How long does metformin take to lower blood sugar?

In this article:

• How fast does metformin start working?
• Effects on blood sugar and A1C
• Signs metformin is working
• Why is my blood sugar still high?
• What affects how fast metformin works
• Alternatives

In this article

• How fast does metformin start working?
• Effects on blood sugar and A1C
• Signs metformin is working
• Why is my blood sugar still high?
• What affects how fast metformin works
• Alternatives

Metformin is a first-line oral medication for the management of Type 2 diabetes, along with exercise and changes to diet. For decades, it’s been the first medication most people with Type 2 diabetes are prescribed: effective, well-studied, and inexpensive. Metformin belongs to the class of drugs known as biguanides, and is sold under brand names including Glucophage, Fortamet, and Riomet. Even as glucagon-like peptide-1 receptor agonists, or GLP-1 medications, grow more popular, metformin is still where many start. Beyond treating Type 2 diabetes, healthcare providers sometimes also prescribe it to lower blood sugar in patients with prediabetes and polycystic ovary syndrome (PCOS).

So, how soon does it work? Metformin begins lowering blood sugar within the first week of treatment, but it typically takes two to three months of consistent use to see the drug’s full effect on A1C, according to the drug’s FDA prescribing information. That’s because A1C reflects average blood sugar over the prior two to three months, so the number moves slowly even after glucose levels improve. The timeline may vary for you, based on individual factors, such as form and dose prescribed.

How fast does metformin start working?

It’s natural to be eager for your blood glucose levels to start dropping once you begin taking metformin. Metformin doesn’t lower blood sugar immediately the way a fast-acting insulin would, but it does start working to help get that process going pretty quickly, according to Shriya Gandhi, MD, an endocrinologist with UI Health in Chicago, Illinois.

“Usually, it takes about 48 hours at the outset,” Dr. Gandhi explains. “But it does start working within the first week of treatment, in terms of noticing an improvement in blood sugar. So that’s pretty quick.”

Dr. Gillian Goddard, MD, endocrinologist and adjunct assistant professor of medicine at the NYU Grossman School of Medicine, agrees, “It takes a few days for metformin to lower blood sugars, depending on whether an immediate-release formulation or an extended-release formulation is prescribed.”

A higher dose of an immediate-release formulation may initially have faster effects on blood sugar. However, many providers start with a low dose, extended-release formulation to avoid common metformin side effects, such as diarrhea, nausea, vomiting and bloating. Then, increase the dose gradually as your body gets used to the medication. Over the long term both forms take two to three months to show significant, measurable improvement on A1C tests.

Here’s what to expect on a typical timeline:

• 1-2 days: Metformin starts to reach a steady state in the body, lowering the amount of glucose produced by the liver and released into the bloodstream and increasing insulin sensitivity. That’s in contrast to fast-acting rescue medications like insulin, or oral medications like Starlix (nateglinide), that work rapidly by stimulating the pancreas to release insulin right after a meal.
• 7 days: You may notice a decrease in fasting blood sugar levels day by day.
• 60-90 days: Your healthcare provider may retest your A1C to measure the full impact of the medication over the past two to three months.

How much does metformin lower blood sugar and A1C?

Biguanides such as metformin can decrease the A1C levels of a person with Type 2 diabetes by about 1%. The exact decrease depends on your initial A1C levels and the dose prescribed.

The A1C test (also known as the hemoglobin A1C test or hbA1C test) is a blood test that gives a view of your average blood sugar levels over the previous two or three months. The typical goal for most people with Type 2 diabetes is an A1C under 7% (or less than an average blood glucose of 154 mg/dL), according to the American Diabetes Association. For comparison, a normal A1C for a person without diabetes is below 5.7%.

The effect metformin has on A1C can vary, depending on the dose that you take, according to Susan Hudec, MD, an endocrinologist and director of diabetes services at Endeavor Health. “The initial dose of 500 mg daily will typically decrease A1C around 0.5%,” she says. “The maximum dose of 2000 mg daily will decrease A1C by up to 1.5%.”

The daily dose your healthcare provider prescribes depends on how high your blood sugar levels were before starting treatment, and how your body responds to the medication. For example, if your A1C was 7.5%, then a 500 mg daily dose of metformin may help you reach your goal. If your A1C was above 8%, you may need to take 1500-2000 mg of metformin. But the dose still starts low and is increased slowly to lower the risk of side effects.

How much metformin lowers blood sugar by dose
Metformin dose	Typical effect on fasting blood sugar	Typical effect on A1C
500 mg	Lowers by ~15 to 20 mg/dL	Reductions of ~0.5% to 0.6%
1,000 mg	Lowers by ~25 to 30 mg/dL	Reductions of ~0.7% to 0.8%
1,500 mg	Lowers by ~40 to 50 mg/dL	Reductions of ~1.0% to 1.2%
2,000 mg	Lowers by ~60 to 80+ mg/dL	Reductions of ~1.2% to 1.5%

What are the signs metformin is working?

