February 21, 2011

Differing Brands of Generic Metformin Behave Differently

Dr. Bernstein has been preaching about this on his web telecasts for years, but it bears repeating: If you are having problems with generic metformin or not seeing it make much impact on your blood sugar, change brands before you assume it isn't working or that you can't tolerate it.

I just had this message brought home to me when my pharmacy (Walgreens) filled my prescription for metformin ER with tablets from SunPharma instead of the ones from Teva they'd given me for years.

The pills were about half the size of the ones I'd been getting, which suggested they contained less of a matrix substance to slow the release of the metformin. And sure enough, when I took the same dose I had been taking with no problems with the Teva brand metformin, I felt exhausted and semi-poisoned. It felt just like when I had taken an overdose of metformin some years ago, when my family doctor prescribed an overdose after confusing the dosage instructions for regular metformin--which can be taken in larger doses--with those of metformin ER.

Not only that, but my fasting blood sugars went up. Clearly the SunPharma metformin ER was not behaving like a true extended release should and releasing slowly through a 24 hour period but was hitting my blood stream all at once and then was done.

A quick visit to Google revealed that Sun Pharmaceuticals is an Indian company and that in the past the FDA has forced them to recall batches for quality issues.

When it was time to refill my prescription, I called my pharmacy and spoke with the pharmacist who shrugged off my concerns and told me I'd have to speak to the pharmacy manager (not available that day.) So I got on the phone and called other local pharmacies and asked them what brand they were dispensing. Two of them still carry the Teva brand, so I took my empty pill bottle to the closest one and they transferred the prescription and filled it with the Teva. I was very happy to find that it worked just the way I remembered, with no unpleasant side effects.

This experience made me wonder how many of the people who tell me they can't take metformin because of the side effects were victims of cheap versions like the SunPharma one.

If you try metformin and find the side effects overwhelming after a month's trial--typical problems would be dramatic digestive problems or a feeling of exhaustion and low grade toxicity--talk to your pharmacist about trying another brand or move your prescription to another pharmacy that carries another brand.

Dr. Bernstein says that the brand name version, Glucophage, is the best. I've never tried it so I can't verify that. If you can get it, go for it. I've heard that some pharmacies will order a specific brand for you if you ask, but before you do this, check how much the prescription will cost you as some insurers may not pay for your prescription if you specify the brand or they may make you to pay much more.

If you're taking metformin ER, which brand you are taking? How well does it work for you? Have you switched brands and seen a difference? Please cite the manufacturer name if you can. It would be nice to build up some expertise here as to how the different versions work. If I get enough feedback I'll add it to the page where I describe metformin on the Blood Sugar 101 site.

NOTE: You should be able to find the name of the manufacturer somewhere on your label. I believe this is a legal requirement in the U.S..



Rairy said...

Not sure what brand it currently being used by my pharmacy but the exhaustion you talk about is all too familiar.

My pharmacy has a bad habit of "generic shopping" and I find the size/shape/color of most of my generics changing with each three month refill as they change from one manufacturer to another to another.

Bruce Parr said...

I have had a ton of bizarre experiences. I had the exhaustion, breathing problems, and digestive problems with the non-ER Metformin. My doc switched me over to ER twice a day. Much better, but I will still occasionally get the same issues. I have also had what I call placebo batches. No change in diet, no illness, no change in exercise, and multi-day increases in BG of 70-100 points. Then I get a pill that works and my numbers plummet because I cut back. the quality control is all over the map.

Fitnatic said...


I have really BAD experience with TEVA. Teva pills are the worst! Lots of gas, tiredness and diarrhea!

I used to get other generic pills before and none gave me as bad a reaction as Teva. After I read your recommendation about taking teva couple of hours after meal - I decided to try it and still no difference. Maybe I should try those Sun pharmaceutical ones since they did not work for you and we seem to have opposite reactions to brands. :)

Jenny said...


The SunPharma made me feel much worse, giving the the impression that it was concentrating the dose all at once, so I'm not sure that would be what you were looking for.

njoy said...

