The expected green light from Brussels in the next few weeks would mean that the French giant Sanofi-Aventis could begin marketing the treatment, called rimonabant but branded as Acomplia, later this summer. It is the first of a new generation of drugs set to hit the market in the next few years that could transform obesity, still a small market, into a gold mine for the pharmaceutical industry.
Pfizer, Bayer, Eli Lilly and Merck are developing treatments similar to Acomplia, though they are further behind. Sanofi plans to launch Acomplia first in the UK, Germany, Ireland and Scandinavia.
The timing is auspicious. Governments in Europe and the US have put obesity and its associated conditions, including Type 2 diabetes, at the top of their public health agendas. The Department of Health says that more than half of all British adults - 24 million people - are either overweight or obese. In America, obesity and its complications are estimated to cost the country $70bn (£37bn) annually, according to Scrip Reports.
Gbola Amusa, an analyst with research firm Sanford C Bernstein, said that Acomplia could achieve $4.1bn in annual sales by 2010, in part because it has been shown in clinical trials not only to trim fat but to increase levels of good cholesterol and control diabetes.
"In the blue sky scenario, this could become the world's best- selling drug as the indication is so broad," he said. "It has a path to revenues that we rarely ever see from a pharma product."
The treatment is the first in a new class of drugs called canna- binoid CB-1 blockers, which suppress appetite by blocking the receptor in the brain responsible for hunger pangs, which can be stimulated by marijuana.
The Committee for Medicinal Products for Human Use (CMPH), an advisory group to the European medical regulator EMEA, recommended on 28 April that Acomplia be approved for obese patients, as well as for overweight people with Type 2 diabetes or dyslipidemia, both of which are conditions that governments usually fund. The EC follows CMPH recommendations in nearly all cases.
"We are 99.9 per cent sure of approval," a Sanofi spokesman said.
Only two prescription weight-loss drugs are on the market, and neither has had much success. Abbott's Meridia is an appetite suppressant that produces an artificial sense of being sated, but it also causes hypertension. Roche's Xenical works by blocking the body's ability to absorb fat. However, any fat ingested must be passed out of the body through the bowels, which many patients find uncomfortable.
Neither can be prescribed for any indications beyond weight loss. "It's not being obese that kills you, it's the side-effects that come along with it," said Dr Julian Mercer of the Rowett Institute. "Addressing associated risk factors is a novel aspect."
Approval in America, the world's biggest drugs market, is crucial. The US industry regulator gave an "approvable letter" for Acomplia in February, asking for more time and information before it gave its final decision. Sanofi's head of research and development, Gérard Le Fur, said at the company's annual general meeting in Paris last week that he expects to get US approval by the end of the year.
The indications for which it is approved are also important. Neither Orlistat nor Meridia qualify for reimbursement with US insurers. If the label includes Type 2 diabetes and dyslipidemia, as is expected for Europe, the chances that insurers will pay for it are much greater.