9 Janumet Side Effects You Should Know About

Metformin is the most frequently prescribed diabetes medication. But if you’re taking it and need more help lowering your blood glucose (sugar), Januvia (sitagliptin) can be a potential addition. To make your life easier, the two medications also come together in a single pill called Janumet. An extended-release version, called Janumet XR, is also available.

The same side effects are possible with Janumet as could occur if you were taking metformin and Januvia separately. Diarrhea, headache, and nausea are a few examples. In rare cases, pancreatitis has been reported. Here is a closer look at potential Janumet side effects. 

Janumet side effects at a glance

Many Janumet side effects are mild and tend to improve over time. While rare, more serious side effects are also possible.

Common Janumet and Janumet XR side effects include:

• Diarrhea

• Upper respiratory tract infections (URTIs)

• Headache

• Nausea and vomiting

• Abdominal pain

Less common and potentially serious Janumet and Janumet XR side effects include:

• Hypoglycemia (low blood glucose)

• Pancreatitis

• Lactic acidosis

• Heart failure

• Kidney damage

• Vitamin B12 deficiency

• Allergic reactions

• Severe joint pain

• Bullous pemphigoid (a rare skin condition)

Whether you’re experiencing Janumet side effects or just curious about what to expect, here is what you should know about nine of these side effects.

1. Diarrhea

Diarrhea is one of the most common Janumet side effects. This is mostly due to the metformin component, which is well-known for causing diarrhea when you start taking it. Fortunately, this side effect gets better after a few weeks for most people.

Even though it’s short-lived, diarrhea from Janumet can be tough to tolerate. There are a few things you can do to manage it. For example, Janumet should be taken with meals to lessen gut-related side effects. You can also try eating a bland diet for a short period of time.

If you’re still experiencing diarrhea after a few weeks, or if it’s affecting your daily functioning, talk to your healthcare provider. They may recommend additional lifestyle changes, an over-the-counter (OTC) antidiarrheal, or a dose change.

2. Nausea and vomiting

The metformin component in Janumet can also cause nausea and vomiting. You may need to give your body a few weeks for these side effects to subside.

In addition to taking your dose with food, a few other things you can do to manage nausea and vomiting include:

• Avoid spicy or greasy foods

• Eat smaller and more frequent meals

• Try ginger or peppermint in teas, capsules, or oils

• Use an acupressure wristband

• Talk to your provider or pharmacist about OTC anti-nausea medications

If you experience these gut-related side effects, drink plenty of water to prevent dehydration. Dehydration can increase your risk of more serious Janumet side effects, such as lactic acidosis. Let your healthcare provider know if your nausea and vomiting aren’t letting up or get worse.

3. Upper respiratory tract infections

Some people taking Janumet report upper respiratory tract infections (URTIs), a common Januvia side effect. But keep in mind that diabetes itself can increase your risk of infections in general.

Common URTI symptoms include a cough, stuffy or runny nose, and sore throat. Although these symptoms can be bothersome, URTIs will usually resolve on their own. In the meantime, your pharmacist can recommend OTC products to manage your symptoms.

If you’re not starting to feel better after 10 days, or if your symptoms are severe or getting worse, contact your healthcare provider. It’s possible that your infection is caused by bacteria and you need an antibiotic.

4. Headache

Headache is another common Janumet side effect, especially as you’re starting treatment. Over time, headaches may subside as your body gets used to Janumet. But headaches can also be a sign that your blood glucose is too low or too high.

To manage this side effect, make sure to get enough sleep and drink plenty of fluids. It’s also a good idea to avoid alcohol or limit your intake, since it can worsen headache symptoms. If your headaches aren’t getting better, talk to your pharmacist about an OTC pain reliever such as acetaminophen (Tylenol).

If you’re experiencing headaches with other symptoms, such as blurry vision or weakness, check your blood glucose. Depending on your reading, follow the instructions given to you by your healthcare team. If your headaches are persistent or severe, contact your provider.

