Metformin intolerance after many years of use?

I’ve been having a “loose bowel” problem for two months now. It started as diarrhea with a bad cold or flu that took forever to go away (about a month). I haven’t been to the doctor about it yet, because it gets better, then all of a sudden I have a bad day or two. I am concerned about IBS, possibly, but I’m not ready to go there yet.

I noticed that a few times in the last month when life has conspired to miss a day of metformin, it seemed to get better. Since I’m pumping with a CGM, I can safely miss or stop the metformin without a BG consequence – I just use a bit more insulin in the form of corrections.

So, I’m taking a metformin vacation to see what happens with my colon. I was curious, though, if anyone has experienced, or heard of tolerance for metformin deteriorating, and the typical side-effects showing up and becoming a problem. I’ve tolerated it well for years, but maybe I’m getting more sensitive now?

Metformin is supposed to work in three ways, it increases insulin sensitivity, it decrease glucose production by the liver and it reduces the absorption of glucose from digested carbs. It is my theory that a key element of the classic “gastric distress” and the reason it is sometimes called “metfartin” is that when carbs are not absorbed by the small intestine then they are fermented in the large intestine. And it is this fermentation which causes a problem.

There is a large crowd that argues that this fermentation is a primary cause of IBS. One way of figuring it out is to track what you eat and see if there is a correlation between what you eat as fermentable foods and the IBS. There is even a class of foods (FODMAP fermentable oligo-, di- and mono-saccharides and oplyols) which are thought to be the types of things which might be IBS triggers. In either case, stopping metformin may reduce/eliminate the IBS but it may not actually be that metformin is the cause it only adds on top additional fermentable fuel.


Yep I had explosive diarrhea for 15 hours before I had to give it up. You can try the ER version, seems to help, but I had vomiting everyday from that. Stopping it, both problems cleared up.

I couldn’t tolerate metformin from the start, so I don’t have “personal” experience; however, though I don’t know about that kind of intolerance, but my mother was on metformin for 17 years, after which her doctors decided that it had started making her anemic. Life is a constantly changing process, so, as my endo says: The fact that a symptom or respose hasn’t been seen before in any other patient is no proof that is isn’t happening to you.

I developed a problem which I thought was due to Metformin after many years of taking it, where I was feeling intense pain after taking my metformin each morning. It was a bit better when I stopped, so I assumed it was drug related. Come to find out, when I finally got to a Gastroenterologist and got scoped, that I had an unusual yeast infection which was not visible on the scope but turned up in the biopsy of the tissue. After I took some heavy duty meds for that infection and waited another couple months for things to heal, the “metformin-related” pain went away completely.

So you might have picked up some kind of intestinal bug or have developed diverticulitis, or something else that the metformin makes you feel more but which isn’t caused by it.

I’ve been taking metformin since my diagnosis in 2005 (T2). I’ve also had gastric issues with it, but it comes and goes. Never thought of tracking it to see if I could find any correlations to what I’m eating. Thanks, Brian, for the info. about what causes the symptoms.

1 Like

Well, the metformin is definitely a part of it – I’ve stopped, started, and stopped again over the last week, and the bowel issues tracked 100%. I’m now back to regular bowels (and so happy about it).

Jenny, I’m scheduled for a colonoscopy anyway… I’ll mention this to the gastro, so he’s aware of it. My endo is already in the loop.

Fortunately, I treat with insulin, so the main effect this has had on me is just increased insulin dosing. Still keeping excellent control, although my swings are a bit more dramatic.


Even though I am very insulin sensitive, I found that metformin dropped the amount of insulin I needed quite significantly. From 3 units to 2 to cover a meal, for example. I have read that it does this for people with Type 1, too. I assume this is because of the way it stops the liver from dumping glucose, but who knows?

Good luck with the gastroenterologist. Because I ended up with that occult yeast infection in my esophagus, despite very good control, I have to wonder how many others of us with diabetes are contending with something similar which doctors ignore because they assume that any digestive issue is due to the metformin.

I was wondering if this was a candida problem and were you treated with fluconazole? You only said heavy duty meds which left me wondering if the yeast problem was treated with an anti-fungal medication. How long did it take for the intense pain to go away? in my experience I have found most doctors don’t seem to consider the possibility of yeast being the culprit. I have been doing well with Metformin for 7 years, but my doctor thought I had suddenly developed an intolerance for it.

Hey, has anyone had their kidneys suddenly start failing after taking about 6 pills per day?

I am not aware that Metformin itself causes kidney failure. If you have had diabetes for years and have not had great blood sugars that can start to cause kidney failure. Once you have kidney issues your doctor should monitor your condition closely as you may not properly excrete Metformin. In bad cases this may cause a buildup of metformin in your body and a put you at risk for a condition called lactic acidosis

Let me ask. Why do you think you have kidney failure? Did you get some test results that were off? Did you see a kidney specialist (nephrologist)? Having a single test such as microalbumin be “off” doesn’t really mean your kidneys have failed.

I can only speak for myself, but I’ve never really “tolerated” Metformin well. I take it because it does an outstanding job of dampening my Dawn Phenomenon spike (and exercise spikes, to a lesser degree). In fact, I’m recently on a “getting worse side effects” part of the cycle, it seems. Terrible, persistent diarrhea is really the only side effect I experience, along with gassiness. I have a doctors appointment this morning that will cover that as well as other things.

So far, it’s seemed worthwhile. But, I’m experiencing some other issues… my fasting BG is steadily creeping up over the last six months even though everything else is stable (diet, exercise, dosage, etc.). I’m now over 100 mg/dL as often as I’m under, and never under 95 mg/DL (for reference, six months ago I was in the 75-85 mg/dL range 90% of the time). I’m also losing weight (this is from having low-insulin production, I think, not from Metformin). So, I’m planning on exploring other medication ideas with my team (which will soon have an endocrinologist…it’s hard to get an appointment with one in my neck of the PNW).

So yeah, for me, the Metformin side effects have been persistent but worth it. Not sure how I’ll feel about that in another six months.

Hi Brian,

Okay, not really kidney failure but they dropped to working at 78%. But within 7 days of stopping all meds (except Lantus) they are at 100%. I’ve got another soon. I’m still off most meds…feels good for me but, not my body. My high BP meds mixed with metformin is not a good mix on my system. Frustrating.

You didn’t say what test. eGFR is “estimated” GFR and is very susceptible to distortions. If you are dehydrated that can really mess it up. Usually a single eGFR test that is problematic has to followed up by a second test before a doctor will even decide that there is more to look into. I would recommend working with your doctor to better understand whether youd have any kidney issues before getting upset.

1 Like