SAN DIEGO The Food and Drug Administration declined to approve a regulatory approval application from Arena Pharmaceuticals and Eisai for a drug to treat obesity, the two companies said Saturday.

The FDA issued a complete response letter for the drug lorcaserin, designed for weight management and weight loss in patients who are overweight or obese and have at least one co-morbid condition. The FDA issues a complete response letter when it finishes reviewing an approval application, but issues remain that preclude final approval.

The FDA told the companies that it found problems regarding tumors in the mammary glands of rats receiving the drug and issues surrounding the efficacy of the drug in some patients.

“This is an important step for us toward the FDA’s approval of lorcaserin,” Arena president and CEO Jack Lief said. “While the complete response letter provides us with recommendations from the agency, we intend to meet with the FDA to obtain further clarity on the approval path and timeline.”