As @pauleckler may well recall from the H&N board, my suggestion to anyone who was being advised on their medication by an internet pundit…regardless of qualification…was to listen to their chosen provider for one simple reason. Being in the same room, knowing the patient’s history, actual diagnosis, goals, risk tolerance etc.etc has an incredible effect on appropriate joint decision making.
I’m not suggesting your BIL’s advice a decade ago was wrong for your circumstances back then…probably correct in that he was emphasising the greater potential for harm (both from the disease itself or the medication) if you allowed things to progress. I’d do that under similar circumstances…in fact, I’d have probably pointed out even earlier that medications with side effects were in your future if you didn’t make some lifestyle adjustments. After all, a need for something even as innocuous as metformin doesn’t come out of left field unannounced for most folk.
So called minor side effects aren’t always minor to the person who’s experiencing them