Hello, Let me start with metformin. Metformin is the mainstay of type 2 diabetes mellitus as we speak and it s the first drug that current guidelines suggest - although any choice would do provided that its effect on blood glucose would be adequate. Metformin does cause gastrointestinal issues including nausea and diarrhea. Starting with a low dose and taking it with meals usually reduces the discomfort and most patients get used to it after the next couple of weeks. If the symptoms are too serious to bear with then alternatives have to be tried. There are many alternatives including the DPP4-inhibitors (like sitagliptin), glitazones (like pioglitazone), sulfonylureas (like gliclazide), insulin (basal insulin to start with), GLP-1 agonists (like exenatide) and gliflozins (like dapagliflozin). Other less popular choices may include drugs like acarbose and nateglinide. Your doctor should decide what s best for you depending on your medical history and tests and whether you may have any contraindications for certain drugs or not. Hope I have answered your query. Let me know if I can assist you further.