5. Hypoglycemia

When taken on its own, Janumet has a low risk of hypoglycemia — when your blood glucose is below 70 mg/dL. But if you take it with insulin or sulfonylureas, your hypoglycemia risk goes up.

Common hypoglycemia symptoms include sweating, shaking, and hunger. You may also feel like your heart is beating faster than usual. If left untreated, hypoglycemia can be dangerous. It’s important to treat it quickly by following the steps given to you by your healthcare team.

Make sure to eat regular meals and snacks while taking Janumet. Monitor your blood glucose as recommended by your provider, since you may not always realize your levels are too low. It’s also a good idea to check your blood glucose before physical activity.

Let your healthcare provider know if  you experience frequent hypoglycemia episodes with Janumet. They may need to lower your dose or change your diabetes regimen.

6. Vitamin B12 deficiency

The metformin in Janumet has been linked to lower B12 levels, especially if you’ve taken higher doses for a long time. This doesn’t cause an issue for everyone, but some people may develop a B12 deficiency. This can result in anemia (low red blood cells) or nerve damage.

As part of your routine follow-ups, your healthcare provider may monitor your B12 levels while you’re taking Janumet. Your diet is an important source of B12. But if your levels are getting too low, your provider may suggest adding a B12 supplement.

7. Lactic acidosis

Because it contains metformin, Janumet has a boxed warning (the FDA’s strictest warning) for risk of developing lactic acidosis. Lactic acidosis occurs when there’s too much lactic acid in your blood. If left untreated, it can be life-threatening.

Lactic acidosis from Janumet is rare. But if you have kidney disease, your body may not be able to clear metformin as well, increasing your risk of lactic acidosis. Certain people with kidney disease may still be able to take Janumet. But this will depend on how well your kidneys work. Your provider will monitor your kidney function during treatment.

Other risk factors for lactic acidosis can include:

• Age (those 65 or older have higher risk)

• Dehydration

• Medication usage (some interact with Janumet)

• Excessive alcohol intake

• Liver disease

Confusion, fast heartbeat, and rapid breathing can be symptoms of lactic acidosis. If these develop, get medical help right away.

8. Pancreatitis

While rare, pancreatitis (inflammation of the pancreas) is another serious potential Janumet side effect. 

Pancreatitis symptoms can include yellowing of the skin and eyes (jaundice), severe abdominal pain, and nausea and vomiting. Get immediate medical attention if these symptoms develop, since untreated pancreatitis can be life-threatening.

9. Kidney problems

The Januvia component in Janumet has been linked to kidney problems. This side effect is rare and usually reverses after you stop taking Janumet. Janumet is more likely to affect your kidneys if you already have kidney disease, since your body isn’t able to process the medication as well.

During treatment, your healthcare provider will monitor your kidney health to ensure that Janumet is safe for you to take. If your kidney function declines, they may lower your dose or have you stop taking Janumet.

Let your healthcare provider know if you develop symptoms of new or worsening kidney problems, such as changes in your urination frequency, muscle cramps, or swelling in your legs.

When should you contact your healthcare provider about Janumet side effects?

If you have questions about Janumet side effects, your healthcare provider or pharmacist can be helpful resources. If any side effects concern you, aren’t going away, or worsen, don’t hesitate to reach out.

Several Janumet side effects, such as diarrhea and nausea, are usually temporary. A few tweaks to your food choices and eating schedule may clear them up. If needed, OTC products may also provide relief.

Some Janumet side effects are more serious and require immediate medical attention. Jaundice, rapid breathing, and severe abdominal pain are a few examples. If any symptoms feel severe or life-threatening, go to the nearest emergency room or call emergency responders.

Why trust our experts?

Written by:

Sandy P. Bonfin, PharmD, BCPS

Sandy Bonfin has 9 years of experience as a pharmacist and has been working as a clinical pharmacist in a hospital in Florida for the past 7 years after a short stint as a mail-order retail pharmacist. Sandy has worked in pediatric medicine, emergency medicine, internal medicine, and intensive care.

Edited 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:

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.

Our editorial standards

Meet our experts