What are the Signs Metformin is Not Working? Things to Look Out For

Can Metformin stop working? Knowing the signs Metformin is not working and what you can do about it is essential for those taking this drug.

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Written by Nazar Hembara, PhD

Published 20 May 2024

Metformin is a popular drug to treat people who have high blood sugar levels, linked to type-2 diabetes. Though generally effective, there are some cases where metformin does not work as it should and this can be caused by a multitude of reasons.

In this article, we will discuss what metformin is, how it works, its uses, the signs to look out for if the drug is not working, and how to test it. In addition, we will also outline the alternatives to metformin and who they might be suitable for.

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What is Metformin?

Metformin is used to treat high blood sugar levels caused by type-2 diabetes (mellitus), sometimes referred to as sugar diabetes. This type of diabetes affects the insulin that the pancreas produces, preventing the sugar from effectively reaching the cells within the body where it is needed. It often affects people who are overweight, but not always.

Metformin can also be used to treat polycystic ovary syndrome (PCOS), a common problem that affects women of childbearing age. This can prevent women from ovulating, can produce high levels of androgens, and cause numerous small cysts to develop on the ovaries.

How Metformin works

Metformin works by lowering blood glucose levels. This is achieved by limiting how much glucose is produced by the liver, lowering the amount of sugar absorbed by the intestines, and also assisting the body’s cells to absorb more glucose from the bloodstream. Additionally, this medication improves how the body responds to the hormone insulin.

Metformin can usually be taken alongside other diabetes medication, including insulin.

How long does Metformin take to work?

Typically, it will take an individual around four-to-five days to experience the benefits of their metformin dosage. However, this can differ from person to person, with the speed of effectiveness often varying between children and an overweight adult, for example.

How do you know if Metformin is not working?

In some cases, metformin may not work for certain individuals and there are 7 key signs that a person should look out for before consulting their healthcare provider.

High blood sugar levels

An obvious sign that metformin is not working is if your blood sugar levels remain high when testing. Blood glucose levels should be below 100 mg/DL (decilitre) when fasting and less than 140 mg/ DL after a meal. However, metformin may seem like it is not working if a person is not maintaining a healthy diet which can be equally as important in controlling blood sugar levels.

Elevated hemoglobin A1C

Elevated levels of hemoglobin A1C are another telltale sign that metformin may not be working. When tested, hemoglobin A1C should be below 5.7%, from 5.7% to 6.4% is an indication of pre-diabetes, and above 6.5% is out of range.

Frequent urination

If glucose levels remain high or continue to rise then the body needs to remove excess glucose via the kidneys, increasing the need to urinate more.

Increased hunger or thirst

Urinating more also has a knock-on effect on other parts of the body, causing disruption in terms of your overall bodily fluids and electrolytes. This results in symptoms such as feeling hungry or thirsty on a regular basis.


Glucose gives the body energy but if glucose levels in the blood are elevated above normal levels then it can have an adverse effect, causing a person to feel fatigued. This is because there is too much glucose for the body to process properly, meaning only minimal levels are reaching the cells where it is needed.

Blurred vision

Blurry vision is another side effect of high blood glucose levels, heavily hinting that the medication you are using is ineffective.


High blood sugar is medically known as hyperglycemia and occurs when the body does not have enough insulin, or if it does not process insulin properly. If metformin doesn’t work or stops working then signs of hyperglycemia can return, causing symptoms such as headaches, nausea, and vomiting, as well as some symptoms mentioned above such as blurred vision.

Why does Metformin stop working?

There are several reasons why metformin may stop working and it is not always a case of the drug’s effects waning. Below are some of the main causes why metformin, but also other diabetes drugs might lose their efficacy.

Change in diet

Changing your diet or general eating habits can also cause metformin to lose its effectiveness. A person suffering from diabetes is advised to maintain a balanced diet and to cut out some of the more unhealthy food groups where possible. If this change in eating habits is sudden, then it may have an adverse, short-term effect.


Exercise is highly recommended to help improve a person’s health, especially a person who has diabetes. However, this can also impact blood glucose levels which can have implications in terms of the effectiveness of drugs such as metformin. In fact, there is evidence that exercising can have a direct impact on how well metformin works. 

