The present invention relates to metformin glycinate salt and pharmaceutical compositions thereof for the treatment of diabetes mellitus. The method includes administration of the metformin glycinate salt by various routes selected from oral, intravenous injectable, intramuscular injectable, nasal, intraperitoneal, or sublingual, in order to achieve a reduction in blood glucose levels. The invention further relates to the synthesis of a new 1,1-dimethylbiguanide glycinate salt, called Metformin Glycinate. The resulting salt exhibits advantages over other metformin salts. These advantages are due, in the first place, to the fact that the glycine counterion exhibits hypoglycemic effects by itself. Moreover, the salt exhibits more rapid absorption, reaching higher plasma concentrations than those produced with metformin hydrochloride.