Metformin is commonly used in the treatment of type 2 diabetes and polycystic ovary syndrome. Beyond these common applications, it also holds promise in treating chronic pain, and as an antiaging and anticancer agent. In addition, it has cardiovascular protective and neuroprotective effects. However, elevated concentrations of metformin in the plasma, such as in patients with renal impairment or with conditions that can disrupt lactate clearance, could cause metformin-associated lactic acidosis. Moreover, metformin can cause a deficiency of vitamin-B12 and folic acid and impact one-carbon metabolism negatively. This study employs micro-extraction procedures to extract metformin from the human plasma and blood glucose test strips followed by detection using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Under the optimized micro-extraction procedures and by using an eco-friendly base and solvent, the proposed method required only 10 µL of the human plasma and a small piece of the blood glucose test strip for metformin analysis. The method exhibits a linear range of 0.05–5 μg mL−1 with a coefficient of determination (r2) of 0.999 and a limit of detection of 0.01 μg mL−1. The relative standard deviation (RSD) and relative error (RE) were both below 6.7 %. The test strip is a disposable product; its reuse before disposal could increase its additional applicability. Furthermore, major blood proteins and their modifications could be identified using this tiny volume of blood by mass spectrometry after protein digestion. The proposed technique could be invaluable in point-of-care diagnostics, enabling rapid monitoring of metformin plasma concentration and major plasma proteins to help patients mitigate the risk of metformin-associated lactic acidosis. To reduce organic waste in clinical applications, micro-extraction is a simple and efficient protocol for sample preparation using minute volumes of blood samples.