A number of patients with diabetes are being given a drug that could kill them, according to researchers in North Carolina.

A study on metformin, also sold as Glucophage and Novo-Metformin, says nearly one in four patients could experience dangerous side effects.

The study is published in the most current issue of the Journal of the American Medical Association.

Metformin helps the body use insulin and is one of the most common drugs used to treat Type II diabetes, sometimes linked to obesity and called "adult-onset" or "non-insulin dependent" diabetes.

There are at least 1.2 million Canadians with diabetes according to Health Canada. More than 90 per cent are Type II.

Metformin can cause a side-effect called lactic acidosis, a buildup of lactic acid in the blood that is fatal in half of all cases. The label says it shouldn't be used by patients with kidney disease or by those taking heart medication.

A study of metformin patients by the University of North Carolina in Chapel Hill found a quarter met that criteria. Fortunately, none of the patients developed lactic acidosis.

"It is difficult to determine whether clinicians are aware they are prescribing metformin against a black-box warning," wrote the researchers. "Black-box" refers to the highlighted cautionary information on labels of drugs that have serious side effects.

The Canadian Medical Association's guide to prescription drugs lists special precautions for metformin. Metformin is not recommended if you:

• have impaired kidney or liver function
• have heart failure
• are a heavy drinker
• are pregnant
• are breast-feeding
• are over 60

Common reactions are loss of appetite, nausea and vomiting and a metallic taste in the mouth.

Lead researcher Cheryl Horlen says several recent European studies have found similar rates of inappropriate use.

Recent studies by Harvard Medical School and Public Citizen Health Research Group say doctors don't pay close enough attention to drug warning labels.