Lantus (insulin glargine) is a prescription drug that’s used to manage diabetes in adults and certain children. Lantus can cause side effects that range from mild to serious. Examples include diarrhea and joint pain.

Specifically, Lantus is used to manage blood sugar levels in:

Keep reading to learn about the common, mild, and serious side effects (also called adverse effects) that Lantus can cause. For a general overview of the drug, including details about its uses, see this article.

Some people may experience mild or serious side effects during their Lantus treatment. Examples of commonly reported side effects from Lantus include:

* To learn more about this side effect, see “Side effects explained” below.

Some people using Lantus may experience mild side effects. Examples of mild side effects that have been reported with Lantus include:

In most cases, these side effects should be temporary. And some may be easily managed, too. But if you have any symptoms that are ongoing or that bother you, talk with your doctor or pharmacist. You shouldn’t stop using Lantus unless your doctor recommends it.

Lantus may cause mild side effects other than the ones listed above. See the Lantus prescribing information for details.

* To learn more about this side effect, see “Side effects explained” below.

Using Lantus may cause serious side effects in some people. Serious side effects that have been reported with Lantus include:

If you develop serious side effects while using Lantus, call your doctor right away. If the side effects seem life threatening or if you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Lantus, visit MedWatch.

Allergic reaction

For some people, Lantus can cause an allergic reaction. This side effect was reported in the drug’s studies.

In general, symptoms of allergic reaction can be mild or serious. You can learn more about possible symptoms in this article.

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms and can determine whether you should keep taking Lantus.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to Lantus, they may have you switch to a different treatment.

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In studies, children receiving Lantus experienced similar side effects as adults undergoing treatment with the medication. But low blood sugar was more common in children than in adults. If your child is prescribed Lantus, their doctor may recommend more frequent blood sugar monitoring.

Learn more about some of the side effects Lantus may cause.

Weight gain

Some people may experience weight gain during their Lantus treatment. In studies, this was one of the most common side effects seen in people using Lantus.

Weight gain is common with many other types of insulin as well. This is due to the way that insulin works in your body to help you store blood sugar.

What might help

If you’re concerned about weight gain during your Lantus treatment, talk with your doctor. They may recommend changes to your diet or exercise routine to help you reach or maintain a moderate weight.

Joint pain

Joint pain is possible during Lantus treatment. This was one of the more common side effects reported in people using Lantus in studies.

In the studies, joint pain was reported only in adults using Lantus for type 2 diabetes. It was not reported in children or adults using the drug for type 1 diabetes.

What might help

If you experience joint pain during your Lantus treatment, talk with your doctor. They may be able to recommend ways to ease this side effect. This may include taking over-the-counter (OTC) pain medications such as acetaminophen (Tylenol) or ibuprofen (Advil).

Diarrhea

Some people may experience diarrhea while using Lantus. In studies, this was another common side effect reported by people using the drug.

In the studies, diarrhea was reported only by adults using Lantus to treat type 2 diabetes. It didn’t occur in adults or children using the drug for type 1 diabetes.

What might help

If you experience diarrhea during your Lantus treatment, especially if it’s frequent or bothersome to you, be sure to tell your doctor. They can recommend ways to manage this side effect, such as OTC diarrhea treatments.

Injection site reactions

You may experience injection site reactions in the area where you inject Lantus. In studies, injection site reactions were common in people receiving Lantus.

Some examples of injection site reactions include:

  • redness or discoloration
  • pain
  • skin rash
  • itching
  • swelling

What might help

If you have injection site reactions that are frequent, painful, or bothersome, tell your doctor. They can recommend ways to ease the pain from these reactions, such as taking OTC pain relievers. They can also give you tips on injecting Lantus properly. This could help lower your risk of injection site reactions.

Keeping track of side effects

During your Lantus treatment, consider keeping notes on any side effects you’re having. Then, you can share this information with your doctor. This is especially helpful to do when you first start taking new drugs or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of drug you were using when you had the side effect
  • how soon after starting that dose you had the side effect
  • what your symptoms were from the side effect
  • how it affected your daily activities
  • what other medications you were also taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help your doctor learn more about how Lantus affects you. And your doctor can use this information to adjust your treatment plan if needed.

Get answers to some frequently asked questions about Lantus’ side effects.

Could treatment with Lantus cause cancer?

