Metformin vs. Ozempic: Side Effects, Cost, and Results

Written by Sharon Liao
Medically Reviewed by Michael Dansinger, MD on August 27, 2025
7 min read

Metformin (Fortamet, Glumetza) and semaglutide (Ozempic, Rybelsus) are medicines that treat type 2 diabetes. They both lower blood sugar, but they work differently. Metformin is a pill or liquid that’s taken once or twice a day. Ozempic is a once-a-week shot.

The two medicines act differently to manage blood sugar. Metformin lowers the amount of glucose that your liver makes and boosts insulin sensitivity. Ozempic mimics the effects of a gut hormone called GLP-1. It triggers your pancreas to release more insulin and slows down how quickly food leaves your body. It also sends signals to your brain that you’re full, which can lead to weight loss.

What is metformin?

Metformin has been around longer. Although it was approved in 1994, it’s still a first-choice treatment for diabetes, says Michelle Ponder, MD, an endocrinologist and assistant professor of medicine at Duke University. "It's usually prescribed to people who are newly diagnosed with diabetes or have mild to moderate cases," she says. It’s not FDA-approved for obesity. 

What is Ozempic?

Ozempic, which is the brand name of the injectable form of semaglutide, is a newer and stronger drug. It became available in 2017 and belongs to a class of drugs called GLP-1 agonists. It's not prescribed as often as metformin, but it's a good fit for certain people. If you have diabetes and heart disease, semaglutide lowers the risk of heart attacks and strokes. It also protects the kidneys.

People with overweight or obesity may benefit more from Ozempic. "Weight loss is a side effect for both medicines, but Ozempic has a bigger effect," Ponder says. Other GLP-1 agonist drugs for diabetes, including Mounjaro (tirzepatide), have similar benefits. There are also higher-dose versions of these medicines, such as Wegovy (semaglutide) and Zepbound (tirzepatide), that have been recently approved for weight loss alone.

If you have diabetes, talk to your doctor about which medicine is right for you. Although both metformin and Ozempic can lower your blood sugar, there are some important differences between the two medicines. Price is often a factor: Because metformin is available as a generic drug, it’s widely available and much more affordable.

One of the biggest differences between the two medications is how they're taken, says Deborah Horn, DO, director of obesity medicine at UTHealth Houston. Metformin is a pill or liquid that you swallow daily. You usually start with 500 milligrams at breakfast and dinner, or 850 milligrams at breakfast. Your doctor may increase your dose if your blood sugar isn’t controlled. There's also an extended-release formula that breaks down more slowly. You take it once a day with your evening meal.

Ozempic is an injection that you give yourself once a week. It comes in a disposable push-button pen that’s easy to use. Because it takes time to adjust to the medicine, the dosage increases over months, says Ponder. You’ll begin with 0.25 milligrams for four weeks, and then you take 0.5 milligrams a week for at least another four weeks. You can have up to 2 milligrams each week.

How these medicines are taken may affect your decision. If you’re afraid of needles, metformin is an easier option. Ozempic may be a better choice if you can't remember a daily pill.

Metformin and Ozempic have similar side effects, including diarrhea and an upset stomach. "The side effects for metformin are usually milder, and they resolve with time or by eating some food," Horn says. "But Ozempic’s are a little tougher and trickier to treat. It’s not as well tolerated."

Metformin has a longer track record than Ozempic. It’s been widely used for decades, so its effects are well known. Because Ozempic hit the market in 2017, there’s not as much long-term data about its side effects.

What are the side effects of metformin?

The most common side effects of metformin include:

  • Stomach pain or upset
  • Diarrhea
  • Nausea
  • Bloating and gas
  • Heartburn and indigestion
  • Headache
  • Metallic taste

What are the side effects of Ozempic?

