The new drug that is replacing metformin is GLP-1 agonists like Trulicity, Mounjaro and Ozempic.
Other drugs that can replace metformin are SGLT2 inhibitors like Forxiga and Jardiance as well as TZDs like Pioglitazone and DPP-4 inhibitors like (Januvia, Tradjenta), Sulfonylureas (Glipizide, Glyburide).
Mounjaro has strong glucose control and weight loss and SGLT2s help with heart and kidney health, although the best choice of drug to replace metformin depends on your individual factors like A1C, side effects, weight and any other health issues that always require your doctor's guidance.
Metformin was not actually banned in the US, although in 2020, the FDA requested a voluntary recall of specific lots of extended release ER metformin as a result of contamination with N-nitrosodimethylamine (NDMA) which is a probable carcinogen that was found in levels above the acceptable limits.
The immediate release form of metformin though was not affected and people taking metformin were told to keep taking their metformin until they got replacements, as the risks of stopping diabetes treatments outweigh the NDMA concerns.
The A1C level that metformin should be started is when your A1C level is 7% or higher.
And for people with prediabetes, specifically with A1C levels between 5.7% and 6.4%, metformin is not the standard first line treatment and should only be considered for people at the highest risk.
And in cases of severe hyperglycemia, (A1C>9-10%) with symptoms, insulin is usually the recommended treatment instead.
An A1C level of 7% is the typical starting point for beginning metformin therapy for type 2 diabetes.