No, receiving Lantus doesn’t raise your risk of cancer. A study looked at whether Lantus increased the risk of cancer or death from cancer compared with other diabetes treatments. The study showed that the risk of cancer or death from cancer was about equal among people using Lantus and people using other diabetes drugs.

This means that Lantus shouldn’t raise your risk of cancer. If you have other questions or concerns about Lantus and cancer, talk with your doctor or pharmacist.

Do the side effects of Lantus vary depending on its form (the prefilled pen or the vial used with needles)?

It’s unlikely. Lantus prefilled pens and Lantus vials both contain the same active drug, insulin glargine. This means that side effects should not vary between the two forms.

If you have other questions about the differences between Lantus prefilled pens and Lantus vials, talk with your doctor or pharmacist.

How long do Lantus side effects last?

It depends on which side effects you’re experiencing. For example, if you have injection site reactions such as pain or itching, you may experience this reaction with each injection. But symptoms of the reaction may be less severe or less frequent as you continue to use Lantus. Other side effects, such as joint pain or weight gain, may last longer.

If you’re experiencing side effects that are bothersome or that won’t go away, talk with your doctor. They may be able to recommend treatment for your side effects. Or they may have you stop using Lantus and switch to a different drug.

Lantus can sometimes cause harmful effects in people who have certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether Lantus is a good treatment option for you.

Talk with your doctor about your health history before you use Lantus. Be sure to tell them if any of the following factors apply to you:

Allergic reaction: If you’ve had an allergic reaction to Lantus or any of its ingredients, your doctor likely won’t prescribe Lantus. Ask your doctor what other medications are better options for you.

Low potassium levels: Lantus may cause you to develop low potassium levels. If you already have this condition, Lantus can make it even worse. If your potassium gets too low, it can be very serious or even life threatening. Before you start Lantus treatment, talk with your doctor if you have low potassium levels. They may recommend treating this condition before you start receiving Lantus.

Low blood sugar levels: Lantus works by improving your blood sugar levels. However, if your levels are already low, Lantus may reduce your blood sugar even more. This can be dangerous and even life threatening. If you have low blood sugar, your doctor will likely recommend treating this condition before you start receiving Lantus.

Alcohol and Lantus

Drinking alcohol is not recommended during your Lantus treatment. Both alcohol and Lantus can lower your blood sugar levels, so combining them can cause your blood sugar to get too low.

If you have questions about alcohol use with Lantus, talk with your doctor or pharmacist. For details about how Lantus interacts with other substances, including alcohol, see this article.

Pregnancy and breastfeeding while using Lantus

It’s not known whether Lantus may be safe to take during pregnancy. So far, studies have shown that Lantus does not cause an increased risk of problems with fetal development (commonly known as birth defects). But more studies are needed to determine the possible risk.

It’s important to note that untreated diabetes during pregnancy can cause harm to a fetus.

The American Diabetes Association (ADA) recommends that people with gestational diabetes use insulin, such as Lantus, to help lower their blood sugar. (Gestational diabetes is diabetes that develops during pregnancy.)

If you have preexisting diabetes and become pregnant, talk with your doctor. If you’re not already taking an insulin drug, they may prescribe one during your pregnancy.

At this time, it’s also unknown whether Lantus may be safe to use while breastfeeding.

If you’re pregnant or breastfeeding, or planning to become pregnant or to breastfeed, talk with your doctor before using Lantus.

Although you may experience side effects during your Lantus treatment, most side effects are mild. Before starting treatment with Lantus, you should discuss your risk of side effects with your doctor. They can help you determine whether Lantus may be a good treatment option for you.

Some questions you may want to ask your doctor include:

  • How should I treat side effects that I have from Lantus?
  • What other treatment options are available if I can’t tolerate the side effects of Lantus?
  • What should I do if I become pregnant while using Lantus?

Q:

If I have side effects from Lantus, can my dose be reduced?

Anonymous

A:

Yes, your Lantus dose may be adjusted if you’re experiencing side effects that continue to be bothersome. Most mild side effects typically go away after a few days. But if you have side effects that don’t go away, talk with your doctor. They can help determine whether your Lantus dose should be adjusted to help lower your risk of side effects. You should make changes to your dose only as recommended by your doctor.

The Healthline Pharmacist TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.
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Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.