Lantus Side Effects: What It Treats, How It Works, and What to Watch For

Lantus side effects most commonly include low blood sugar (hypoglycemia), reactions where the injection is given, weight gain and swelling. Lantus is a long-acting insulin used to help manage blood glucose in certain people with diabetes; it should be used exactly as prescribed, with attention to blood glucose monitoring and symptoms of low blood sugar.

Lantus at a Glance

Lantus is a prescription brand of insulin glargine, a long-acting insulin. It is designed to provide a relatively steady level of insulin over about 24 hours and is usually given once daily at the same time each day. It is used as part of an overall diabetes plan that may also include food choices, physical activity, blood glucose monitoring and other medicines.

Under the United States prescribing information, Lantus is used to improve blood glucose control in adults and children aged 6 years and older with type 1 diabetes, and in adults with type 2 diabetes. It is not intended for treatment of diabetic ketoacidosis, which requires urgent medical care and typically short-acting insulin. Approved uses may vary between countries, so patients should follow the information supplied with their own medicine and their clinician’s advice.

How Lantus Works and What It Treats

Insulin helps glucose move from the bloodstream into cells, where it can be used for energy or stored. In type 1 diabetes, the body produces little or no insulin. In type 2 diabetes, the body may not make enough insulin or may not respond to insulin effectively. Without sufficient insulin action, blood glucose can remain too high over time.

After injection under the skin, insulin glargine forms a small depot that releases insulin gradually. This makes it a basal, or background, insulin rather than an insulin intended to cover a meal immediately. People with type 1 diabetes generally need a separate rapid- or short-acting insulin for meals as well. A clinician determines whether Lantus is appropriate and how it fits into an individual’s diabetes treatment plan.

Common and Important Lantus Side Effects

The most common and clinically important side effect of Lantus is hypoglycemia, also called low blood sugar. It may occur when insulin needs are lower than expected, such as after eating less than usual, increasing physical activity, drinking alcohol, being unwell, or using certain other medicines. Possible symptoms include sweating, shakiness, hunger, headache, dizziness, fast heartbeat, irritability, confusion or difficulty concentrating. Symptoms vary, and some people may have reduced awareness of low blood sugar.

Other possible side effects include redness, pain, itching, swelling or rash at an injection site. Repeated injections into the same area can lead to lipodystrophy, meaning thickened, enlarged or sunken fatty tissue under the skin. This can affect how insulin is absorbed. Weight gain and swelling caused by fluid retention may also occur with insulin treatment. Rotating injection sites within the recommended body area can help reduce local skin changes.

Less commonly, insulin can cause allergic reactions. A severe, whole-body allergic reaction may include widespread rash or hives, swelling of the face or throat, trouble breathing, a fast pulse, marked sweating or light-headedness. This needs emergency medical attention. Low potassium levels can also occur with insulin and may be important for people taking medicines that affect potassium or those with certain heart conditions.

Who Should Use Caution and Key Interactions

Lantus should not be used during an episode of hypoglycemia. It is also contraindicated for people with a known hypersensitivity to insulin glargine or any ingredient in the product. People with kidney or liver problems, those who are older, and people whose eating patterns or activity levels change may need closer monitoring because their risk of hypoglycemia can be higher. Pregnancy, breastfeeding and plans to become pregnant should also be discussed with a diabetes clinician.

Many medicines can change blood glucose levels or alter the effect of insulin. Other diabetes medicines may increase the risk of hypoglycemia. Medicines such as corticosteroids, some diuretics, thyroid hormones and certain antipsychotic medicines may raise blood glucose and affect insulin requirements. Beta-blockers and some other medicines can make warning signs of hypoglycemia less noticeable. Alcohol can also unpredictably increase or decrease blood glucose.

Using a thiazolidinedione medicine, such as pioglitazone, with insulin may contribute to fluid retention and can worsen or lead to heart failure in some people. Patients should give their prescriber and pharmacist a complete list of prescription medicines, non-prescription products, vitamins and herbal supplements. They should not start, stop or change a medicine because of a potential interaction without professional guidance.

Safe Use, Storage and Monitoring

Lantus is injected under the skin, usually in the abdomen, thigh or upper arm. It must not be injected into a vein or used in an insulin pump. It should not be mixed or diluted with another insulin or solution unless a qualified clinician specifically directs otherwise. The product should be checked before use; it should be clear and colorless, and it should not be used if it looks cloudy, colored or contains particles.

