Mounjaro vs. Metformin: 9 Differences You Should Know

The oral medication metformin has been a mainstay when it comes to treating Type 2 diabetes for decades. But in recent years, several injectable medications, such as Mounjaro (tirzepatide), have entered the playing field. This has left many people wondering if these new medications are a better choice.

Both Mounjaro and metformin can be effective treatments. But, while they both lower blood glucose (sugar), they do it in different ways. And there are differences when it comes to potential weight loss, dosing instructions, and side effects, too. Some of these distinctions may determine why a healthcare provider prescribes one over the other.

Let’s be clear — the “best” diabetes medication is different for everyone. But it never hurts to review your options with your provider. Here are nine differences between Mounjaro and metformin, and times when one might be a better option.

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1. Metformin is a more common first-choice medication than Mounjaro

Metformin remains the go-to choice for many healthcare providers when prescribing a Type 2 diabetes medication. And for good reason — it works and is cost-effective.

Metformin effectively lowers hemoglobin A1C (HbA1C or A1C). Your A1C represents your average blood glucose over 3 months. Metformin may also help lower the risk of heart-related problems, such as heart attacks. What’s more, there are lower-cost generic versions available.

Mounjaro also helps lower A1C. But whether it has heart-related benefits is still being studied. And it’s currently available only as a brand-name medication. Where Mounjaro really stands out from metformin is its potential weight loss benefit (more details on this below).

Your provider will take multiple factors into account when selecting the right diabetes medication for you. But if weight management is part of your diabetes treatment plan, your provider may recommend Mounjaro.

2. Mounjaro and metformin work differently to lower blood glucose

Mounjaro belongs to a group of medications with a very long name: dual glucagon-like peptide-1 (GLP-1)/glucose-dependent insulinotropic polypeptide (GIP) agonists. It acts like GLP-1 and GIP, two gut hormones found naturally in the body. These hormones play a role in digestion, appetite, and blood glucose regulation.

Mounjaro signals the pancreas to release insulin after eating. It also stops your liver from making glucose and slows the passage of food through the gut. These actions help lower blood glucose. Mounjaro is also thought to target areas of the brain that regulate appetite and fullness, which can contribute to its weight loss benefits.

Metformin is a biguanide. Similarly to Mounjaro, it lowers the amount of glucose your liver makes. But that’s where the similarities stop when it comes to how they work. Metformin doesn’t tell your pancreas to release insulin. Instead, it makes your body more sensitive to the insulin you make naturally. It also lowers the amount of glucose you absorb from the food you eat.

For some people, either Mounjaro or metformin work well enough by themselves. But because they work in two different ways, they can be combined for additional blood glucose improvement. So it’s possible you could take both Mounjaro and metformin.

3. Mounjaro and metformin are taken differently

How you take Mounjaro and metformin is one of the most obvious differences between them. Mounjaro comes as a once-weekly injection. Metformin is an oral medication that comes in pill and liquid forms. It’s usually taken once or twice a day.

This difference in dosage forms can sometimes be a deciding factor. Mounjaro can be more convenient, since you take it only once a week. But some people may be nervous about giving themselves a shot. For them, an oral medication such as metformin may be easier.

Be sure to discuss your preferences with your healthcare provider. No matter which you take, Mounjaro and metformin work best when you take them consistently. For this reason, it’s important that your provider knows if a certain dosage form is a better fit for your lifestyle.

4. Mounjaro may provide greater A1C reduction than metformin

Both Mounjaro and metformin are good at lowering A1C. The two medications haven’t been directly compared to each other in studies. But individual study data suggests that Mounjaro may provide better A1C reduction than metformin.

In initial clinical trials, Mounjaro lowered A1C by about 2% on average. Additionally, about 90% of study participants were able to get their A1C under 7% (a typical goal for many people with Type 2 diabetes). On the flip side, metformin typically provides an average A1C reduction of 1% to 1.5%.

So while both work well, Mounjaro may work a little bit better.

5. Mounjaro can result in greater weight loss than metformin

Mounjaro’s weight loss potential is often the reason it makes headlines. In fact, it’s so effective when it comes to weight loss that it’s likely to be FDA-approved for this use in the near future.

