Joined an unwelcome but not unexpected club this week

What research led you to believe "there's very little downside" to metformin?

There's a full page (IIRC about 16) of potential side effects, and I had every single one of them my first month taking it.

Don't eat or drink grapefruit products while on metformin.

I took metformin along with insulin for almost 5 years.
I couldn't wait to get off it.
I finally proved to my former doctor that it wasn't effective by not taking it for 5 months between A1c tests and coming out with the same number (actually .1 lower without the metformin).

Metformin is often the first medication prescribed for diabetes because it is cheap.
It is a highly refined chemical compound that can lead to internal organ issues.

My cost for metformin was $8 for 90 days.
My cost for insulin for 90 days is $260. Up from 130 because I now have 2 kinds vs 1 kind and the metformin.

...but I am happier and less likely to have medication related health issues.