Most people who are diagnosed with type 2 diabetes are given a prescription for metformin – and for a good reason. It’s a cheap, effective generic pill whose safety has been proven for more than 50 years. But like any prescription drug, there are possible side effects, drug interactions, and other issues that you should know about.

What metformin does

With type 2 diabetes, the body doesn’t make enough insulin or isn’t able to use it properly to control glucose (blood sugar) levels. Metformin reduces the amount of glucose your liver produces, and also improves your body’s ability to use the insulin it makes. Metformin doesn’t cure diabetes, but it provides better blood sugar control.

And that’s not all. By lowering your triglyceride and LDL cholesterol levels, metformin helps reduce the increased risk of heart disease or stroke that comes with type 2 diabetes. Also, by controlling blood sugar levels it helps to reduce your chances of diabetic complications in the eyes, kidneys, feet and elsewhere. Of course, even with a drug as powerful as metformin you still need to eat and exercise properly to successfully manage diabetes.

What are some common side effects of metformin?

Many patients find that metformin takes some getting used to. It may cause diarrhea, vomiting or an upset stomach at first, especially if taken on an empty stomach. You may also notice gas or a metallic taste in your mouth. Not everyone has such problems, but they are the reason why your doctor may start you out on a small dose and carefully increase it over time. The good news: these unpleasant symptoms usually go away within a few weeks.

Rare side effects to watch for include pain in your muscles, headaches, heartburn, constipation, and flushed skin. Tell your doctor about these or any other symptoms you notice, whether they appear when you first start taking metformin or after you have been taking it for a long time.

Chest pain or a rash may be signs of a serious problem and you should seek medical help immediately.

Finally, in a very small number of cases metformin may cause a dangerous buildup of lactic acid in the blood, called lactic acidosis. Symptoms include feeling unusually weary, being drowsy or dizzy, or having chills, muscle pain, breathing problems, heartbeat that is slow or irregular, upset stomach, vomiting, or diarrhea. Tell your doctor about such signs right away.

Is metformin safe to take with other drugs?

In most cases, yes. But just about any medicine will interact with some other medicines, and metformin is no exception. Drug interactions may lead to side effects, or may change how well your medicines work. Metformin may interact with quite a few other medicines, including some common blood pressure pills, birth-control pills and even some over-the-counter decongestants.

To be safe, tell your doctor and your pharmacist about everything you take: prescription and over-the-counter medicines, vitamins and herbs. They are the experts who can help you prevent or minimize drug interactions by adjusting your medications or doses as needed.

What about foods?

You don’t have to avoid any particular foods with metformin. But drinking too much alcohol increases your chance of developing lactic acidosis.

Where else might I find metformin?

Metformin is also sold as a name-brand drug under several names including Glucophage, Fortamet and Glumetza. Also, it is an ingredient in several combination pills including Janumet, Avandamet and Kombiglyze XR.

Knowing the facts about metformin shouldn’t discourage you from taking it if your doctor recommends it. Metformin has helped millions to safely achieve better diabetes control.

To learn more about diabetes medicines:
Can Diabetes Pills Help Me?
Diabetes Medications: Managing Side Effects
When to Update or Change Your Diabetes Medications