Metformin’s main site of action is at the liver to reduce the excessive sugar release seen in type 2 diabetes. Metformin does not cause weight gain, and is usually the first choice of medication to treat type 2 diabetes. However, if you have kidney or liver problems, heart failure, or are very sick, metformin cannot be used.
The main side effects of metformin are diarrhea and stomach upset or cramping. It is important to take metformin with food to reduce stomach-related side effects. A very rare side effect (less than 1 person per 100,000 patients taking metformin) is lactic acidosis (a build-up of lactic acid in your blood). Lactic acidosis is very dangerous, and usually fatal. Generally, the people who develop this rare side effect are the ones who shouldn’t have been taking metformin in the first place (people with kidney problems or heart failure, or alcoholism).
Metformin is also called a euglycemic, which means it may restore the blood sugar to normal or non-diabetic levels. If you are treated with metformin alone, you should not experience low blood sugars. And if you are treated with metformin and other blood sugar normalizing (“euglycemic”) agents (such as thiazolidinediones, starch blockers, or incretins) you also should not have low blood sugars. However, hypoglycemia or low blood sugars may develop when you take metformin together with insulin releasing pills and insulin, because they raise insulin levels and increase the risk of developing lows.
In short, metformin decreases glucose production by the liver
The most common side effects are:
- Diarrhea and stomach cramping
- Low blood sugars, when used in combination with insulin releasing pills (secretagogues) and insulin
A rare side effect of metformin is lactic acid build up.
For more information about Metformin pill strength (formulations), initial and final doses, side effects, and different Metformin containing preparations on the market, see our Medications Table.
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