A widely used anti-obesity drug, Sibutramine, has come under the US regulatory body Food and Drug Administration (FDA) scanner while the European Medicines Evaluation Agency (EMEA) has already barred its usage with recommendations that doctors stop prescribing the drug and pharmacists told not to dispense it.

The FDA has suggested that patients with a history of high-risk diseases should avoid its use.

The drug has been in wide use in India since 1999 and after the warning, the Drug Controller General of India (DCGI) has decided to refer the matter to an expert group.

The DCGI, Surinder Singh told the Indian Express that if experts see a problem in the drug, the manufacturers would immediately told to stop its production.

According to the FDA the warning is based on the results of a study conducted on 10,000 patients. According to a preliminary analysis, patients using sibutramine experience a higher number of cardiovascular events.

The drug is widely prescribed for patients who fail to respond to a strict diet regime.

The US currently ranks the most lucrative single market for weight loss drugs, with around 68 per cent of the population either overweight or obese. The UK and other European countries follow the US in terms of overweight population. But, according to experts China, Russia, India and Brazil could soon overtake western countries in terms of percentage of obese population.

China's obesity and overweight levels, for instance are have been predicted to touch 665 to 670 million in 2015.

But for the growing numbers of obese people there are few options apart from pharmaceuticals to help shed pounds.

The US market is dominated by two prescription anti-obesity drugs, Roche's Xenical (orlistat), a lipase inhibitor, and Abbott's Meridia (sibutramine hydrochloride), an appetite suppressant.

Between them the two represent two-thirds of the $1.4 billion prescription anti-obesity market in terms of revenues.

A third class, which is only effective on a short-term basis speeds up metabolism to promote weight loss.

In the pipe line are three anti-obesity drugs from smaller US biotech companies undergoing clinical trials or awaiting FDA nod later in the year.

Qnexa, is a formulation of low dose phentermine (an appetite suppressant) and topiramate. It has completed phase 3 clinical trials and the manufacturer applied for FDA approval December 2009.

Lorcaserin, a new class of stimulant drug targets serotonin 2C receptors in the brain. Phase 3 trials of Lorcaserin have been completed and its developer Arena Pharmaceuticals applied for FDA approval in late 2009.

Contrave (bupropion SR/naltrexone SR) and Empatic (zonisamide SR/bupropion SR) are under clinical trials. Both drugs have been developed by Orexigen, and are combinations of two existing drugs formulated for weight-loss.