Lantus (insulin glargine) is a prescription brand-name medication. It’s approved by the Food and Drug Administration (FDA) to improve blood sugar levels in:

Lantus is taken by subcutaneous injection. It’s typically used as a long-term treatment to help manage blood sugar levels.

Here are some fast facts about Lantus:

Like other drugs, Lantus can cause side effects (also called adverse effects or reactions). Read on to learn about potential common, mild, and serious side effects. For a general overview of Lantus, including details about its uses, see this article.

Lantus can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took Lantus in clinical trials:

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

Mild side effects can occur with Lantus use. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to Lantus’s prescribing information.

Mild side effects that have been reported with Lantus include:

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you develop a side effect while taking Lantus and want to tell the FDA about it, visit MedWatch.

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

Lantus may cause serious side effects. The list below may not include all possible serious side effects of the drug. For more information, you can refer to the Lantus prescribing information.

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

Serious side effects that have been reported and their symptoms include:

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

Lantus is used in children ages 6 years and older with type 1 diabetes. The side effects of Lantus in this age group are similar to the side effects in adults taking the drug. However, children are more likely than adults to have hypoglycemia (low blood sugar) with Lantus. And hypoglycemia is more likely to be severe in children.

If your child is prescribed Lantus, their doctor will likely recommend monitoring their blood sugar levels frequently. It’s important that you and your child know the symptoms of hypoglycemia and what to do if they occur.

For a list of symptoms to watch for and more information on hypoglycemia, see “Side effect specifics” below.

Lantus may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

I’m using the SoloStar pen for Lantus injections. What side effects can I expect?

There aren’t any known differences in side effects between Lantus vials and Lantus SoloStar pens.

However, most people find that the Solostar pen is easier and less painful to self-inject than the Lantus vial with the syringe and needle. For more information on side effects, see the “Mild side effects of Lantus” or “Serious side effects of Lantus” sections above.

Lantus is a solution given as a subcutaneous injection. This is done either with a vial and syringe or a prefilled SoloStar pen.

With Lantus vials, you’ll use a syringe and needle to withdraw your dose from the vial and inject it. With Lantus Solostar pens, you’ll first select your dose on the pen. Then you’ll attach a needle to the pen to inject your dose.

Does Lantus cause cancer as a side effect?

No, Lantus is not known to cause cancer. In clinical trials, the incidence of cancer was similar between treatment groups. And it hasn’t been reported since this medication has been available for use.

Certain drugs for type 2 diabetes called thiazolidinediones (TZDs) have been linked to bladder cancer in some people. TZDs include rosiglitazone (Avandia) and pioglitazone (Actos). However, it’s not known for certain if these drugs increase the risk of bladder cancer.

Lantus is not related to these drugs. Lantus is a type of insulin. And no types of insulin are known to cause cancer.

If you’re concerned about the risk of cancer with your diabetes medications, talk with your doctor.

I’m taking Lantus with Humalog. What side effects can I expect?

Lantus and Humalog are different types of insulin that are commonly prescribed together. Lantus is a long-acting insulin that’s taken once a day to help improve blood sugar levels over 24 hours. Humalog is a rapid-acting insulin that’s taken at mealtimes to manage increases in blood sugar after eating.

Both these types of insulin can cause similar side effects. When you use them together, you may have a higher risk of certain side effects, especially hypoglycemia (low blood sugar).

Be sure to talk with your doctor about how to avoid hypoglycemia with insulin treatment and what to do if you experience hypoglycemia. You can also read more about this side effect in “Side effect specifics” below.

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

Weight gain

Weight gain may occur after starting Lantus treatment. Weight gain is a common side effect of all types of insulin. And Lantus is a type of insulin.

Insulin can cause weight gain because it helps your body move sugar out of your blood and into your cells. Some of this sugar gets stored as fat, which can lead to weight gain.

What you can do

If you’re concerned about weight gain with Lantus, talk with your doctor about ways to maintain a weight that’s healthy for you. Your doctor, as well as your pharmacist, nutritionist, and other members of your diabetes care team, can give you advice on eating moderately and exercising regularly.

