8 Lantus (Insulin Glargine) Side Effects You Should Know About

If you have Type 1 or Type 2 diabetes, your healthcare team may prescribe insulin to help you manage your blood glucose (sugar) levels. There are several different types of insulin. Some work within minutes and are injected right before or after a meal. Others take longer to work, but last longer in the body.

Lantus (insulin glargine) is a long-acting, injectable insulin. It takes about 1.5 to 2 hours to start working, with Lantus effects lasting for about 24 hours. The FDA approved it in 2000. It’s available as a reference (brand-name) biologic. It also has two interchangeable biosimilars available: Semglee (insulin glargine-yfgn) and Rezvoglar (insulin glargine-aglr).

Lantus and other forms of insulin glargine are safe and work well for managing blood sugar levels. But like all medications, they can cause side effects. For instance, Lantus can cause headaches and weight gain. But which side effects are serious? And which ones can be managed at home?

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Lantus (insulin glargine) side effects at a glance

Most of Lantus’ side effects are mild in nature. And they can be managed at home with lifestyle changes or common over-the-counter (OTC) medications. But more serious side effects are possible. So it’s good to know what to expect if you’re just getting started with this insulin.

Common or mild Lantus side effects include:

• Upper respiratory tract infections

• Weight gain

• Swelling, especially of the hands or feet

• Injection site reactions

• Lipodystrophy (changes to how your body stores fat) around where you inject Lantus

• Temporary blood pressure increase

• Joint or back pain

• Cough

• Urinary tract infections (UTIs)

• Diarrhea

More serious Lantus side effects include:

• Hypoglycemia (low blood glucose)

• Low potassium levels

• Allergic reactions

• Mood changes

• Accidental injury

This list doesn’t include all possible Lantus side effects. Make sure to tell your prescriber about any side effects that are bothersome or persistent, even if they’re not listed here.

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Below, we detail eight Lantus side effects and how you can manage them if they happen to you.

Good to know: Semglee and Rezvoglar are interchangeable with Lantus. So you can expect similar side effects for all three forms of insulin glargine.

1. Headaches

Headaches may happen after starting Lantus, especially if your blood sugar spikes and drops frequently. Both high and low blood sugar can cause headaches. These should go away as Lantus starts stabilizing your blood sugar levels.

In the meantime, there are things you can do to help with headaches:

• Make sure you’re drinking enough water.

• Take steps to optimize your sleep routine so you get enough rest at night.

• Try to exercise regularly if you can.

• Try activities that can help lower stress levels, such as mindfulness and deep breathing.

• Ask a healthcare professional if you can safely take OTC pain relievers, such as acetaminophen (Tylenol).

Headaches are a possible symptom of hypoglycemia, a more serious Lantus side effect. If you have a headache, it’s a good idea to check your blood sugar. Talk to your prescriber if your headaches are persistent or severe. This is not a typical Lantus side effect.

2. Weight gain

Weight gain is a common side effect for all insulins, including Lantus. One study found that people with Type 2 diabetes gained an average of 4 lbs after using Lantus for 1 year. But everyone’s experience is different. So you may gain more or less than this.

A diabetes-friendly diet and exercise routine may help keep your weight and blood sugar in ranges that are healthy for you. These lifestyle changes can also help lower the risk of long-term complications of diabetes, such as kidney damage or heart disease.

If you start to gain weight with Lantus, talk to your healthcare team. They may suggest changes in your diabetes care plan. This might include adding medication to help you lose weight.

3. Injection site reactions

Because Lantus is injected under the skin, it can cause injection site reactions. This is when you experience redness, swelling, or pain where you inject a medication. Sometimes you may experience bleeding or a mild skin rash, as well.

To lower your risk of injection site reactions, change the area where you inject Lantus every time. You can rotate between your stomach, thigh, and the back of your upper arms. And within each of these sites, you can inject in different areas. For example, if you’re injecting Lantus into your stomach area, use a different spot on the stomach for each injection.

Most injection site reactions improve on their own within 1 to 2 days. If you experience redness or pain after injecting Lantus, a cold compress might help. You can also ask your healthcare team if you can take an OTC pain reliever, such as acetaminophen.

For any reaction that seems severe or lasts longer than a few days, talk with your prescriber. They may have recommendations to improve your injection technique, which can be a common cause of injection site reactions.

