Does Metformin Cause Kidney Damage?

The short answer is – no. There are myths about metformin causing kidney damage, but these stories don’t consider important details. Let me explain.

How Kidneys Work: kidneys filter circulated blood to produce urine. On average, humans produce about one gallon of urine daily and this is the end-product of kidney circulation and filtering of approximately 450 gallons of blood daily. Urine travels from the kidneys to the bladder through tubes called ureters and is then expelled through the genital urinary canal.

Metformin and Kidneys: Problems arise when metformin and its byproducts can’t be filtered out of the blood properly. This might happen in several common scenarios. One scenario is when there is sudden reduced blood flow to the kidneys (e.g. due to profound dehydration, or sudden drops in blood pressure due to serious heart problems). In other instances, there may be disturbance of flow in the blood filtration units of the kidneys responsible for proper waste elimination; the causes of this disturbance are clogged and narrowed filtration units (glomeruli) due to a loss of elasticity, hardening, narrowing and shrinkage. The result is an abnormal increase in permeability of the kidney filters measurable by the presence of proteins and red blood cells in urine which normally do NOT belong in urine. Some experts may correctly label this as a form of accelerated aging of the kidneys. Other common scenarios occur when there are problems with urine drainage downstream from kidneys resulting in backing up of urine up to the kidneys and pressure elevations in the kidneys (e.g. prostate problems, kidney stones or other obstructive barriers downstream from the kidney).

Moreover, one also needs to keep in mind the long term co-presence of hypertension in many diabetes patients. Hypertension has a highly damaging effect on kidney blood vessels and capillaries that leads to irreversible thickening and hardening (loss of elasticity) of blood vessels and capillary walls. In some instances of episodic jumps in blood pressure (e.g. malignant hypertension), common patterns are even necrosis of kidney capillaries.

Hence mythical stories about direct damage of metformin to kidneys often miss key factors that are important to viewing the situation in a correct context. Such stories (often unintentionally) fail to consider an accurate sequence of events and/or changes in kidneys, as well as cause and effect. As a result, such myths lead to unfounded impressions of kidney damage “due to metformin intake” and fail to factor in other important preceding changes that are key. Conclusion: While metformin is safe for most people, those with significant kidney damage need careful monitoring to prevent rare complications like Lactic Acidosis. To prevent kidney damage from occurring, work closely with your health care provider to monitor and control blood pressure as well as blood glucose trends. If a person on metformin develops a fever, persistent vomiting or diarrhea (all of which can lead to severe dehydration), seek help from your health care team so that metformin can be temporarily paused to minimize risks of its overaccumulation.