Arena Pharmaceuticals (NASDAQ:ARNA) released its first-quarter results after the market closed today and, according to Yahoo! Finance, shares are down significantly in after-hours trading. So what exactly are investors concerned about?

Regulatory roadblocks
Arena's flagship drug, the obesity treatment Belviq, gained FDA approval last June, but the company is still waiting for the DEA to complete scheduling before it can launch the product in the U.S. with its marketing partner Eisai. Investors are certainly anxious for this drug to finally reach the market, but the glaring issue in the press release actually concerns a regulatory roadblock on the other side of the Atlantic.

Back in January, Arena received the Day 180 List of Outstanding Issues from the European Medicines Agency's CHMP, which functions in a similar role as America's FDA. The committee had concerns about Belviq's potential safety risks, but they invited Arena to offer a written and oral defense of the drug before a final opinion was formed.

It looks as though Arena's response was unsatisfactory. According to the company's press release, "The CHMP's view is that certain major objections remain outstanding that preclude a recommendation for approval of the BELVIQ MAA at the present time." As a result, Arena is withdrawing its application, and will have to go back to the drawing board as it figures out how it can potentially reapply for EU approval.

Investors have already seen the EU be tough on obesity drugs recently, and while this is a blow to Arena's global strategy, the main focus continues to be on Belviq's U.S. launch. The Q1 press release did not provide an update on DEA scheduling for Belviq or a prospective timeline for the drug's launch. Therefore, the details provided in the earnings call, and a thorough examination of the financials in its 10-Q, are crucial to fully understanding the impact of this quarter's results. However, it's clear that investors are impatiently awaiting Belviq's launch -- and the chance to analyze the drug's initial sales data.