When you start taking metformin, it can take a while to see any positive change in blood sugar levels or weight. 

If you’ve recently added this medication to your daily routine, you may be anxious to see results, and fast. 

This article will investigate how you will know if your metformin is or isn’t working, and what you can do about it. 

Close-up of metformin pill

Key Points:

  • Metformin’s effectiveness is primarily indicated by lower blood sugar levels, reduced HbA1c levels, and in some cases, modest weight loss. These changes might take several months to become noticeable.
  • Persistent high blood sugar levels, no improvement in HbA1c after several months, and lack of weight loss (or weight gain) despite a healthy lifestyle may signal that metformin isn’t working effectively.
  • Common side effects of metformin, such as nausea, diarrhea, and a metallic taste in the mouth, usually subside within a few weeks. Severe side effects or prolonged discomfort should be discussed with a healthcare provider.
  • If metformin is not suitable, alternative medicines include insulin therapy, SGLT-2 inhibitors, GLP-1 receptor agonists, and others. It’s crucial to consult a healthcare provider before making any changes to medication regimens.

Table of Contents

Why do people take metformin? 

Metformin is a first-line therapy for prediabetes (a condition in which blood glucose levels are high, but not in the range for a diabetes diagnosis) and type 2 diabetes. 

Metformin functions by decreasing glucose production in the liver, minimizing glucose absorption in the intestines, and enhancing the efficiency of the body’s own insulin. This results in a reduction of blood sugar levels.

The American Diabetes Association (ADA) recommends metformin for people who have:

  • prediabetes between the ages of 25 and 59 years old
  • an HbA1c level (a measure of glucose control over the previous 2 to 3 months) of 6% or higher
  • a BMI (body-mass index, a measure of weight relative to height) of 35 or higher
  • fasting plasma glucose (fasting at least 8 hours) of 110 mg/dL or higher
  • a prior gestational diabetes diagnosis (a type of diabetes that occurs during pregnancy)
  • a type 2 diabetes diagnosis

Taking metformin regularly can help improve insulin sensitivity, reduce appetite, lower blood sugar, and decrease HbA1c levels, and can even help people lose a modest amount of weight when used in conjunction with a healthy diet and regular physical activity. 

Side effects of metformin 

Experiencing side effects of any new drug, including metformin, is extremely common. Most of these side effects are minor and subside within a few weeks of taking the medication. 

Experiencing side effects is not an indication that your metformin is not working. 

Be vigilant for the following symptoms and contact your doctor if they worsen or do not go away on their own within a few weeks: 

  • Nausea
  • Vomiting 
  • Diarrhea
  • Decreased appetite 
  • Weight loss 
  • Low blood sugar (especially if you also take insulin)
  • A metallic taste in your mouth 
  • Heartburn
  • Bloating
  • Gas
  • Constipation
  • Stomach pain

Seek emergency medical attention if you’re experiencing severe nausea and have low blood sugar, and you cannot keep anything down with which to treat it.

You can learn more in our guide Metformin Side Effects: What You Need to Know.

Signs metformin is working

There are a few signs that your metformin is working. The effects of the medication may build over time, so do not worry if you do not see immediate results.

Lower blood sugar levels

If you check your blood sugars regularly at home, you may notice that your blood sugar levels are consistently lower once you start taking metformin. This may be particularly true after eating, when you may be used to elevated levels. 

“With my CGM [continuous glucose monitor] data, I can see quite clearly that my blood sugar is more responsive to insulin. Instead of fighting to chase a high for hours that I didn’t bolus appropriately for, I can usually head it off within a reasonable time frame. Also, I have fewer spikes in general.”

Kat Schroeder, T1D metformin user (read about Kat’s experience with metformin)

Lower HbA1c level

If you do not check your blood sugar levels at home, you can contact your doctor’s office after a few months on metformin so they can run an Hba1c test, which measures your average glucose control over the previous 2 to 3 months. 

Your HbA1c should be lower after a few months on metformin. If not, discuss alternative medications to metformin and/or lifestyle changes with your doctor. 

You can also measure your HbA1c at home with a simple test kit you can buy at your local pharmacy or online. 

You’ve lost some weight 

Additionally, you may notice that you’re losing some weight, especially if you’re taking metformin in conjunction with adopting a healthy diet and increased physical activity. However, weight loss is often modest and can be inconsistent. 

Signs metformin is not working

If you’ve been taking metformin for a month or more and notice the following symptoms, it can be a sign that metformin is not working. 

In this case, you may need to either increase your dose, work with your doctor to experiment with combination drugs, or seek an alternative medication. 

Keep a watch out for the following signs:

Your blood sugar levels have remained stubbornly high 

If your blood sugars continue to spike after meals, or you have been routinely waking up with high blood sugar levels despite taking metformin, it may be a sign that the medicine isn’t working and you should call your doctor. 

