In a study covering more than 2 million people in Britain, researchers from Nottingham University found that adverse side effects of statins, which are prescribed to people with high levels cholesterol to cut the risk of heart disease, were generally worst in the first year of treatment.
The findings, published in the British Medical Journal, are unlikely to affect the use of best-selling medicines like Pfizer's Lipitor and AstraZeneca's Crestor, but the study's authors said patients taking statins should be "proactively monitored" for side effects.
"Our study is likely to be useful for policy and planning purposes," said Julia Hippisley-Cox and Carol Coupland, the two professors who led the study. They said it may also be useful "for informing guidelines on the type and dose of statins."
Statins are among the most successful drugs of all time and have been credited with preventing millions of heart attacks and strokes. Heart disease is the biggest killer of men and women in the rich world and is also a growing health problem in developing nations.
In a commentary on the study, senior cardiologists Alawi Alsheikh-Al, of the Sheikh Khalifa Medical City in the United Arab Emirates, and Richard Karas of the Tufts University School of Medicine in the United States, said that, like any medical treatment, statins are not completely risk free, but that when used properly, their benefits outweigh their risks.
"It would be wise to interpret the present observations in the context of the confirmed cardioprotective effects of statins and remind ourselves and our patients that these drugs, although considered safe, are, like any intervention in medicine, not entirely free of adverse events," they wrote.
Coupland and Hippisley-Cox studied data from 368 general practices on 2,004,692 patients aged 30-84 years including 225,922 patients who were new statin users and had been prescribed a range of statins.
They found that for every 10,000 high risk women treated with statins, the positive impact would be around 271 fewer cases of heart disease and 8 fewer cases of oesophageal cancer.
On the other side, there would also be 74 extra patients with liver dysfunction, 23 extra patients with acute renal failure, 307 with cataracts and 39 with a muscle weakness condition called myopathy.
Similar figures were found for men except rates of myopathy were higher, they said. They noted that some of the effects might be due to better detection rates since patients taking statins are likely to consult their doctors more often.
The adverse effects were similar for all different types of statins, except for liver dysfunction, where the highest risks were found for fluvastatin, which is sold by Novartis under the brand names Lescol and Lochol.
"All of the increased risks persisted during the treatment, but were highest in the first year," they wrote.
(Editing by David Cowell)