Injection sites should be rotated within the chosen area rather than repeatedly using the same exact spot. Pens and needles must never be shared, even when a new needle is used, because sharing can transmit blood-borne infections. Patients should use a new needle for each injection and dispose of sharps safely according to local guidance. Storage instructions differ for unopened and in-use pens or vials, so the package leaflet and pharmacist are important sources of product-specific information.

Regular blood glucose checks help a person and their care team recognize patterns and adjust treatment safely. Illness, travel, changes in meals, exercise, stress and other medicines can all affect glucose control. Lantus doses are individualized; patients should contact their clinician, diabetes educator or pharmacist for instructions about a missed dose, an unexpected glucose result or any dosing question rather than making unplanned changes.

Reducing the Risk of Low Blood Sugar

People using insulin benefit from having a personal plan for recognizing and treating low blood sugar. A clinician may recommend carrying a quick source of carbohydrate and informing close family members, friends, school staff or colleagues about the signs of hypoglycemia. The appropriate response depends on the person’s glucose reading, symptoms and individual diabetes plan.

It is particularly important to check blood glucose as advised before driving, operating machinery or doing activities where impaired concentration could be dangerous. Severe hypoglycemia can affect thinking, coordination and consciousness. Patients and caregivers may be prescribed glucagon for severe episodes; they should receive training on when and how to use it. Following the prescribed meal plan and discussing planned changes in exercise can further support safer insulin use.

When to Seek Medical Care

Emergency care is needed for severe hypoglycemia, especially if a person is unconscious, having a seizure, unable to swallow safely, very confused or not improving with the treatment plan provided by their clinician. Emergency help is also needed for signs of a serious allergic reaction, including breathing difficulty, swelling of the lips, tongue or throat, fainting, or widespread hives.

A clinician should be contacted promptly for repeated low blood sugar episodes, persistent high blood glucose, worsening injection-site changes, new or increasing swelling, rapid weight gain, shortness of breath, or any concern about a medicine interaction. Lantus should not be stopped or its dose changed without medical advice, as stopping insulin can lead to dangerously high blood glucose. Acibadem International’s multidisciplinary specialists and JCI-accredited hospitals can assess diabetes treatment needs for international patients.

Frequently asked questions

What is the most common side effect of Lantus?

Low blood sugar, or hypoglycemia, is the most important and commonly reported side effect of insulin treatment, including Lantus. Symptoms can include sweating, shaking, hunger, dizziness, headache, rapid heartbeat or confusion. A person should follow their clinician's plan for checking and treating low blood sugar.

Does Lantus cause weight gain?

Weight gain can occur with insulin treatment, including Lantus. This may happen as blood glucose control improves and the body is able to use and store glucose more effectively. New or rapid weight gain with swelling or breathlessness should be discussed promptly with a clinician.

Can Lantus cause allergic reactions?

Injection-site itching, redness or rash can occur and may be mild. Rarely, a serious allergic reaction can cause widespread hives, swelling, breathing problems, sweating or light-headedness. These severe symptoms require emergency medical attention.

Can Lantus be mixed with other insulin?

Lantus should not be mixed or diluted with another insulin or solution. Mixing may change how insulin glargine works and can affect blood glucose control. Patients should use it only as directed in the product information and by their prescribing clinician.

What medicines can interact with Lantus?

Many medicines can affect blood glucose or change the risk of hypoglycemia, including other diabetes medicines, corticosteroids, certain diuretics and beta-blockers. Alcohol can also alter glucose levels. A pharmacist or clinician should review all medicines and supplements when Lantus is prescribed or changed.

Should a person change their Lantus dose if they are sick or eating less?

Illness and reduced food intake can change blood glucose levels and insulin needs, but a person should not make unplanned dose changes. They should follow their sick-day plan if they have one and contact their diabetes clinician for individualized guidance. Urgent care may be needed for persistent vomiting, dehydration, very high glucose or symptoms of diabetic ketoacidosis.

References

• U.S. Food and Drug Administration
• American Diabetes Association
• National Institute of Diabetes and Digestive and Kidney Diseases
• MedlinePlus
• Lantus Prescribing Information

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.