I have heard that Metformin can damage the kidneys. Is it true? One of my relative was given this tablet at a government hospital. But he hesitates to use it, because he thinks that he has to use it life-long. Can you explain this?
Metformin is the most commonly used medication for type 2 diabetes in the world. It is derived from a plant called ?Goat?s rue?. Its main effect is to reduce insulin resistance in the body, by which it improves blood glucose level. 
Metformin has no side-effect on the kidneys. But it cannot be given to people with already existing kidney disease, if their serum Creatinine level is ?1.5mg/dL (males), ?1.4mg/dL (females). This is due to the risk of a side-effect called ?lactic acidosis?. Metformin is cleared by the kidneys once it is used by the body. If the kidneys are already damaged, then metformin can accumulate in the body and lead to the said side-effect.  People with diabetes can develop kidney damage if their blood glucose is uncontrolled for a period of time. Therefore, metformin can protect the kidneys by lowering glucose level rather than damaging it.
It is true that some people may need to take metformin life-long. Type 2 diabetes can be reversed in many people if they adhere to strict lifestyle changes.  This is true for people newly diagnosed with type 2 diabetes or people who have had the disease for a shorter period. In such situations, the diabetes medicines, including metformin can be discontinued under careful supervision of a physician experienced in treated diabetes. Self-discontinuation of treatment without the advice of a qualified physician can pose great danger to one?s health.
The details about different actions of metformin can be found in the answer to question 02.
To know about different types of diabetes refer the answer to question 04.
- Bailey CJ. 2017. “Metformin: historical overview.” Diabetologia 60(9):1566-1576. doi:10.1007/s00125-017-4318-z.
- Silvio E. Inzucchi, Kasia J. Lipska, Helen Mayo, Clifford J. Bailey, and Darren K. McGuire. 2014. “Metformin in Patients With Type 2 Diabetes and Kidney Disease; A Systematic Review.” JAMA 312(24): 2668?2675. doi:10.1001/jama.2014.15298.
- Taylor, R. 2008. “Pathogenesis of type 2 diabetes: tracing the reverse route from cure to cause.” Diabetologia 51: 1781. doi:10.1007/s00125-008-1116-7.