INSYS Therapeutics Inc. said the U.S. Food and Drug Administration rejected its application to market a buprenorphine spray as a treatment for moderate-to-severe acute pain.

The company received a complete response letter from the regulator flagging potential safety concerns for the spray, which is applied under the tongue.

The Chandler, Ariz.-based company added that the letter indicated that the buprenorphine spray was statistically significantly different than placebo in providing pain relief.

The FDA's decision comes after the agency's expert panel voted in May not to recommend the approval of the therapy.

Steve Sherman, INSYS Therapeutics' senior vice president of regulatory affairs, said the company is in the process of assessing its next steps.