Metformin Cheat Sheet

If you have diabetes or know someone that does, you’ve probably heard of Metformin. There’s a lot of information on this medication so it can take a lot of work to research basic questions. We compiled this “cheat sheet” to save you time by answering some of the most common questions on Metformin.

What is Metformin?

Metformin Hydrochloride (aka Metformin) is used to improve blood sugar (glucose) in people with Type 2 diabetes.  It’s a very common medication and is a first line treatment for people with diabetes. 

Metformin is a generic drug that has been in circulation for decades, initially approved by FDA in the 1990s. It’s also available under the common brand names Glucophage, Frotamet, Glumetza, and Riomet.

Aside from diabetes, it’s also used to treat other conditions such as polycystic ovary syndrome, non-alcoholic fatty liver disease, and hyperinsulinar obesity.  

How does Metformin work?

Metformin lowers both baseline (basal) and after-meal (postprandial) blood sugar. It does this by decreasing the glucose produced by the liver and reducing glucose absorbed in the intestines.  It also improves insulin sensitivity by increasing glucose uptake and usage within the limbs. 

To put simply, Metformin doesn’t change insulin secretion but makes your body use and store glucose more effectively.

How to take Metformin?

Metformin is often taken as a pill and available as extended release or immediate release.

When used to treat Type 2 diabetes, Metformin dosage for immediate release typically starts at 500 mg twice daily or 850 mg once a day and is taken with meals. For extended release dosage starts at 500 mg to 1000 mg once daily and is taken before sleep. 

If your blood sugar isn’t improving with the starting dosage, your care provider may increase dosage. Dosage is usually adjusted up in increments of 500 mg per week with a max dosage usually set 2,000 mg per day.

taking metformin

How long does it take for Metformin to work?

Most people will start to see the effects (i.e. lower blood sugar) within 2-3 days and can last up to 2 weeks. Immediate release Metformin is most effective 2-3 hours after ingestion and extended release is most effective at 4-8 hours.

But keep in mind these timeframes can vary based on dosage and individual factors.

What are the side effects?

Like any medication, Metformin does have side effects.  The more common reactions include diarrhea, gas, nausea or headaches and generally occur at the start of treatment.  These conditions are usually minor but consult your care provider if they last for several days.  

A more severe side effect is lactic acidosis, which is a build up of lactic acid in your bloodBut according to this review of Metformin-associated lactic acidosis, the incidence of lactic acidosis is very low and is associated when there is kidney complications or disease. 

Liver inflammation or damage is also a potential side effect but appear to be very rare based on these studies on Metformin-induced hepatitis and hepatotoxicity.

Can I take other medications?

Generally yes, but always tell your care provider about any medications or supplements you’re taking in case they can have a negative reaction with Metformin.

What if I have preexisting conditions?

Below are conditions where taking Metformin will need special attention and should be discussed with your care provider.

Bariatric surgery

Bariatric surgeries, like gastric bypass or sleeve gastrectomy, reduce the size of or completely bypass the stomach. These surgeries can change how Metformin is absorbed.

For instance, this study shows bariatric surgery resulting in more frequent emptying of the stomach, which could reduce absorption of extended release Metformin. Your care provider may opt to prescribe immediate release Metformin instead as studies show that its absorption may actually increase after gastric bypass.

Kidney and Liver conditions

Because Metformin is excreted by the kidney, dosage adjustments may be needed for people with kidney disease or complications. 

If you have severe kidney dysfunction Metformin can lead to more serious side effects and shouldn’t be taken (this is called a Metformin contraindication). Also, people with liver conditions may have an increased risk of lactic acidosis (discussed above).  


Elderly people generally tolerate this medication well but dosage may be kept lower to account for slower clearing from kidneys.

Vitamin B12 Deficiency

Taking Metformin over time depletes Vitamin B12 levels. You can ask your care provider to check your vitamin B12 levels annually to monitor for any deficiencies.

Pregnancy & Breastfeeding

Metformin crosses the placenta and can also be found in breast milk. While studies have not shown an increased risk for the baby, discuss with your care provider if this medication is right for your situation.

pregnancy and metformin

Insulin may be a better alternative treatment if you’re pregnant or breastfeeding since it’s only used by your body and does not cross the placenta.


What happens if I miss a dose?

If you miss a dose or two, your blood glucose will probably increase but may not cause immediate harm.  Resume taking your dosage and monitor blood glucose to see if they lower. Do not take extra doses to make up for missed doses. 

Can I take Metformin and alcohol?

Drinking alcohol excessively while taking most medications can increase risks of complications. This also applies to Metformin since combining with alcohol may increase the risk of lactic acidosis. General guidance is to consume minimal alcohol while taking this medication.

Is it dangerous?

Given its long history and relatively mild side effects, Metformin is generally safe and tolerated well by most people.  But it’s important to communicate any preexisting conditions or other medications/supplements you’re taking when discussing with you care provider.

How long do I need to take it?

This depends on when you reach the target blood sugar levels your care provider assigns.  The American Diabetes Association (ADA) has guidelines for glycemic targets which many care providers use. The ADA recommends targets of having Hemoglobin A1C less than 7% and/or a pre-meal glucose between 80-130 mg/dl.

Are there food restrictions with Metformin?

Metformin is generally well tolerated with food. But there are some foods you may want to limit or avoid while taking Metformin because they can make side effects worse.


Medication is an important part of daily life for many people with diabetes and their diabetes self care. And it’s the first line treatment for diabetes and has been used for many years.

We answered the most common questions, whether you’re considering this treatment for yourself or to help someone you know. Always discuss medications with your care provider but it’s important to be informed so you’re confident about your diabetes treatment and self care.

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