Metformin: Drug Interactions & Side Effects

Instructor: Adrianne Baron

Adrianne has a master's degree in cancer biology and has taught high school and college biology.

This lesson is going to give a detailed look at the most common side effects associated with the diabetes drug metformin. We will also discuss the biggest concerns for drug interactions.


You are in to see Dr. Patrick for your annual physical. He notices that your type 2 diabetes is not as well controlled as it was before. Type 2 diabetes is a condition in which your body does not have enough insulin in the bloodstream due to ineffective metabolic processes. You were diagnosed with this condition about 7 years ago. The diet and exercise routine that was helping you to maintain an appropriate blood sugar level is just not enough anymore.

Metformin is used to treat type 2 diabetes
Picture of metformin pack

Dr. Patrick prescribes metformin, a medication that reduces the amount of sugar that you absorb from the foods that you eat. It also helps to reduce blood sugar by decreasing how much sugar is released into the bloodstream by the liver. You are okay with starting this medication, but you are concerned because you keep hearing about all of these horrible side effects that come with the use of some prescription medications.

Side Effects

Yes, there are some side effects that are seen with this drug. Dr. Patrick informs you that the most common side effects are not very severe. As a matter of fact, he lets you know that they are a lot like a very bad case of ingestion. You may notice that you have more gas than usual, are bloated, feel heartburn, and have mild stomach pain.

Stomach pain is a side effect of metformin
Drawing of stomach pain

Other common, but not very serious side effects, are headache and muscle pain. You can also have the unpleasant side effects of being at one or the other end of the spectrum of constipation and diarrhea.

Dr. Patrick says that he does need to go over the more severe side effects that require immediate medical attention if they occur. Any signs of an allergic reaction including hives and itching or of a more severe, life-threatening allergic reaction, such as difficulty breathing, will require a trip to the ER.

The other main concern and set of possible side effects seen with metformin are those that occur as a result of an overdose. Dr. Patrick says that an overdose of metformin will cause hypoglycemia, which is low blood sugar. This is a life-threatening condition. He says that if you have a rapid or slow heartbeat, nausea, vomiting, decrease in appetite, lightheadedness, dizziness, feel cold, and experience deep, rapid breathing, or shortness of breath, you need to report to the ER immediately for treatment of metformin overdose.

On very rare occasions, metformin has been known to cause a condition called lactic acidosis. Dr. Patrick discusses that this is a condition of excessive lactic acid in the bloodstream. It is life-threatening because it usually only occurs due to a drastic decrease in oxygen in the bloodstream.

Drug Interactions

Do you remember learning about chemicals in school? Did you have the experience of you or someone else mixing two chemicals that caused some weird or huge reaction that was very active? Well that same thing can happen in your body. Maybe not on the same scale, but keep in mind that all drugs are composed of chemicals and chemicals can react!

For that reason, there are some drugs that may interact with metformin and either enhance its action or reverse its action. You learn from Dr. Patrick that some medications cause an increase in blood sugar levels and, when they are taken with metformin, blood sugar levels may spiral out of control. Some examples of medications that increase blood sugar levels include estrogen, water pills, calcium channel blockers, birth control pills, isoniazid, corticosteroids, and nicotinic acid.

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