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Biguanide (Metformin)

The primary action of metformin (a biguanide) is to improve insulin sensitivity. This reduces blood glucose by reducing glucose release from the liver and increasing glucose uptake in tissues (muscle and fat).

1. Therapeutic Considerations with Metformin

All information from medication product monograph unless referenced below.

A1c Lowering 1 - 1.5%1
Hypoglycemia Risk Low
Side Effects Nausea, diarrhea although often well-tolerated if titration is slow.
Vascular Protection Yes
Weight Neutral 
Cost, Blue Cross coverage;  strengths;  dosing frequency; indications

Visit Metformin in the Complete Diabetes Medications Table  

Combination Medications Visit combination meds on Complete Diabetes Medications Table
Advice for times of dehydration, vomiting, diarrhea To avoid concerns with reduced medication clearance, Diabetes Canada advises metformin be stopped until these symptoms are resolved. Adequate hydration should be promoted. 
  • Metformin is a well-established agent with a long-term safety profile.
  • Reduce dose if eGFR <60 mL/min/1.73m2. 
  • Contraindicated in advanced hepatic or renal dysfunction (eGFR < 30ml/min/1.73m2). Some specialists may continue to use in this setting depending upon the client’s status.
  • May cause a vitamin B12 deficiency. Query if macrocytic anemia or peripheral neuropathy. 
  • May enhance fertility in women with polycystic ovary syndrome (PCOS).


2. Dosing Considerations with Metformin


1. Inzucchi SE, Bergenstal RM, Buse JB, det al. Management of hyperglycemia in type 2 diabetes: a patient-centred approach. Diabetes Care 2012; 35: 1364-79.  (Accessed Feb 26, 2018).