(Reuters) - A panel of independent advisers to the U.S. Food and Drug Administration overwhelmingly concluded on Wednesday that there is not enough evidence to support approval of Intellipharmaceutics International Inc’s long-acting opioid painkiller.

Long-acting opioids contain high doses of narcotics designed to be released over time. If crushed pills are snorted or injected, they release their full dose all at once, making them dangerous and valuable for addicts.

Toronto-based Intellipharma’s painkiller, Rexista, is designed as a unique abuse-deterrent version of Purdue Pharma’s oft-abused blockbuster OxyContin, which already has tamper-resistant properties.

Most notably, the drug contains a blue dye that is emitted if the tablet is manipulated, which could help identify abusers, and a nasal irritant aimed at discouraging misuse.

The company is seeking a label that shows its version reduces the likelihood of intravenous abuse, which is most popular with addicts. But it is also designed to better deter oral and intranasal abuse.

While Intellipharma conducted lab tests to evaluate the abuse potential of its formulation, most panelists took issue with the fact that the company had not conducted any human studies to prove its product works as intended.

Since Rexista was shown to be bioequivalent and therefore interchangeable with OxyContin in lab studies, Intellipharma believed that conducting human studies prior to applying for approval was not imperative.

However, panelists voted 22-1 against approving the drug, largely echoing the analysis of FDA scientists who raised concerns about the lack of abuse-liability data in a preliminary review on Monday.

Intellipharma also did not conduct any safety studies on the blue dye in its product, and panelists raised questions about the ingredient’s potential toxicity and whether the bright color would attract addicts instead of deterring them.

The discussion also highlighted the inherent weakness in developing abuse-deterrant opioids. Even if Rexista were to be approved, addicts could just as easily move on to another opioid, panelists said.

The FDA usually follows the recommendations of its panel, but is not obligated to do so. The regulator is expected to decide on Rexista’s approval by Sept. 25.

Opioids are considered the gold standard in treating pain that persists despite other forms of therapy, but the rising wave of abuse is taking a toll on the U.S. healthcare system.

Health regulators have implemented a slew of measures to limit their supply, in particular requiring drugmakers to prove their painkillers deter abuse.