Jenny, I am new here and in deep doo doo with my type 2 diabetes.

I was diagnosed 12 years ago with fasting bg level of over 300. I felt fine so it was a surprise to me. I started metformin and tried to do the diet/exercise thing. I lost a lot of weight and thought I was doing well but my bg was not great and my doctor insisted that I quickly lose another 10 lbs and start walking a full hour every day.

This had the effect of flipping me into an eating binge (I was STARVING) and I also got plantar fasciitis in both feet. I quickly gained back most of the weight I'd slowly lost

By then, I was feeling sick and when my doc upped my metformin I suddenly felt like I was dying. He wouldn't take me off metformin so, after much thought, I quit the meds and started on insulin. At the same time, I moved and got a new doc.

A few years later, my bg started to fluctuate wildly. I could NOT control my appetite. A diabetic educator said I would be better off with high blood glucose levels than fluctuations.

Also, I started breaking out in huge hives whenever I injected insulin. Again, my doc was not very interested and said it was "probably" not a real allergy, just a sensitivity. I've been referred to a local internal medicine specialist who will refer me to an allergist or endo "if needed".

Long ago, I ditched the low fat, high carb diet recommended by the nutritionist and started lowering my carb intake. After I stopped taking insulin, I went on Dr. Mercola's Advanced diet which is very strict low carb.

The improvement in the way I feel is amazing. My appetite is under complete control and, until I hurt my back, I was exercising one hour a day. Now, my back is better so I've bought a rebounder and started slowly experimenting with that.

Anyway, I do what I can and I feel really good BUT my bg about 200. Nothing makes any difference, including exercise.

I really do not know what else to do. I live in rural Canada and will have to wait 3 or 4 months to see an endo (if I'm referred). That's because specialists trained here can make twice the money in the US.

Meanwhile, my latest doc has decided I am non-compliant (well, I suppose I am but didn't feel I had a choice). She has become very cold and distant with me and refuses to look at me or discuss my situation. There are no other doctors taking new patients in my town so I am stuck.

She wants me to go back to the diabetic team but this has not worked in the past. They are less inclined to stuff me with carbs these days (thank goodness) but the diet still doesn't work for me and I am afraid I will put all those pounds back on AGAIN.

If you have any thoughts, I would greatly appreciate hearing them. The Canadian medical system is not exactly broken because, in my experience, most people do get good care and, of course, it is cheap or free. That stops, however, as soon as you get are labeled non-compliant.

My thinking is that I have stopped producing insulin and since I can't take it (I'm petrified to inject, to tell the truth) I don't know what to do. I am afraid I will end up in hospital feeling horrifyingly sick from meds I can no longer refuse.

Thanks for listening, Jenny. I will continue reading the web site. I have already stopped taking excess amounts of Vitamin D, thanks to you.

Jenny said...


If you were injecting NPH insulin it is very possible you were allergic to the protamine added to slow the insulin. You could try one of the new analog insulins like Levemir and very likely be fine on it.

That would be the first thing to try. Alternatively if you were using one of the analogs, you might try Regular Human insulin at meals (Dr. Bernstein's book can explain how to dose it.) It works very well with a low carb intake.

Insulin allergy is a real though rare phenomenon and the usual treatment for people who are insulin dependent who develop the allergy is U-500 Regular human insulin which is highly concentrated--one unit is the same as 5 units of the common stuff.

I would save that as a last resort, though, until you've tried Levemir, Lantus (both long acting) and/or fast acting R, Novolog, or Apidra at meals. They are all different formulations and molecules and there's probably one that you wont' be sensitive to.

The back and tendon problems are blood sugar-related combined with certain genetic backgrounds. I've experienced the exact same problems in response to exercising (they run in my family down the side with the diabetes). I've learned the very hard way you have to be very respectful and pushing through the pain guarantees a year-long recovery til you can be active again.

Don't give up. I have heard from people with similar stories who eventually got to good doctors. You have to stand up to your doctor and demand what you need which probably is insulin and to try different ones until you find the one you can tolerate.

