What Are the Signs Metformin Is Not Working? What to Look Out For

By Craig Sorkin, DNP, APN
Medically reviewed checkmarkMedically reviewed
July 11, 2022

Metformin is one of the most common diabetes medications.

However, not everyone with diabetes responds to the medication.

In other cases, it may work for a while and then become less effective at managing high blood sugar levels.

If metformin stops working, a medical provider may add another diabetes medication to provide more support, or they may prescribe a different medicine.

In this article, we’ll explore signs that metformin is not working as it should, as well as what to do if it is not.

We’ll also discuss common side effects and when to see a healthcare provider.

Signs Metformin Is Not Working

Although metformin is highly effective at controlling blood glucose, it may work less effectively over time.

If you notice any of the following symptoms while taking metformin, talk to a healthcare provider.

The medication may not be working for you.

  • High blood sugar levels: This is usually the first sign that metformin is not working as it should. Blood glucose levels should be less than 100 mg/DL when fasting and less than 140 mg/DL after meals. However, the appropriate diet is important to controlling glucose as well. 
  • Elevated hemoglobin A1C: Blood work can check if your hemoglobin A1C is higher than it used to be or out of range. The hemoglobin A1c is an average glucose over 3 months time. 
  • Frequent urination: As glucose levels rise, the body eliminates more glucose via the kidneys. As this happens, you may need to pee more often.
  • Increased hunger or thirst: Increased urination can disrupt levels of electrolytes and body fluids. This can result in symptoms such as excess hunger or thirst.
  • Fatigue: Glucose is needed for energy in the body, but highly elevated blood sugar levels can increase fatigue. This is most likely as the body is not able to process the glucose effectively, if at all.

Keep in mind, these signs do not necessarily indicate that metformin is not working.

They could also mean:

  • Your diet has changed.
  • You are being less physically active or are not getting enough exercise.
  • You have gained weight.
  • You are not taking the medication properly.

Have questions about Metformin? Chat with a provider through K Health.

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Why Metformin Failure Is a Concern

With type 2 diabetes, if blood glucose becomes harder to control or is not kept within range due to metformin failure, it can lead to serious health complications in the short and long term such as:

  • Hypertension (high blood pressure)
  • Stroke
  • Coronary artery disease
  • Peripheral artery disease
  • Chronic kidney disease (CKD)
  • Cataracts
  • Glaucoma
  • Diabetic retinopathy (eye problems caused by diabetes)
  • Diabetic neuropathy (nerve problems caused by diabetes)
  • Diabetic nephropathy (kidney problems caused by diabetes)

How long does metformin take to work?

Metformin changes the way that the liver makes glucose, which takes time.

Metformin starts working 48 hours after you begin taking it; however, the full effects do not start to kick in until after 4-5 days

Does metformin lose effectiveness over time?

You may need to increase metformin dosage over time to properly control glucose levels.

This can happen for a few reasons:

  • Diet and lifestyle are not supporting glucose balance, requiring more medication to offset them. Keep in mind that metformin is designed to work with diet, exercise, and lifestyle changes, not to replace them.
  • Diabetes is a chronic condition that may worsen over time based on other health factors, including age.
  • Liver or kidney problems can change the way that the body uses medication, which can alter how effective metformin is.

There are other reasons why metformin may be less effective.

A medical provider can assess whether it’s best to add another medication or try a different drug.

What to Do If Metformin Isn’t Working

If metformin is not controlling blood glucose levels as expected, some changes may help:

  • If you recently started taking metformin, you may need to wait longer for it to fully take effect. If you’ve been on metformin for at least three months talk to your medical provider. They may need to increase your dosage, or you may not be taking the medicine correctly.
  • If you are not taking your medication regularly because of side effects, tell your medical provider. They can change your dosage, switch you to the extended-release form of metformin, or recommend a different medication.
  • If you have been taking metformin for many years and notice your blood glucose or hemoglobin A1C levels rising, you may need another medication or an increase in dosage. Diabetes can progress, even when you are doing everything you can to manage it.

How to check if metformin is working

A medical provider can run a few tests to see how metformin is affecting your health:

  • Blood work can check if your glucose, insulin, and HbA1C levels are in range. If they are, the medication is working.
  • If your medical provider suspects that you are not tolerating metformin or you are experiencing side effects, they may test your vitamin B12 levels. Metformin can make it harder to absorb this nutrient, leading to a vitamin B12 deficiency. This can cause anemia.

Blood sugar goals

Your medical provider will tell you what your blood sugar target range should be.

For most people who have type 2 diabetes, the target for hemoglobin A1C is 7% or less.

Metformin Side Effects

Metformin may cause the following side effects. Many of these resolve as your body adjusts to the medication.

In some cases, metformin can cause more serious side effects, like B12 deficiency or anemia. 

Serious, potentially life-threatening lactic acidosis can occur if too much metformin builds up in the body.

If you notice sudden flushing, feelings of warmth, dizziness, nausea, or vomiting or generally feel unwell, tell your medical provider and seek emergency medical care.

Lactic acidosis can be fatal if not treated promptly.

Have questions about Metformin? Chat with a provider through K Health.

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When to See a Medical Provider

See your healthcare provider if you take metformin and notice that your blood glucose levels are not as controlled as they should be.

If you are concerned about taking metformin or worried that it is not working, they can perform lab tests and other assessments to determine the best course of care.

How K Health Can Help

Did you know you can access online urgent care with K Health?

Check your symptoms, explore conditions and treatments, and if needed, text with a healthcare provider in minutes. 

K Health’s AI-powered app is HIPAA compliant and is based on 20 years of clinical data.

Frequently Asked Questions

What happens when metformin doesn't work?
If metformin does not work, your blood glucose levels and hemoglobin A1C levels will increase. You may also develop symptoms of hyperglycemia. Your healthcare provider may increase your dosage or add another medication to better manage your blood glucose.
What should I avoid while taking metformin?
If you take metformin, avoid the following medications and supplements: beta blockers, cimetidine, calcium channel blockers, chromium, coenzyme Q10, corticosteroids, diuretics, digoxin, dofetilide, estrogens, garlic, green tea, morphine, oral contraceptives, phenytoin, phenothiazines, procainamide, quinidine, ranitidine, sympathomimetics, triamterene, and vancomycin.
Why is my blood sugar high even with medication?
If your blood sugar is high despite medication, it could mean a few things: Your dosage is not high enough, you are not responding to the medication as expected, or your diet, exercise, and lifestyle are not helping enough to control your blood sugar.
What should your blood sugar be when on metformin?
Once metformin has started to work, it should help keep your blood glucose levels in the normal range. This means fasting glucose of 100 mg/dL or lower and post-meal levels of 140 mg/dL or lower.
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Craig Sorkin, DNP, APN

Craig Sorkin, DNP, APN is a board certified Family Nurse Practitioner with over 15 years experience. He received his Undergraduate and Graduate degrees from William Paterson University and his doctoral degree from Drexel University. He has spent his career working in the Emergency Room and Primary Care. The last 6 years of his career have been dedicated to the field of digital medicine. He has created departments geared towards this specialized practice as well as written blogs and a book about the topic.