The most common side effects of Ozempic include:

  • Nausea
  • Diarrhea
  • Constipation
  • Throwing up
  • Bloating and gas
  • Heartburn and indigestion

Although metformin and Ozempic aren't prescribed for weight loss, both medicines can cause you to lose weight. Ozempic is the more powerful of the two treatments, Ponder says. Research shows that people with type 2 diabetes and obesity lost an average of 5% to 6% of their body weight after taking Ozempic for a year. That's compared to a 2% loss for those using metformin after two years. 

In recent years, stronger versions of these GLP-1s were approved to help people with overweight and obesity. These include semaglutide, the same medicine in Ozempic, which is called Wegovy. Others are liraglutide (Saxenda) and tirzepatide (Zepbound). These medicines can lead to even more weight loss – about a 10% to 20% drop in body weight after a year. 

Both metformin and Ozempic can help treat the symptoms of polycystic ovary syndrome (PCOS). PCOS often causes insulin resistance (when your body doesn’t respond properly to this hormone) and weight gain. Metformin can improve insulin sensitivity. It’s a good option for people with PCOS who don’t need to lose weight, says Ponder. Ozempic can lower blood sugar and lead to significant weight loss. 

Doctors prescribe metformin to lower blood sugar levels in people with prediabetes. The medicine can lower your risk of developing type 2 diabetes when diet and lifestyle changes aren’t enough, says Rachel Pessah-Pollack, MD, an endocrinologist and clinical professor of medicine at NYU Langone Health.

Ozempic isn't approved to treat prediabetes. As a result, your health insurance probably won't cover it. But Ozempic can lower blood sugar and cause weight loss in people with prediabetes. 

Metformin is a generic drug, so it costs much less than Ozempic. Metformin is more likely to be covered by health insurance, says Ponder. 

With insurance

It depends on your insurance coverage, but metformin tends to cost around $4 a month, says Horn. If you have Medicare, it may cover much or all of the cost. Ozempic's monthly cost can range from $25 to $200. 

Without insurance

Even without insurance, metformin ranges from $4 to $15, says Pessah-Pollack. Ozempic prices are hundreds of times more. A month's supply can cost $1,000 to $1,400.

Because the drugs work in different ways, Ozempic won't replace metformin entirely. But you can switch from one medicine to the other, says Pessah-Pollack. Your diabetes may be under control with metformin, but your doctor could suggest Ozempic if you have heart disease or need to lose weight. If you have severe diabetes, you may need to take metformin and Ozempic at the same time.

On the flip side, you may need to switch to metformin if you can't tolerate Ozempic's side effects or if the price is too high.

Metformin and Ozempic are both prescribed to manage blood sugar in people with type 2 diabetes, but there are some important differences between the two. Metformin is usually a first-line medication because the pill is easy to take and it's affordable. Ozempic is a stronger drug. It causes more weight loss and can protect against heart and kidney disease complications. But it's also more expensive and can cause more side effects. Talk to your doctor about which medication is best for you.

Here are some commonly asked questions about the differences between metformin and Ozempic.

What are the long-term effects of Ozempic vs. metformin?

Doctors know more about metformin’s long-term effects. It's safe to use in the long run, and research shows taking it for more than six years may even help protect your mental sharpness. Metformin can lead to a vitamin B12 deficiency, so your doctor should test for that every year. Because Ozempic is a newer drug, scientists are still studying its long-term effects. In rare cases, GLP-1 agonists like Ozempic have been linked with eye problems, gallbladder and pancreas problems, blocked intestines, and stomach paralysis (a condition in which your stomach muscles don't contract as they should to help you digest food).

How do I know which weight loss drug is better for me?

Ozempic and metformin are prescribed to manage blood sugar in people with type 2 diabetes, although weight loss is a side effect. If you need to lose weight for your health, Ozempic is more effective. Metformin causes a moderate amount of weight loss over a longer period of time, says Horn. 

Can you switch between the two drugs?

You can switch between metformin and Ozempic, says Pessah-Pollack. You can also take both at the same time.