Unknown said...

I switched to Glucophage from the generic met and I've seen a remarkable difference in my bgs. Yes, I listen to Dr. Bernstein's teleconferences/webcasts and he's mentioned many times that the brand name Glucophage works much better than the generic. I've sure found that to be true! It is expensive but for me it's worth it.

njoy said...

Jenny, thanks for the good advice. It was Novolin ge NPH that gave me intense itching and eventually hives so I started to use NovoRapid. It was okay for awhile but then the itching started and eventually I broke out in hives from that, too.

I've just had an Hgb A1c test and know my bg is high enough that the doctor will probably cooperate with trying new insulins. Hope so anyway.

As far as the diet the diabetic team will want me on, I'm just going to cheerily continue with my own diet and refuse to up my carbs to suit them. They don't like my attitude, anyway, so nothing lost there.

Anyway, thanks for the response and I'm looking forward to exploring your blog.

njoy said...

Update: I had a great talk with a diabetic educator and she switched me to Lantus (24 units daily) with a bit of NovoRapid to follow any intake of carbohydrate (I am maintaining the low carb diet so don't usually take the R at all). This is an amazing improvement on my previous huge intake of insulin (anywhere from 60 to 200 units a day) and resulting overwhelming food cravings.

Amazing what some different advice can do.

Jenny said...


Glad to hear you are doing so well on the new regimen!

Nelle said...

I just took my first Metformin ER pill with dinner. I also wanted to use Glucophage per Dr. Bernstein- but my Dr said my insurance might not pay for it. I was diagnosed with Type 2 three years ago and have been managing with diet. My A1C was steady at 5.7 but recently went up to 6.1. I was also diagnosed recently with lobular carcinoma in situ (despite the name- not actually cancer but puts me at a very high risk). My Dr. decided it was wise to try the Metformin since it would not only help with my BG but studies have shown may help decrease breast cancer risk. I was happy to see that the manufacturer was TEVA. Wish me luck. I am SO hoping I won't have bad side effects. Since I eat no grains or starches, I'm hoping that I won't have bad gastric upset.

Jenny said...

Nelle, Whatever your experience with the first few pills, give it a few weeks before drawing conclusions. Most people do adapt.

gindie said...

For the last 10 days I have had this awful, persistent bitter taste in my mouth and on my lips. Two things happened 10 days ago, 1) I got a tooth filled with a composite (non-mettalic) filling and 2) I started taking TEVA Metformin (non-ER), after my pharmacy switched from Aurobindo.

The dentist said the filling wasn't the culprit. I'm wondering if the Metformin might be. I'm nearing 48 hours since my last dose and still have the strange taste.

Jenny said...


Sometimes metformin can cause a metallic taste. If the problem is the metformin it should go away within a week. If it is, ask your pharmacy to order the other brand. Some will, some won't. Rite Aid is good about ordering specific generic brands.

JeffD said...

In the past year I have taken the following manufacturer’s Metformin with varying results;

Sun – worked controlled BS well without noticeable side effects.

TEVA – worked controlled BS, daily gas and loose stools.

Amneal – Failed to control BS, digestive system unable to dissolve.

Mylan - worked controlled BS well without noticeable side effects

Allan said...

JeffD - thanks for the list of generics. I have been using TEVA Met 500mg ER for the past 4 ys with little side effects. It appears to be working - take at bedtime per physician and Dr. Bernstein to control dawn phenomena . Local pharm not using TEVA anymore; switching to Sun Pharm. I am afraid to change since not sure if it is going to affect me. I see that Sun Pharm on your list was effective. This encourages me to try it for a week.


scotty said...

im taking 500 mg generic metroformin ER tab AMN an my sugar goes up when taking any ideas

Jenny said...

Scotty, That is a very low dose. It's usual to start with the low dose to get your digestive system used to metformin, but it doesn't usually start lowering blood sugar until people are taking 1500 mg a day or even more.

