But increases diarrhea on a scale thought unfathomable? Every time you meet one of those 'life extension' types taking Metformin just know that they aren't living their best life in the bathroom.
The GI side effects of metformin are usually short lived. They tend to last about a week or so after starting the drug or increasing the dose. Some people do have longer lasting side effects, but metformin is one of the best tolerated drugs we have.
I took metformin for about two weeks after being incorrectly diagnosed with T2 diabetes (I actually have T1, but some doctors seem to think it's impossible for adults to be diagnosed with it) and stomach / digestion / diarrhea issues only lasted about 2 days for me.