It’s easiest to track your daily blood sugar levels if you have an at-home blood glucose meter or a continuous glucose monitor (CGM). 

Your HbA1c level has not improved

Most likely, your baseline HbA1c level before starting treatment was higher than your target range. If after some time on metformin (usually 3 months) it hasn’t budged, this is a sign that metformin is not reliably bringing your blood sugar levels down. 

It’s important to be aware of the signs of high blood sugar. These include:

  • Increased hunger
  • Increased thirst
  • Blurry vision
  • Increased and frequent urination 
  • Fatigue
  • Lethargy
  • Muscle aches
  • Headache
  • Fruity-smelling breath 
  • Weight loss (which may be confused with metformin working, but is also a sign of dangerously high blood sugar levels) 

You’re not losing weight or you’ve gained weight 

Metformin doesn’t cause weight loss in everyone who takes it, but many people do enjoy modest weight loss (less than 10 pounds) after taking the medication for several months. 

However, if you’re eating healthy and exercising regularly along with taking metformin, but your weight hasn’t budged or you’ve gained weight, this could be a sign that you may need to increase your dose or seek an alternative. This may be a sign that you need to contact your doctor. 

Frequently asked questions

How long does metformin take to work? 

The medication needs time to build up in your system, and oftentimes, your doctor will start you on a low dose to avoid uncomfortable side effects.

Do not expect a miracle within the first week of treatment. That said, after a few weeks, you should start to notice lower blood sugar levels, especially after meals.

Any weight loss and improvements in HbA1c levels, however, may take several months of taking metformin at your full dose. 

How long should I be on metformin before giving up? 

Don’t stop taking metformin before it has a chance to fully work in your body, which can take up to several months. 

Also, never stop taking a prescribed medication before talking with your doctor. Quitting any drug cold turkey can cause unpleasant side effects, so weaning under the guidance of your doctor is key. 

How can I maximize the benefits of metformin? 

Metformin by itself is not a miracle drug. To enjoy the maximum benefits from the medication, it is best combined with healthy eating and regular physical activity.

Work with your doctor or a registered dietitian (RD) to develop a meal plan and set of healthy activities that you can fit into your lifestyle.

The U.S. Centers for Disease Control and Prevention (CDC) recommends that most adults target at least 150 minutes of moderate exercise weekly, averaging about 30 minutes a day. This can include activities like walking, jogging, swimming, or cycling. 

Additionally, they recommend incorporating muscle-strengthening exercises, such as weightlifting, at least twice a week.

Does metformin become less effective over time?

Your dose of metformin may need to be increased over time to continue effectively managing your blood glucose levels. This can be due to a variety of factors. For instance:

  • If your diet and lifestyle habits are not able to sufficiently help manage your blood sugar levels, a higher dose might be required. It’s important to remember that metformin is intended to complement, not replace, healthy eating, exercise, and other lifestyle modifications.
  • Diabetes is a progressive condition, so its severity can increase over time due to various health factors, including aging.
  • Changes in liver or kidney function can affect how the body processes medications, potentially impacting metformin’s effectiveness.

In such cases, a healthcare provider can evaluate whether introducing an additional medication or switching to a different treatment might be more beneficial.

What are the alternatives to metformin? 

If metformin truly isn’t working for you, there are alternatives. For some people with unmanaged blood sugar levels, starting insulin therapy may be a more suitable option.

Metformin combination drugs, which combine metformin with another medicine, may be another option for people who find metformin alone isn’t adequately managing their blood sugar levels.

Additional drug classes available for the treatment of type 2 diabetes in the United States include:

Sulfonylureas

  • Glipizide (brand name Glucotrol)
  • Glimepiride (Amaryl)
  • Glyburide (Diabeta, Glynase)

Meglitinides

  • Repaglinide (Prandin)
  • Nateglinide (Starlix)

Thiazolidinediones

  • Pioglitazone (Actos)
  • Rosiglitazone (Avandia)

DPP-4 Inhibitors

  • Sitagliptin (Januvia)
  • Saxagliptin (Onglyza)
  • Linagliptin (Tradjenta)
  • Alogliptin (Nesina)

GLP-1 Receptor Agonists

GIP/GLP-1 receptor agonist

SGLT2 Inhibitors

Alpha-Glucosidase Inhibitors

  • Precose (generic only)
  • Miglitol (Glyset)

Finally, if you’re experiencing low blood sugar levels or don’t feel well on metformin, you may be able to wean yourself completely off the medication without starting anything new. Talk to your doctor to learn more. 

Final thoughts

Millions of people rely on metformin, an affordable and widely available medication, for improved blood sugar control. 

It’s crucial to monitor any side effects and document your experience to determine whether the medication is or isn’t working for you. 

If you encounter ongoing uncomfortable side effects or if the desired results are not achieved after a few weeks, it’s important to speak up. Remember, there are alternative treatments that might work better for you and your health goals.