(Reuters) - Aquestive Therapeutics Inc said on Friday the U.S. Food and Drug Administration declined to approve its erectile dysfunction treatment and sought additional data.

The company said the comments in the FDA’s so-called complete response letter are “manageable” and that it would work with the agency for approval.

The company’s shares were down 6 percent in after-hours trading.

Aquestive’s Tadalafil oral film belongs to a class of drugs known as PDE5 inhibitors, the same class as Viagra and Eli Lilly’s Cialis.

The company informed the agency that it plans to engage an alternative supplier of the active pharmaceutical ingredient.

About 20 million men in the United States suffer from erectile dysfunction and are treated with pills such as Viagra.

Viagra has raked in blockbuster sales but is associated with side effects like headaches, blurred vision and dizziness.

“We continue to see a pathway to tentative approval before the expiry of the patents for the reference product,” Aquestive said.

Earlier this year, the company had received approval for its drug to treat seizures associated with a rare form of childhood epilepsy called Lennox-Gastaut Syndrome.