Note: If you take Lantus with a type of diabetes drug called a thiazolidinedione (TZD) and suddenly gain a lot of weight, talk with your doctor right away. Sudden weight gain could be a symptom of heart failure, which can be a problem with this combination of drugs. Examples of TZDs include rosiglitazone (Avandia) and pioglitazone (Actos).

Joint pain

Some people may have joint pain while taking Lantus. In clinical trials, this side effect was commonly reported in people with type 2 diabetes. However, it wasn’t reported in people with type 1 diabetes.

What you can do

If you have joint pain during Lantus treatment, it might help to rest the affected joint. However, if the pain is bothersome, ask your doctor or pharmacist if they can recommend a medication. They may recommend taking an over-the-counter (OTC) pain reliever, such as acetaminophen (Tylenol) or ibuprofen (Advil).

If you have joint pain that causes concern or affects your daily activities, talk with your doctor.

Diarrhea

It’s possible to have diarrhea while taking Lantus. In clinical trials, this side effect was common in people with type 2 diabetes. However, it wasn’t reported in people with type 1 diabetes.

What you can do

If you have diarrhea during Lantus treatment, be sure to drink plenty of fluids to avoid dehydration. If recommended by your doctor, diarrhea can also be treated with an OTC medication called loperamide (Imodium). You can also ask your doctor or pharmacist to recommend another suitable medication.

If you have diarrhea that’s bothersome or occurs often, talk with your doctor. They may recommend switching to a different medication for your diabetes.

Injection site reactions

Injection site reactions may occur with Lantus. Injections site reactions are commonly reported with all types of insulin, including Lantus. They can affect people with type 1 and type 2 diabetes.

These reactions may cause the following symptoms at your injection site:

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

Injection site reactions are typically mild and get better in a few days.

What you can do

To help avoid injection site reactions, inject each dose into a slightly different site in the area you use. Rotating your injections sites in this way can also help reduce the risk of lipodystrophy, which is another side effect of Lantus. (With lipodystrophy, you have skin thickening, lumps, dents, or pits at your injection site due to fatty tissue changes under the skin.) Do not choose an area of the skin that is bruised or injured.

You shouldn’t rub the injection site after an injection. This could irritate the area.

If you have an injection site reaction that’s particularly bothersome, you can try applying a cold pack. This can help relieve your symptoms. You can also ask your doctor or pharmacist to recommend a medication that is right for you. They may recommend an OTC pain reliever, such as acetaminophen (Tylenol) or ibuprofen (Advil).

If you have a reaction that’s severe or lasts longer than a few days, contact your doctor. You should also tell your doctor if you frequently have injection site reactions. They can check your injection technique and give you tips on how to inject Lantus correctly. This may reduce your risk of having a reaction. For more information on how to inject Lantus safely and correctly, you can also check out this article.

Hypoglycemia

As with all types of insulin, hypoglycemia (low blood sugar) is the most common side effect of Lantus. (Lantus is a type of insulin.)

Hypoglycemia typically causes mild symptoms at first. However, this side effect can quickly become serious and life threatening if it’s not treated.

Symptoms of mild hypoglycemia can include:

Symptoms of more severe hypoglycemia can include:

Severe hypoglycemia can lead to coma and even death.

Your risk of hypoglycemia can increase if you take too much Lantus or inject the drug in a different area of your body where injections aren’t recommended. This risk can also increase if you eat less than usual, skip a meal, or drink large amounts of alcohol. Doing more physical activity than usual may also increase this risk.

Other medications can also increase your risk of hypoglycemia if taken with Lantus. These include other types of insulin, or sulfonylureas such as glipizide (Glucotrol). Changes in your insulin treatment plan may affect this risk too.

What you can do

To help avoid hypoglycemia with Lantus, it’s important to carefully follow your doctor’s instructions for managing your diabetes. Talk with your doctor about how often and when you should check your blood sugar. Your doctor will also discuss how your dosage may need to be adjusted depending on what you eat and your activity levels. And if you use more than one type of insulin, be sure to check that you’re taking the correct one each time you take a dose.

