A meta-analysis showed little evidence that orlistat, sibutramine or rimonabant reduced patients' weight by 5 per cent as required by NICE. Such 'modest' weight loss could mean many patients will remain significantly overweight or obese despite drug treatment, say the researchers.
The study focused on 30 randomised placebo-controlled studies into anti-obesity drugs, involving almost 20,000 patients treated for at least one year.
Analysis showed that compared with placebo, orlistat reduced weight by an average of 2.9kg, sibutramine by 4.2kg and rimonabant by 4.7kg. Because the average starting weight of participants was 100kg, the drugs often failed to reduce significant body weight.
Between 30 and 40 per cent of participants dropped out of the trials, potentially affecting perceived effectiveness of the drug.
In 2006 NICE published public guidance on obesity. Use of orlistat and sibutramine was recommended in patients with a BMI of 30 or more who fail to respond to lifestyle interventions.
According to NICE, treatment should only be continued beyond six months if the patient manages to lose 5 per cent of their body weight in that time.
Dr David Haslam, clinical director of the National Obesity Forum and Hertfordshire GP, said that average weight loss was not a useful measure. This is because patients are responders or non-responders.
'Responders will lose a lot more,' said Dr Haslam, adding that this could be as much as 10-15 per cent in some patients.
If no response is seen at six months, GPs should 'try a different medication or reinforce lifestyle modifications', he said.
The research also found that the effect of weight loss drugs on comorbidities differed.
All three lowered cholesterol and orlistat was seen to reduce incidence of obesity. Sibutramine raised BP and pulse rate.
- Average weight loss less than 5 per cent body weight.
- All three reduced cholesterol.
- Orlistat reduced diabetes.
- Sibutramine raised BP.
- Rimonabant improved glycaemic control.