Metformin will have some effect if taken without a meal but, to have maximum effect, it should be taken with meals. There is a small risk of hypoglycaemia if taken without eating. This article discusses the situation where people do not eat the classic 3 meals a day. https://www.pharmaceutical-journal....ls-and-doses/11123225.article?firstPass=false It says:- "As a result, metformin is now commonly prescribed in a twice daily dose, taken with the two largest meals of the day and not necessarily with breakfast and the evening meal. This dosing allows higher doses (eg, 1g bd) and more convenience for the patient."