If you have symptoms of hypoglycemia, you should eat or drink something containing sugar right away. This should be something that can be quickly absorbed by your body. Examples include:

  • glucose tablets
  • jelly beans
  • hard candy
  • sugary drinks (not diet or sugar-free drinks)
  • a tablespoon of honey or sugar

If you have symptoms of severe hypoglycemia, you should immediately call 911 or your local emergency number. If your symptoms include trouble swallowing or unconsciousness, it’s important that you don’t take, and that no one gives you, anything by mouth, such as sugar. This could cause you to choke. Instead, you’ll take glucagon as soon as possible if your doctor has prescribed this as part of your diabetes treatment plan.

If you often have episodes of hypoglycemia, contact your doctor. You should also contact your doctor if you have hypoglycemia according to your blood sugar test results, but don’t have noticeable symptoms. They can recommend how often you should check your blood sugar. They may also review your other diabetes medications or their dosages.

Allergic reaction

As with most drugs, Lantus can cause an allergic reaction in some people. Allergic reactions, including anaphylaxis, can be life threatening.

Symptoms can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • swelling under your skin, typically in your lips, eyelids, feet, or hands
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should keep taking Lantus. However, if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Be sure to talk with your doctor about your health history before you take Lantus. This drug may not be the right treatment for you if you have certain medical conditions or other factors that affect your health. The conditions and factors to consider include:

Hypoglycemia. Do not take Lantus if you’re having an episode of hypoglycemia (low blood sugar).* Lantus lowers your blood sugar and will worsen hypoglycemia. This could be fatal.

Allergic reaction. If you’ve had an allergic reaction* to Lantus or any of its ingredients, your doctor will likely not prescribe the drug. Ask your doctor what other medications may be better options for you.

Kidney or liver problems. If you have kidney or liver problems, you may have a higher risk of hypoglycemia with Lantus. Talk with your doctor about whether Lantus is right for you.

Hypokalemia. If you have hypokalemia, taking Lantus could make this worse. Other medications may also cause or increase your risk of hypokalemia. Make sure to tell your doctor about all of the drugs you take. Depending on your medications, your doctor may monitor your blood potassium level during treatment.

Heart failure or other heart problems. If you have heart failure, it may get worse while you take thiazolidinedione with Lantus. Talk with your doctor about whether these medications are right for you.

Pregnant or breastfeeding. It is not known if Lantus may harm your unborn baby or breastfeeding baby. Tell your doctor if you are pregnant, planning to become pregnant, or are breastfeeding to better inform your treatment plan.

*For more information about these side effects, see “Side effect specifics” above.

Alcohol and Lantus

Drinking alcohol can cause hypoglycemia. This can happen up to several hours after you stop drinking alcohol. Lantus can also cause hypoglycemia. So drinking alcohol with Lantus could increase your risk of hypoglycemia, especially severe hypoglycemia. Alcohol can also worsen this side effect. For more details about hypoglycemia and symptoms to watch for, see “Side effect specifics” above.

If you drink alcohol, talk with your doctor about how much, if any, you can safely drink while taking Lantus. They may recommend that you check your blood sugar more often than usual while you’re drinking alcohol.

Pregnancy and breastfeeding while taking Lantus

It’s not known for sure if Lantus is safe to take during pregnancy. So far, clinical trials haven’t linked Lantus with any risk of problems with fetal development (commonly called birth defects).

With diabetes, it’s important to maintain healthy blood sugar levels during pregnancy. For this reason, the American Diabetes Association recommends treatment with insulin, such as Lantus.

Lantus may pass into breast milk if taken while breastfeeding. However, it’s unlikely that Lantus will cause side effects in a child who’s breastfed. Insulin is generally considered safe to use while breastfeeding.

If you’re pregnant or breastfeeding, or are planning either, talk with your doctor before starting Lantus. If you do take Lantus while pregnant or breastfeeding, it’s likely that your doctor will adjust your dosage.

Lantus has some common side effects, but most are mild and easily managed. However, some serious side effects are also possible.

Talk with your doctor about your risk of side effects with Lantus, including your risk of hypoglycemia (low blood sugar). They can help you decide if this medication is a good option for you. (See “Side effect specifics” above for more details about hypoglycemia and other possible side effects.)

If you’d like to learn more about Lantus, talk with your doctor or pharmacist. They can help answer any questions you have about side effects of taking the drug.

Besides talking with your doctor, you can do some research on your own. These articles might help:

Disclaimer: Medical News Today 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.