A local startup believes it holds a key to helping solve the nation's obesity crisis — a combination of drugs used to treat depression, alcoholism and addiction to such painkillers as opium and heroin.

Orexigen Therapeutics Inc. led a near virtual existence for the past four years, operating with just five employees and a handful of contractors.

At the direction of its venture capitalist-packed board, Orexigen issued no press releases. The firm, said Chief Executive Officer Gary Tollefson, wanted to make sure the drug worked before touting it.

San Diego's Domain Associates LLC and the Bay Area's Kleiner Perkins Caufield & Byers, Montreux Equity Partners and Scale Venture Partners are investors.

In an age where biotech companies are going public well before they have a late-stage product, Orexigen played it safe. But now the business has emerged from the shadows to compete for a chunk of the $2 billion to $5 billion market for treating obesity.

The company leased office space in December in Del Mar, completed an initial public offering in May and began the second part of the last phase of clinical trials for Contrave, its obesity drug candidate.

Contrave has so far proven safe and effective, with side effects mostly relating to nausea.

Studies have found that weight loss, as a percentage of body weight, was around 7 percent after 24 weeks on the drug — far greater than the 5 percent per year guideline required for Food and Drug Administration approval.

Tollefson, who spent 13 years at Eli Lilly & Co., said Contrave's chances of getting an FDA approval are high because the pill is a combination of two drugs that have been on the market for three decades.

Naltrexone is used to treat certain painkiller addictions and alcoholism. Buproprion is prescribed for depression.

The ingredients in Fen Phen, a diet drug combination removed from the market in the late 1990s after it was linked to heart valve damage, were also on the market for 20 years, said Leland Gershell, an analyst with Cowen & Co. in New York.

But the FDA never approved the use of flenfluramine and phentermine together. Rather, doctors began prescribing the combination off-label to treat obesity.

With more than 64 percent of adults in America overweight — 35 percent in California — the market is wide open, experts say.