Medications to Avoid While Taking Metformin

Metformin is usually the first-line drug of choice for patients with type 2 diabetes mellitus. 

If you’re taking metformin for diabetes, you probably want to know if it has any drug interactions.

What is metformin?

Metformin is a popular medication used to treat type 2 diabetes. Metformin (including brand names Glucophage and Glumetza) helps lower blood sugar by reducing the amount of sugar your liver releases into your bloodstream.

The most common cause of type 2 diabetes mellitus is insulin resistance. Insulin is a hormone that helps lower blood glucose levels. With insulin resistance, your body doesn’t respond to insulin effectively, which causes high blood sugar levels. Metformin helps improve insulin sensitivity which helps lower blood sugar levels.

One of the benefits of metformin is that it doesn’t cause low blood sugar. That means that you can safely take metformin with other types of medication for diabetes, including insulin and sulfonylureas.

Metformin dosages range from 500 milligrams to a maximum of 2,550 milligrams per day. It’s usually recommended to split the dose among meals, typically three times per day. There is also an extended-release version of metformin that is designed to be taken once daily.

RELATED: Metformin Recall: Is Your Medication Affected?

Medications and drugs to avoid while taking metformin

Fortunately, there aren’t many serious metformin drug interactions. But taking these medications alongside metformin could lead to a serious drug interaction:

Contrast media

Also called X-ray dye or just “contrast”, this dye is injected before certain medical scans such as CTs and MRIs. Iodinated contrast dye can seriously interact with metformin so should be avoided. The use of iodinated contrast dyes increases the risk of lactic acidosis.

This interaction is very rare and would only happen if the contrast dye itself caused renal impairment (kidney damage). If contrast damages your kidneys, then they can’t clear metformin out of your system, and levels would build up and potentially cause lactic acidosis.


This is a plant native to India and Africa used in Ayurvedic medicine. Gymnema is used to treat conditions like obesity and diabetes. 

According to animal studies, Gymnema may reduce the efficacy of metformin and lead to high blood glucose levels.


This medication is a type of antibiotic to treat pink eye. It can cause both high and low blood sugar and isn’t recommended for people with diabetes.


This drug is can treat malaria. When taken together with metformin, your kidneys might not be able to clear the metformin, which can result in lactic acidosis.

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Over the counter medications to avoid while taking metformin

There aren’t any known significant metformin drug interactions for over-the-counter medications. 

You should always consult with your health care provider and/or pharmacist when you are taking other prescription medications since they might interact with over-the-counter drugs.

Potential serious side effects associated with taking metformin

Very rarely, a condition called lactic acidosis may occur while taking metformin. Lactic acidosis is a serious condition where your body creates more lactic acid than your body can clear. 

The symptoms of lactic acidosis usually set in quickly and include abdominal discomfort, fast, shallow breathing, muscle pain and cramping, and unusual fatigue.

Metformin overdose is the main risk factor for developing lactic acidosis. According to a position statement in the American Diabetes Association’s Diabetes Care, “When metformin is used as labeled, the increased risk of lactic acidosis is either zero or so close to zero that it cannot be factored into ordinary clinical decision making.”

If you have severe renal impairment or kidney disease, you might also be at greater risk of developing lactic acidosis because your kidneys can’t clear the lactic acid from your system. 


Metformin has very few drug interactions but shouldn’t be taken with iodinated contrast media, which is the most common interaction. Metformin is safe to take with most types of over-the-counter medication, but the patient should always consult with their health care provider for guidance and further medical advice if they have questions.

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  1. Misbin, Robert (2004) The Phantom of Lactic Acidosis due to Metformin in Patients With Diabetes.
  2. Gupta RC, Chang D, Nammi S, Bensoussan A, Bilinski K, Roufogalis BD. Interactions between antidiabetic drugs and herbs: an overview of mechanisms of action and clinical implications. Diabetol Metab Syndr. 2017;9:59. Published 2017.

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