Of the current diabetes medications available, Mounjaro appears to provide the greatest body weight reduction. In clinical trials, people with Type 2 diabetes and overweight or obesity experienced an average of about a 15% reduction in body weight with the highest dose of Mounjaro.

Metformin, on the other hand, is considered a “weight-neutral” diabetes medication. It may not cause body weight changes for most people who take it. But for some people, it can provide a modest weight loss. In some studies, people taking metformin for a year have noted up to a 6 lb weight loss.

6. Metformin is approved for use in children, but Mounjaro is approved only for adults

Metformin is FDA-approved for Type 2 diabetes in both adults and children. In fact, it can be given to kids as young as 10 years old. It’s one of a few oral diabetes medications approved for kids. But it tends to be the treatment of choice for most children with Type 2 diabetes.

Mounjaro is currently approved only for use in adults. There is an ongoing clinical trial studying its safety and effectiveness in children 10 years and older. But results aren’t expected until 2025. So it may be some time before Mounjaro is approved for kids.

7. Mounjaro and metformin have unique risks

Mounjaro and metformin share some common side effects. Both tend to cause gastrointestinal side effects for many people. This is especially true when you start treatment or shortly after raising the dose.

Common side effects of both Mounjaro and metformin include:

• Nausea

• Diarrhea

• Vomiting

• Stomach pain or discomfort

Both Mounjaro and metformin have a low risk of hypoglycemia (low blood glucose). This risk goes up if you’re also taking insulin or medications that cause your body to release insulin. These include sulfonylureas, such as glipizide, and glinides, such as repaglinide.

When taken long term, metformin can lower vitamin B-12 levels. This can lead to anemia (low red blood cells). Metformin also has a risk of lactic acidosis. This side effect is extremely rare but can be life-threatening.

In comparison, Mounjaro has been linked to pancreatitis (inflammation of the pancreas) and gallbladder disease. It may also raise the risk of thyroid cancers when taken long term. These side effects are all very rare. But if you have a history of these conditions, Mounjaro might not be right for you.

Keep in mind: These aren’t the only possible side effects for either Mounjaro or metformin. Please discuss the risks of these medications with your healthcare provider and pharmacist for more details.

8. Metformin is available in combination pills with other diabetes medications

There are many combination diabetes medications available. Since it’s prescribed so frequently, metformin is a common medication included in these combination pills. These products can help lower the number of pills you take in a day. This can make it easier to remember your pills and stick to your medication regimen.

Examples of combination pills that include metformin include:

• Glyburide / metformin

• Janumet and Janumet XR (sitagliptin / metformin)

• Synjardy and Synjardy XR (empagliflozin / metformin)

• Jentadueto and Jentadueto XR (linagliptin / metformin)

Mounjaro’s active ingredient, tirzepatide, isn’t included in any combination products right now. But given how new Mounjaro is compared with metformin, this could change.

9. Metformin is available as a lower-cost generic, while Mounjaro is a brand-name medication only

When it comes to treating Type 2 diabetes, cost is often a focus. Costs quickly add up, between medications, supplies for checking blood glucose, appointments, and more. So it’s not surprising that people want to get the best price on their prescriptions whenever they can.

One of the best ways to save on your prescriptions is to fill a generic version of a medication, when one is available. Metformin has been on the market for a while. And most dosage forms have a generic version.

GoodRx can help you save on metformin. The price of immediate-release metformin may be as low as $6.99 at certain pharmacies. And the price of extended-release metformin may be as low as $17.04.

Mounjaro is available only as a brand-name medication right now. Filling your prescription through your insurance, if applicable, is the best way to save on the medication. Manufacturer copay cards can also help lower costs. If you’re eligible, you could pay as little as $25 for Mounjaro with a copay savings card.

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Written by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

Reviewed by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Farah Naz Khan, MD

Farah Naz Khan, MD, is a board-certified physician at the UW Medicine Diabetes Institute and a clinical assistant professor of metabolism, endocrinology, and nutrition at the University of Washington.

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