The evidence that metformin is working is a drop in your blood sugar levels and an eventual decrease in your hemoglobin A1C.

You may or may not notice any obvious signs that metformin is working. “You might notice your thirst decreases or your hunger decreases as your sugars go down,” Dr. Gandhi says.

In addition to reduced thirst and a reduced need to urinate, the most common signs that this medication is working include:

• Increase in energy
• Possible mild weight loss
• Fewer cravings for sugar and carbohydrates.

However, many people don’t notice any physical  signs that metformin is working. You may only see the difference in your daily blood sugar levels, or when your provider retests your A1C.

Why is my blood sugar still high after taking metformin?

Metformin doesn’t work for everyone.  “There are a lot of reasons that medication might be ineffective,” Dr. Hudec says. The most common include:

• You didn’t make dietary changes: “ If you have ice cream or sweets every day or every meal, glucose will likely remain above goal even with metformin therapy,” says Dr. Hudec.
• You need a higher dose: For example, if you’re taking 500 mg per day, your provider might increase your dose to 1000 mg daily. But that only works up to a certain point.
• You need a second medication: “Potentially, the patient has some component of insulin deficiency, so an insulin sensitizer alone will not bring their glucose to goal,” Dr. Hudec explains. Dr. Gandhi might suggest adding a sodium-glucose cotransporter 2 inhibitor (or SGLT2 inhibitor), or even a GLP-1 medication to reduce blood sugar further.

You should never take an extra pill of metformin if your blood sugar is still high.“This is not something we would typically recommend,” Dr. Goddard says. “Metformin is excellent at lowering blood sugar in the long run but isn’t so effective at lowering blood sugar right after taking it. Taking too much metformin can put you at risk for lactic acidosis, which can be dangerous. You should only adjust your metformin dose in consultation with your doctor.”

Metformin-associated lactic acidosis, which occurs when lactic acid builds up to dangerous levels in the blood, is rare but requires emergency medical treatment.  Signs include an upset stomach with symptoms such as nausea and vomiting, stomach pain, myalgia, dizziness, a feeling of coldness in your extremities, and even the possible loss of consciousness.

What affects how quickly metformin works?

“The main factor affecting how quickly a medication works is its half-life. That is, how long the medication stays in the blood,” Dr. Goddard says. “Medications with a shorter half-life start working faster. Thus, immediate-release metformin will start working faster than extended-release metformin.”

However, because metformin can cause some gastrointestinal (GI) side effects, she typically recommends starting with a lower dose or using an extended-release version. It may take longer to kick in, but it reduces side effects. You may need to give it some time to start working, so don’t stop taking it without consulting your healthcare provider. While taking metformin on an empty stomach may mean the pill is absorbed more quickly, it doesn’t translate to reducing blood sugar more effectively. It only increases the risk of stomach-related side effects. What you eat while taking metformin doesn’t affect how quickly it works, but eating high-sugar, high-carbohydrate, and processed foods can counteract the benefits of the treatment by promoting weight gain and blood sugar spikes.

Should I switch to a metformin alternative?

Your healthcare provider may suggest a metformin alternative if you:

• Experience unbearable side effects that don’t go away, such as diarrhea, vomiting, or dehydration
• Continue to have high blood sugar levels even after taking metformin for some time and increasing the dosage
• Have a coexisting condition that is better treated by another medication class, such as obesity
• Have a coexisting condition that is contraindicated for metformin, such as kidney disease or congestive heart failure

In these cases, your provider may switch you to one of the following medication classes:

• Glucagon-like peptide-1 receptor agonist (GLP-1 RA), such as Ozempic (semaglutide), Victoza (liraglutide), Trulicity (dulaglutide), and Mounjaro (tirzepatide)
• Sodium-glucose cotransporter 2 inhibitor (SGLT-2 inhibitor), which include medications such as Jardiance (empagliflozin), Farxiga (dapagliflozin), Invokana (canagliflozin), Steglatro (ertugliflozin), and Brenzavvy (bexagliflozin)
• Dipeptidyl peptidase-4 (DPP-4) inhibitor, which includes Januvia (sitagliptin), Tradjenta (linagliptin), Onglyza (saxagliptin), and alogliptin
• Sulfonylurea, such as Glucotrol XL (glipizide ER)
• Thiazolidinedione, such as Actos (pioglitazone)
• Add a long-acting or short-acting insulin

“It’s a great medication, but it’s not for everyone,” Dr. Gandhi says. Talk to your provider; there are many other options if metformin doesn’t work for you.