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..