Arena Pharmaceuticals Inc. reported a smaller fourth-quarter loss Monday, but said it is still waiting for federal regulators to make a decision about the status of its weight loss drug Belviq.

The Food and Drug Administration approved Belviq on June 27, but the drug has not gone on sale yet. The Drug Enforcement Administration is proposing that Belviq be classified as a Schedule IV controlled substance, which means it has a relatively low potential for abuse. Arena and its partner Eisai Co. can't start marketing Belviq until that classification is approved. It's not clear when that will happen.

Arena said a public comment period on the DEA's proposed classification ended in mid-January. The company originally hoped for a final decision last year.

Shares of Arena Pharmaceuticals lost 35 cents, or 4.2 percent, to $7.99 in morning trading.

Belviq has two main components: phentermine, a stimulant that suppresses the appetite and which has long been used for short-term weight loss, and topiramate, which is used to treat seizures. Phentermine was part of the fen-phen diet drug cocktail, which became a popular weight-loss prescription in the 1990s. The DEA classifies it as a Schedule IV controlled substance. Topiramate is not a controlled substance.

Arena said it lost $21.3 million in the fourth quarter, compared to $23.7 million in the fourth quarter of 2011. Arena sold more than 70 million new shares of stock in 2012, so its per-share loss decreased to 10 cents from 16 cents. Revenue fell to $1.9 million from $2.1 million

Analysts were expecting a smaller loss of 2 cents per share and $3.1 million in revenue, according to FactSet.

Belviq was the first long-term weight loss drug approved by the FDA in more than a decade. A competing drug, Qsymia, was approved a few weeks after Belviq. Vivus Inc. started selling Qsymia in September, and Wall Street has been disappointed with early sales.

Arena said it lost $88.3 million, or 45 cents per share, in 2012. The company took a loss of $111.5 million, or 80 cents per share, in 2011. Revenue more than doubled to $27.6 million from $12.7 million.

The company expects to spend $70 million to $78 million on research and development in 2013, up from $54.1 million in 2012 and $58.7 million in 2011. It expects about $65 million in milestone payments from Eisai in 2013, including payments connected to the DEA's final decision on Belviq. Arena will also get royalty payments on sales of the drug.