Are diet pills the silver bullet for obesity?

Prescription weight loss medicines are expensive and don’t produce lasting results. Flickr/Flashstep

Welcome to part nine of The science behind weight loss, a Conversation series in which we separate the myths about dieting from the realities of exercise and nutrition. Here, Lennert Veerman, Senior Research Fellow at the University of Queensland’s School of Population Health, assesses the cost effectiveness of prescription weight-loss medicines:

If you have a problem with your health and visit a general practitioner, you might be prescribed medication to alleviate symptoms and make you feel better.

But what if your health concern is excess weight?

Pharmacology is just one of several options to treat obesity, along with lifestyle changes and the more radical option, bariatric surgery.

So how effective are weight-loss drugs? And are they worth the cost?

Last week, we published a study on the cost effectiveness of weight-loss drugs in the international science journal PLOS One. It was part of our NHMRC-funded ACE Prevention study, which examined the cost effectiveness of 150 public health interventions in Australia.

An earlier 2008 systematic review found most published studies reported anti-obesity medications were cost effective. So we were initially optimistic our review would uncover similar findings.

Prescription weight loss medications

The most commonly prescribed drugs to aid weight loss are sibutramine and orlistat.

Sibutramine (also known under trade name Reductil) belongs to a class of drugs called norepinephrine and serotonin reuptake inhibitors, which are usually prescribed to treat depression. Sibutramine is thought to aid weight loss by suppressing the appetite and increasing metabolism.

Orlistat (Xenical) is a lipase inhibitor which appears to aid weight loss by preventing the digestion and absorption of dietary fat.

Both were available in Australia and subsidised under the Pharmaceutical Benefits Schedule (PBS) until late last year, when sibutramine was withdrawn due to safety concerns.


In our study, we assumed obese patients would take orlistat or sibutramine as directed, for a period of 12 months. But trials have shown that about half the participants using sibutramine and one third of orlistat users had stopped before the end of the year.

This may have been because they experienced some common side effects, such as increased blood pressure for sibutramine and abdominal complaints for orlistat.

On average, people who started taking sibutramine lost 4.5 kg from the drug alone. For orlistat the average weight loss was 2.9 kg. But this wasn’t sustained.

The little available evidence shows that once people stopped taking the drugs, they quickly regained the weight they had lost. After about a year, they were likely to be at their original weight.

(Interestingly, the weight lost through diet and exercise interventions also came back but around four times slower, as participants gradually reverted to their old habits.)

Prescription medicines can reduce weight by 4.5kg but not for long. Ben Werdmuller von Elgg