with a greater risk of adverse effects, including liver problems and kidney failure, the UK research showed.
Doctors will have access to a computer program based on the findings to help spot those most at risk.
Millions of UK adults take the drugs to reduce heart attack and stroke risk.
The researchers, from the University of Nottingham, stressed that for many people the benefits of statins outweighed any adverse effects, but the findings would help weigh up the pros and cons in each patient.
There are plans to prescribe statins on the NHS in around one in four adults aged over 40.
The Department of Health had predicted prescriptions for the drugs would rise by 30% a year, as GPs find more and more people eligible.
At the moment, anyone judged to have a one in five or greater risk of developing cardiovascular disease over 10 years is advised to take a statin.
But there has been much debate over side effects and the latest research set out to confirm where the problems may lie in a "real life" population.
Researchers looked at data from more than two million 30-84 year-olds from GP practices in England and Wales over a six-year period.
Adverse effects identified in the study, published in the British Medical Journal, include liver problems, acute kidney failure, muscle weakness and cataracts.
For kidney failure and liver dysfunction, higher doses of the drugs seemed to be associated with greater risk.
Risks of side-effects were greatest in the first year of use.
On the positive side, the analysis also showed no significant association between the use of statins and the risk of Parkinson's disease, rheumatoid arthritis, blood clot, dementia, osteoporotic fracture, or many cancers including gastric, colon, lung, renal, breast or prostate.
RISKS OF STATINS
For every 10,000 women treated with statins:
271 fewer cases of cardiovascular disease
8 fewer cases of oesophageal cancer
23 extra patients with acute kidney failure
73 extra patients with liver dysfunction
307 extra patients with cataracts
39 extra patients with muscle weakness
Figures were similar for men, except there would be 110 extra cases of muscle weakness
Study leader Professor Julia Hippisley-Cox, who also works as a GP, said the computer programme they had devised meant GPs could work out which patients were most at risk of side-effects and whether their risk of heart disease was high enough to warrant them taking statins.
"People should be able to make an informed choice," she said.
"There are risks and benefits to all medicines, but if you have a patient at higher risk than average of something serious you might want to warn them to come back if they have problems."
June Davison, cardiac nurse at the British Heart Foundation, said: "We already know that a small number of people taking statins experience unwanted side effects.
"However, for people with, or at high risk of heart disease, the benefits of statins far outweigh this risk.
"Anybody experiencing side effects while taking statins should speak to their doctor."