If you have diabetes, your doctor might suggest Lantus (insulin glargine) as a treatment option for you.

Lantus is a prescription medication that’s used to improve blood sugar levels in:

  • adults with type 1 or type 2 diabetes
  • children ages 6 years and older with type 1 diabetes

Lantus comes as a solution that’s given as an injection under your skin once per day. Your doctor will show you how to use Lantus so you can give yourself injections at home.

If this medication works for you, your doctor will likely recommend that you take it long term for your diabetes. For more information about Lantus, see this in-depth article.

Like other drugs, Lantus can cause mild or serious side effects (also called adverse effects). Keep reading to learn more.

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:

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

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.

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.

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.

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

In studies, children using Lantus experienced similar side effects as adults using the medication. But low blood sugar was more common in children than in adults using Lantus. If your child is using 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 pain medications such as Tylenol (acetaminophen) or Advil (ibuprofen).

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 decrease this side effect, such as over-the-counter 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 using 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 over-the-counter pain relievers. They can also give you tips on injecting Lantus properly. This could help lower your risk of injection site reactions.

Allergic reaction

Like most drugs, Lantus can cause an allergic reaction in some people.

Symptoms can be mild or serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

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 an over-the-counter oral antihistamine, such as Benadryl (diphenhydramine), or a topical product, such as hydrocortisone cream, to manage your symptoms.

If your doctor confirms you had a mild allergic reaction to Lantus, they’ll decide whether you should continue using it.

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 had a serious allergic reaction to Lantus, they may have you switch to a different treatment.

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, using 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)?

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 may not be right for you if you have certain medical conditions or other factors that affect your health. Talk with your doctor about your health history before you take Lantus. The list below includes factors to consider.

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 using 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 using Lantus.

Alcohol use 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.

Pregnancy and breastfeeding while using Lantus

It’s not known if 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 recommends that females* with gestational diabetes (diabetes that develops during pregnancy) use insulin such as Lantus to help lower their blood sugar levels.

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.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Although you may experience side effects during your Lantus treatment, most side effects are mild. Before using Lantus, you should discuss your risk of side effects with your doctor. They can help you determine if 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?

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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.