Forest Pharmaceuticals has agreed to pay more than $300m to settle charges that it improperly marketed two products.

The firm pleaded guilty to obstructing a US Food and Drug Administration (FDA) investigation and other misdemeanour charges.

The charges primarily relate to Forest’s marketing of Levothroid (levothyroxine sodium tablets, USP), an unapproved drug used for the treatment of hypothyroidism.

A 1997 Federal Register notice announced that these products are considered “new drugs” within the meaning of the Federal Food Drug and Cosmetic Act (FDCA) and forced manufacturers to obtain approved applications from the FDA by August 2000.

Because levothyroxine was considered a medically necessary product, the FDA permitted a gradual phase-out to cease no later than August 2003, but Forest increased its distribution and ignored a subsequent letter warning them to stop halt the drug’s manufacture and distribution.

Forest Pharmaceuticals is also charged with the off-label promotion of its Celexa antidepressant for paediatric use, when it had only been approved for the treatment of depression in adults.