4. Upper respiratory tract infections

In clinical trials, upper respiratory tract infections (URTIs) were commonly reported in people using Lantus. The common cold is an example of a URTI. But this may be due to diabetes itself rather than Lantus. Having diabetes can raise the risk of getting infections.

Most URTIs will resolve on their own within 2 weeks. They’re often caused by viruses, so antibiotics aren’t needed. If you’re uncomfortable, talk to a healthcare professional about OTC products that can help relieve symptoms, such as congestion, pain, or cough. They can suggest a diabetes-safe option. Some OTC medications can raise your blood sugar, especially if they contain sugar as an inactive ingredient.

Sometimes having a URTI can cause you to lose your appetite, which can lower your blood sugar levels. If this occurs, talk with your care team right away. They can adjust your Lantus dosage to make sure that your blood sugar doesn’t drop too low.

5. ​​Lipodystrophy

Lantus can cause lipodystrophy. This is a problem with the way your body stores fat. Lipodystrophy causes fat loss in certain areas and fat accumulation in others.

Signs of lipodystrophy include noticeable changes in the way fat is distributed throughout your body. These changes occur specifically in the areas where insulin is injected. Areas with reduced fat can look like pits (indentations) in the skin. Areas with more fat can appear as thickened skin.

Lipodystrophy with Lantus is often caused by incorrect injection technique. This includes forgetting to rotate injection sites or reusing needles. To lower your chances of lipodystrophy, follow the steps for injecting Lantus properly. Make sure to rotate injection sites each time and never reuse needles or syringes.

6. Low potassium levels

Lantus can cause hypokalemia (low potassium levels). Your risk may be higher if you also take other medications that lower potassium, such as certain diuretics (water pills).

Most people don’t experience symptoms if their potassium levels are low. Possible symptoms include muscle weakness, dizziness, and constipation. But severely low levels can cause abnormal heart rhythms (arrhythmias) or cause your heart to stop (cardiac arrest).

Your healthcare team will likely order potassium blood tests from time to time while you use Lantus. If your potassium is low, they may prescribe a potassium supplement, such as potassium chloride (Klor-Con).

7. Low blood glucose (sugar)

Lantus works by lowering your blood glucose in your body. But in some cases, it can lower your blood sugar too much (hypoglycemia).

Your risk of this is higher if you also take other diabetes medications. This is especially the case if these medications directly affect insulin release in your body. Examples include sulfonylureas, such as glipizide (Glucotrol XL), and glitazones, such as pioglitazone (Actos). If you start another diabetes medication, your prescriber will likely lower your Lantus dose to help prevent low blood sugar.

It’s important to check your blood sugar regularly if you use Lantus. If you use a continuous glucose monitor (CGM), always verify potential low blood sugar readings with a glucometer. CGMs have a slight lag-time, so you may feel hypoglycemia symptoms before the device shows low blood sugar readings.

You should also know the symptoms of hypoglycemia. These include:

• Fast heart rate

• Dizziness

• Sweating

• Tiredness

• Shakiness

• Weakness

• Anxiety

• Hunger

Often, hypoglycemia can be treated with a fast-acting sugar source, such as 4 glucose tablets, 1 tube of glucose gel, or a half cup of fruit juice or regular soda. If hypoglycemia isn’t treated, it can lead to unconsciousness, seizures, and even death. It’s a good idea to always carry a fast-acting glucose source with you in case you need it.

8. Allergic reactions

Life-threatening allergic reactions, including anaphylaxis, to Lantus are rare, but they can happen. Possible symptoms of a severe allergic reaction are a rash, abdominal pain, and a fast heartbeat. Call 911 if you experience trouble breathing or swelling of the face, tongue, or throat.

If you’re allergic to Lantus, your prescriber may suggest that you switch insulin products. An allergy to Lantus doesn’t mean you’ll have a reaction to other insulins. If you have Type 2 diabetes, they may also recommend switching to a different type of diabetes medication.

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Written by:

Makaela Premont, PharmD

Makaela Premont, PharmD, is a pharmacist and the founder of uniquelymickie.com, a website dedicated to helping pharmacy students and pharmacists create a life that they enjoy. She received her Doctorate of Pharmacy from the University of South Carolina and is a licensed pharmacist in North Carolina.

Written by:

Daphne Berryhill, RPh

Daphne Berryhill, RPh, has two decades of experience as a clinical pharmacist. She spent most of her career in the Chicago area practicing in-home infusion.

Reviewed 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.

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