HAYWARD, Calif. — Impax Laboratories Inc. has received approval from the Food and Drug Administration for guanfacine extended-release tablets, a treatment for attention deficit hyperactivity disorder (ADHD).

Impax said late Wednesday that its guanfacine ER product, a generic version of Intuniv from Shire, comes in strengths of 1 mg, 2 mg, 3 mg and 4 mg.

“Since the resolution of the warning letter at the Hayward facility in early September, the FDA has approved three generic products from this facility in the last five weeks. Generic guanfacine was one of the products waiting for the resolution of the warning letter and we did not include it in the 14 potential generic product launches for 2015,” stated Fred Wilkinson, president and chief executive officer of Impax. “We are now evaluating the viability of this very competitive, multiplayer market and potential commercialization of this product. Additionally, we will continue to work with the FDA toward approval of our pending Abbreviated New Drug Applications at our Hayward facility.”

Branded and generic sales of guanfacine ER tablets (1 mg, 2 mg, 3 mg and 4 mg) totaled U.S. sales of about $689 million for the 12 months ended in August, according to IMS Health data reported by Impax.