Dignified Apartment Living said...

ickhave had type 2 for over 20 years, controlled it well with 1 glipizide, then got a new doc who discovered my a1c went up to 7.1, so he said I should take 2 free metformin that a local grocery pharmacy dispensed free of charge....my reading went up immediately to 250/day, went to a pharmacy and the pharmacist pinched the skin on my hand, said you are very dehydrated, stop the metformin and see your doc, I told the doc, after research, that metformin is a black label drug and he should have warned me and checked it within a week, he just stared at me and agreed i switch back to 2 doses of glipizide.

Jenny said...

Glipizide is a black label drug too--and research bears out that it damages the heart and raises the risk of heart attack.

The black label on Metformin refers to the possibility of lactic acidosis, since a related drug caused it. But it turns out that lactic acidosis occurs as commonly in people not taking metformin as in people taking it.

However, if your kidneys are damaged metformin can cause problems. I hope you have had the microalbumin test that should be done periodically for people with diabetes to ensure that they are okay. If they aren't, take seriously the need to lower blood sugar with diet or insulin.

Anonymous said...

What about Metformin ER made by Apotex Corp? I have been taking this for the last three weeks graduating to 2000mg daily and I have not lost any weight like some other have. I was already eating sensibly before starting the meds. The only thing I notice is significant fatigue, bloating and some constipation at times. I am also on Vitamin D2/ 1.25mg weekly dosing. I was prescribed these medications by my endocronologist for insulin resistance. I don't get to check my levels because I am not diabetic at this point. How do I know if this is working?

Jenny said...

You should not wait until you are fully diabetic to start testing your blood sugar because the best way to prevent diabetes is to ensure you aren't eating a diet that pushes your blood sugar high enough to damage your insulin-producing beta cells. By the time you are diagnosed diabetic half of them may be dead because many "prediabetic" blood sugars are high enough to kill beta cells via glucose toxicity.

Get a meter and use the strategy you'll find HERE to see what is going on and how effective your metformin is.

Anonymous said...

Dear Jenny,
Thank you for responding and for the good advice. Nice to know you are here!

Unknown said...

I recently had a mail order 90 day refill of Sun Pharma generic metformin XR. Took it for about two weeks and had a bad reaction (skin rash , burning legs and face and semi-poisoned feeling. Prior to that I took Teva metformin with no problems. I talked to my Dr and switched to Glumetza. It's a brand name but the company has a card that limits copay to $10. Hope it works

penny said...

Im in Australia & found this post after getting a different brand of Metformin XR. I usually get the Alphapharm brands which work really well ( i have taken them for years with no side effects ).

My Pharmacist then gave me a cheaper brand made by Apotex. I Immediately noticed a foul chemical smell & had trouble swallowing them because of the taste & the fact that they were slightly larger than my normal brand.

Im not sure how well they work because they gave me stomach problems & I could not tolerate taking them more than once. ( however im sure they would not work aswell for me because i was having trouble absorbing them).

I read the information leaflets & noticed the ingredients are different. I also noticed the Apotex brand are described as'Modified Release' instead of 'Extended Release' tablets.

It's important that people are aware that different brands of Metformin XR are not always equivalent & can affect you differently.

Rilla said...

I'm in Canada, and started taking metformin last March. I slowly increased till I was taking 500 mg 3x/day and was having no GI issues. Then I got my prescription refilled and noticed the pills looked different. Then I started having SEVERE GI issues. I called my pharmacist and he insisted it wasn't the brand change, sometimes "that just happens". I backed down to 500 mg for a month, but the GI issues never cleared up, so I called my pharmacist again, and asked him to switch me back to my original brand. He was no longer carrying that one, but agreed to order it back in. I'm on day two of 500 mg 2x/day and no GI issues. PHEW!! I'm so glad to hear I'm not crazy and this has happened to others too...

beammeupscotty said...

I changed to a mail order brand which I was sent 500 mg of TEVA. It gave me lots of gas and had no affect in controlling by BG levels. I am changing back to my other brand today however I do not know what the brand is but it worked for me. Bottom line for my body is that different metformin brands have different results and they are significantly different.