The present invention relates to metformin for use in treating a patient, wherein the patient exhibits an increased level of GDF15 in response to metformin treatment; to methods of identifying a patient who will benefit or who will not benefit from metformin treatment; methods of treating a patient at risk of developing or suffering from a disease or disorder comprising administering therapeutically effective amount of metformin; methods of adapting the dosage of metformin; the usage of GDF15 as biomarker for identifying a patient who will benefit or who will not benefit from metformin treatment, kits for use in identifying a patient who will benefit from metformin treatment and the use of the kits, as well as methods of treating a patient or who will not benefit from metformin treatment.