Background Plant parts of Moringa oleifera Lam. (Moringaceae) is known to lower blood glucose level and as a result, type 2 diabetes mellitus patients (T2DM) sometimes use it as herbal supplements. This study therefore sought to evaluate the effects of coadministration of Moringa oleifera tea on steady state concentration of metformin in ambulatory T2DM patients attending a tertiary health facility in Nigeria.