Herbal diet drug 'is heart risk'

The supplement is supposed to aid slimming

Slimmers have been warned against using a popular herbal remedy to help them lose weight.

Doctors in the United States say Metabolife 356 can have a potentially lethal effect on the heart.

Writing in the Journal of the American Medical Association, doctors urged people to avoid taking the product until further research is carried out.

However, the manufacturers have rejected the claims saying studies show Metabolife 356 is safe to use.

David Cohen, national science counsel for Metabolife International, said: "Metabolife is very safe when used as recommended."

Curb appetite

Metabolife 356 is designed to promote weight loss by curbing appetite and increasing energy levels.

Professor Brian McBride and colleagues from the University of Connecticut School of Pharmacy based their findings on a study involving 15 healthy people with an average age of 27.

Metabolife is very safe when used as recommended David Cohen, Metabolife International

The volunteers were either given a Metabolife 356 pill or a dummy pill.

The researchers recorded their blood pressure and corrected QT interval (QTc), an important measurement of heart activity.

QTc measures time intervals between the electrical impulses that cause the heart to contract. A longer QTc interval can increase the risk of developing abnormal heart rhythms.

They found that 53% of participants had QTc interval increases of at least 30 milliseconds while taking Metabolife 356. It also raised blood pressure.

In Europe, this is at the threshold recognised as life-threatening. According to EU regulators, it can trigger a potentially fatal irregular heart beat known as torsade de pointes.

"Consumers are drawn to herbal preparations because of their non-prescription status, direct-to-consumer advertising, and the perception that natural products are innately safe," said Professor McBride.

"Unfortunately, the perception of safety may be the result of a lack of data."

The researchers said further study was needed to identify which ingredients were causing the problem. Metabolife 356 contains 19 separate ingredients, including ephedra and caffeine.

Ephedra is about to be banned in the US amid fears it can increase blood pressure and may trigger heart attacks and strokes.

"Since the actual ingredient or ingredients in Metabolife 356 responsible for these findings are not known, patients should be instructed to avoid this and similar dietary supplements until more information is known about their safety," said Dr McBride.

However, Mr Cohen criticised the study.

"The study data is inconsistent with prior studies which have measured this exact same interval," he told BBC News Online.

He said other studies in peer reviewed journals had shown that the product was safe when used as directed.