Which medication is known as Metformin ER?

Metformin ER is best known by the brand name Fortamet. This formulation of metformin is designed to provide extended-release action, allowing for once-daily dosing that can help improve adherence to the medication regimen and reduce gastrointestinal side effects commonly associated with metformin. Extended-release formulations release the active ingredient more gradually into the bloodstream compared to immediate-release versions, which can lead to a more stable blood sugar control over the day.

While Glucophage is another brand name for metformin, it represents the immediate-release formulation and not the extended-release form. Riomet is a liquid formulation of metformin and is not classified as an extended-release product. Insulin, being a different class of medication used primarily for diabetes management, does not relate to metformin's structure or function.

Thus, Fortamet is indeed the correct answer, directly tying its identity to the specific extended-release version of metformin.