A combination of two drugs has twice the slimming power of the leading anti-obesity pill orlistat, trial results have shown.

It also has other health benefits, including lowering blood pressure and levels of harmful fatty molecules and sugar in the blood.

Researchers tested the two drugs phentermine and topiramate on almost 2,500 overweight and obese adults from 93 US centres.

Patients were split into groups who received a 56-week course of treatment with different doses of the drugs or a “dummy” placebo.

The results of the “Conquer” Phase III trial were published today in an early online edition of The Lancet medical journal.

They showed that patients taking the drugs in higher doses lost 10.2 kilograms, or 22 pounds, on average.

Overall, 70 per cent of patients in the higher dose group achieved five per cent weight loss. This compared with 21 per cent of those in the placebo group, and 62 per cent of those taking the lower dose.

In some diabetic patients, it achieved more than double the weight loss seen after up to four years treatment with orlistat.