It looks as though Vivus' Qnexa is set to be the first prescription diet drug to reach the US market since 1999 after advisors to the Food and Drug Administration overwhelmingly recommended the pill for approval.

The agency's Endocrinologic and Metabolic Drugs Advisory Committee has voted 20-2 that the benefits of Qnexa (phentermine/topiramate) outweigh the risks. The decision to recommend approval, after a rejection in October 2010, has surprised some observers given the release earlier this week of FDA staff documents which suggested a cardiovascular outcomes trial should be needed, The staffers also expressed concern about the increased risk of birth defects, especially cleft lips.

However these concerns did not sway the committee. One panellist, Sanjay Kaul of the David Geffen School of Medicine at UCLA Cedar Sinai Medical Center, was quoted by Bloomberg as saying that "of all the obesity drugs, this one has the highest efficacy in terms of weight loss, so that shifts the balance in terms of requiring a post-approval study rather than a pre- approval study".

Indeed, the panel stressed that Vivus should conduct a post-marketing study with regards to the potential cardiovascular side effects of Qnexa. The company has also proposed a risk evaluation and mitigation strategy which includes a plan to only allow 10 US mail-order pharmacies to distribute the drug and Vivus will train the prescribers and distribute warning pamphlets if the FDA grants approval; a final decision is due around April 17.

Peter Tam, Vivus president, said "we are pleased with the panel's approval recommendation in support of the safety and efficacy of Qnexa [and] look forward to working with the FDA as they complete their evaluation". He added that "obesity is a serious medical condition, and we are committed to…providing physicians with a new medical treatment option in their battle with this public health epidemic".

The panel's recommendation pushes Vivus well ahead of Orexigen Therapeutics/Takeda's Contrave (naltrexone/bupropion) and Arena Pharmaceuticals/Eisai's lorcaserin, both of which were also rejected at the first time of asking by the FDA. The potential for Qnexa in a country where a third of adults are obese and another third are overweight is pretty clear and Vivus shares will soar when the markets open.

The last weight loss drug to be approved by the FDA was Roche's Xenical 13 years ago.