Weight gain

Metformin can sometimes cause some weight loss if taken for a period of several months or more, although it is not designed as a weight loss medication. However, if you gain weight since you first began taking metformin then it could suggest that your current dosage is not adequate. If this is the case then you should consult with your doctor and discuss upping your dosage to see if your weight gain subsides.

You are not taking the medication properly

For any medication to be effective, the right dose needs to be taken or it will not work as well as it should. Always ensure you are taking the Metformin dosage that has been prescribed and if you notice any of the signs that it may not be working you should inform your doctor.

What to do if Metformin isn’t working

If you identify the signs that metformin is not working effectively there are several things you could do:

  • The first step that should be taken is to contact your doctor or healthcare provider and inform them of the signs that your medication is not working.
  • If you have only just started taking metformin then it is advised to wait a while longer for the medication to take full effect. However, if you have noticed no improvement over several months then you should speak with your doctor about increasing your dosage.
  • If metformin has given you unwanted side effects which have forced you to stop taking the correct dosage on a regular basis, then you should discuss a different dosage or an alternative medication.
  • If you have been taking metformin for a number of years and you suddenly notice a rise in blood sugar levels or hemoglobin A1C then your dosage may need to be increased, or it could be time to discuss trying a different medication with your doctor. This could be a sign that your diabetes has progressed, even though you have taken the necessary steps to manage the condition.

Natural diabetes management tips to adopt when Metformin stops working

If metformin stops working then an alternative medication or higher dose is not always the answer. In some cases, there are some natural diabetes management techniques that can improve the efficacy of metformin to deliver the desired results.

  • Aiming for a suitable level of weight loss is highly advised when taking diabetes medication.
  • Try to build your diet around healthy plant-based food.
  • Maintain a blood-sugar-friendly diet, avoiding things like full-sugar soda, chocolate, sweets, and other items that contain excess sugar.
  • Exercise daily, even if it is just mild physical activity such as taking regular walks.

How to check if Metformin is working

Blood work tests can check the levels of glucose, insulin, and hemoglobin A1C in the body and are the best ways to check if metformin is working or not.

If your doctor perceives that your body has a low tolerance to metformin or the side effects are too extreme then they may also test your vitamin B12 levels. This is because metformin can make it difficult to absorb B12 sufficiently, causing a deficiency. This could cause a person to become anemic.

Why Metformin failure is a concern

Metformin failure can be concerning for a number of reasons, possibly suggesting a person is suffering from another disease or condition that is stopping the medication from working how it should.

Causes for concern could include:

  • Reduced blood flow increases the chances of suffering a stroke.
  • A narrowing of the arteries to the heart which could signal coronary heart disease.
  • A narrowing of the arteries to the heart of the brain could also lead to peripheral artery disease.
  • A progressive decline in kidney function could indicate chronic kidney disease.
  • Eye damage that is related to diabetes could result in diabetic retinopathy.
  • Diabetes nerve-related pain could point to diabetic neuropathy.
  • Glaucoma could develop, an eye issue linked to optic nerve damage.
  • Cataracts could also develop which is the clouding of the eye lens, impairing a person’s vision.

What are the alternatives to Metformin?

Alternatives to metformin include SGLT-2 Inhibitors such as Invokana, Farxiga, Jardiance, Steglatro, or GLP-1 Receptor Agonists like Bydureon, Byetta, Ozempic, Adlyxin, Rybelsus, Trulicity, and Victoza.

The drug, Glipizide, also helps to treat high blood sugar levels caused by type 2 diabetes. This medication belongs to the class of drugs called sulfonylureas. It works by managing the release of insulin from the pancreas and directing how blood sugar is stored.

The bottom line

Metformin is an effective medication to treat type-2 diabetes, however, in some cases, the drug may not work, with blood sugar levels remaining high or continuing to increase. This could be caused by a number of reasons, including weight gain, exercise, or a change in diet.

If metformin is ineffective then there are a number of signs to look out for such as fatigue, regularly feeling hungry or thirsty, blurred vision, and continued high levels of glucose or hemoglobin A1C in the blood.

If you feel that metformin is not working and you experience any of the signs above then you should consult with a healthcare professional to discuss increasing your dosage or possibly changing medication.

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