The US Federal Food and Drug Administration, (FDA) is refusing to give a licence to a new weight loss drug until further clinical tests have been carried out. The FDA is worried that Contrave, a new combo medication has been thoroughly evaluated for any cardiovascular risks.

Contrave which is manufactured by pharmaceutical company Orexigen contains a combination of bupropion and naltrexone. The latter is used primarily for alcohol dependence, although it is also used for a variety of other medical disorders, including Crohn’s disease. Bupropion is an antidepressant.

The FDA decision comes after a previous committee voted last December 13 to 7 in favour of allowing Contrave to be marketed. However the FDA disagreed; the agency is worried that the benefits may not outweigh the risks.

This will obviously be a great disappointment for Orexigen who says they have carried out a lot of clinical trials, including four separate placebo trials over one year. The trials involved 3,200 obese patients possessing at least one co morbid condition. The latter includes diabetes and depression.

Orexigen says that all four trials found that more than 30% of participants lost weight (at least 5% of their body weight) by using Contrave. This last point is one of the factors by which the FDA judges the efficacy of a weight reducing drug.

Regarding the cardiovascular risks, Orexigen believes that Contrave was within the acceptable risk levels. The company is also at a loss as to why the FDA is forcing them to carry out further tests. In a letter to Orexigen, the FDA said: “Before your application can be approved, you must conduct a randomized, double-blind, placebo-controlled trial of sufficient size and duration to demonstrate that the risk of major adverse cardiovascular events in overweight and obese subjects treated with naltrexone/bupropion does not adversely affect the drug’s benefit-risk profile.”

Orexigen believes they have done this already.