UPDATE 1-FDA panel to review Arena weight loss drug Sept 16

* FDA deadline for final decision on lorcaserin is Oct. 22

* Endocrinologic and Metabolic Drugs Advisory Committee

BOSTON, June 2 (Reuters) - An advisory panel to the U.S. Food and Drug Administration will review Arena Pharmaceuticals Inc's (ARNA.O) weight loss drug lorcaserin at a meeting tentatively scheduled for Sept. 16, the company said.

The drug will be reviewed by the Endocrinologic and Metabolic Drugs Advisory Committee. The FDA often holds meetings to solicit opinions from outside scientific experts before deciding whether to approve an experimental drug.

Arena said previously that the FDA had set a deadline of Oct. 22 to come to a final decision on whether to approve lorcaserin.

A separate meeting of the advisory committee, scheduled for July 15, will review a rival weight loss drug, Qnexa, being developed by Vivus Inc (VVUS.O). The FDA has set a deadline of Oct. 28 to reach a final approval decision on Qnexa.

On Tuesday, Orexigen Therapeutics Inc (OREX.O), which is also developing a weight loss drug, Contrave, said the FDA had accepted its application to review the drug. Neither a panel meeting nor a decision date has yet been set.

Weight loss drugs are notoriously difficult to develop, and those that reach the market have often been associated with high-profile side effects.

An obesity drug developed by Sanof-Aventis SA (SASY.PA) never reached the U.S. market due to psychiatric side effects such as suicidal thoughts and depression.

A Thomson Reuters analysis forecasts 2013 sales of $418 million for lorcaserin, $357 million for Qnexa and $325 million for Contrave. (Reporting by Toni Clarke; editing by John Wallace)