A 52-year-old man with obesity and hypertension is newly diagnosed with type 2 diabetes mellitus after fasting plasma glucose of 8.5 mmol/L on two occasions and HbA1c of 57 mmol/mol (7.4%). He has no symptoms of hyperglycaemia and no established cardiovascular disease or kidney disease. Lifestyle measures have been discussed. According to Australian primary care diabetes guidelines, what is the most appropriate initial pharmacological therapy?