What is the most common side effect associated with the diabetic drug metformin?

The most common side effect associated with metformin is diarrhea, which occurs in a significant number of patients taking this medication. Metformin, primarily used to manage type 2 diabetes, can cause gastrointestinal disturbances as it influences how the body processes carbohydrates and glucose. The mode of action of metformin involves decreasing liver glucose production and increasing insulin sensitivity, which can lead to effects on the gastrointestinal system.

Diarrhea is particularly common when patients first start the medication or when they increase their dose. This side effect typically occurs due to metformin's ability to increase intestinal motility and affect the gut microbiota. While many people may experience this side effect, it can often be managed by taking the medication with meals or starting with a lower dose and gradually increasing it.

In contrast, low blood sugar, while a concern for diabetic medications, is not a common side effect of metformin because it works primarily to improve insulin sensitivity rather than directly increasing insulin levels. Sleepiness is not typically associated with metformin. Changes in pH are more relevant in contexts related to metabolism and certain other medications rather than being a common side effect of metformin.