Insulin Glargine: Uses, Side Effects & Safety

What it is and what it's used for

Insulin glargine is a long-acting form of insulin called a "basal insulin". It provides a steady, background level of insulin over about 24 hours, mimicking the small continuous amount of insulin a healthy pancreas makes between meals and at night. It is used for the long-term management of blood sugar in adults and children with type 1 diabetes, and in adults with type 2 diabetes when oral medicines alone are not enough — often together with mealtime (short-acting) insulin or other diabetes medicines.

In India, insulin glargine is a prescription-only medicine. It is given as an injection under the skin (subcutaneously), usually once a day at about the same time each day. Because diabetes treatment must be tailored to each person, the type, timing, and dose of insulin are decided only by the treating doctor.

How it works (simple language)

After injection, insulin glargine forms tiny clumps under the skin that dissolve very slowly. This releases small amounts of insulin into the blood steadily over roughly 24 hours, without the sharp "peak" that shorter-acting insulins have. This steady background insulin helps the body use glucose from the blood for energy and keeps blood sugar from rising too high between meals and while sleeping.

Insulin glargine starts working within about 1–2 hours of injection and keeps working for around a full day, which is why it is usually given once daily. It cannot replace the natural quick burst of insulin the body needs after eating, so people with type 1 diabetes (and some with type 2) also need a short-acting mealtime insulin.

Dosage forms available in India (general info only)

Insulin glargine is commonly available in India as a 100 units/ml solution for injection in vials, cartridges for reusable insulin pens, and prefilled disposable pens. Well-known brand names include Lantus, Basaglar (also sold as Basalog), and Glaritus — brands and pack sizes vary by pharmacy.

Never decide the dose yourself from this article. Always follow your doctor's prescription or the directions on the pack, and check with your pharmacist if you are unsure — especially for children, where the dose depends on the child's weight and age.

Side effects

Common: Low blood sugar (hypoglycaemia — shaking, sweating, hunger, dizziness, blurred vision, confusion); redness, swelling, itching, or pain at the injection site; thickening or pitting of the fatty tissue under the skin with repeated use at the same spot (lipodystrophy); mild weight gain; headache.

Serious — seek medical care: Severe hypoglycaemia (confusion, slurred speech, fainting, seizure, unconsciousness); signs of a severe allergic reaction such as widespread rash, swelling of the face, lips or tongue, or difficulty breathing; sudden severe headache, vision changes, or chest pain. Call emergency services immediately if someone with diabetes becomes unconscious — never try to force food or drink into an unconscious person's mouth.

Precautions and warnings

• Learn to recognise and treat low blood sugar. Keep fast-acting sugar (glucose tablets, sugar, fruit juice) with you at all times, and make sure family members know what to do if your blood sugar drops.
• Inject exactly as prescribed. Check the label before every injection — mixing up long-acting and short-acting insulins is a common and dangerous error.
• Rotate injection sites. Use a different spot each time (abdomen, thigh, upper arm) to prevent lumps and skin thickening that can affect how insulin is absorbed.
• Not for diabetic ketoacidosis. Insulin glargine is not suitable for treating diabetic ketoacidosis (DKA); DKA needs urgent hospital treatment.
• Illness, stress, and exercise change insulin needs. Fever, infection, vomiting, or changed activity can raise or lower blood sugar — check blood sugar more often and follow your doctor's "sick-day" advice.
• Tell your doctor about kidney or liver problems, heart failure, or if you are starting or stopping any other medicine.
• Driving safety. Hypoglycaemia can impair judgment and reaction time — check your blood sugar before driving and follow your doctor's advice about driving with diabetes.

Interactions (general)

Many medicines can change how insulin glargine works or affect blood sugar. Some blood pressure medicines (such as beta-blockers like atenolol and metoprolol) can mask the warning signs of low blood sugar, such as a racing heartbeat. Steroids, some diuretics, and thyroid hormones may raise blood sugar, while some medicines used for diabetes and infections may lower it. Alcohol can cause blood sugar to drop, sometimes hours after drinking — be especially cautious. Always tell your doctor about ALL medicines you take, including herbal and ayurvedic products, and never mix or dilute insulin glargine with any other insulin or medicine unless your doctor has specifically told you to.

Pregnancy and breastfeeding (general guidance)

Diabetes management during pregnancy needs close medical supervision. Insulin glargine is often used to control blood sugar in pregnant women with diabetes, because keeping blood sugar well controlled is important for the baby's health — but the type and dose of insulin must be decided by the treating doctor. If you are pregnant, planning pregnancy, or breastfeeding, consult your doctor first; do not change or stop your insulin on your own.

Storage

Store unopened vials, cartridges, and pens in a refrigerator (2–8°C) — never freeze them, and never use insulin that has been frozen. Once in use, most products can be kept at room temperature (below 30°C) for a limited number of weeks — check the pack leaflet. Keep away from direct sunlight and heat, and always keep insulin out of the reach of children. Do not use past the expiry date or if the solution looks cloudy or contains particles (glargine solution should be clear and colourless).

When to see a doctor

See a doctor if: blood sugar readings are repeatedly high or low despite following your treatment plan; you have frequent episodes of hypoglycaemia; injection sites become lumpy, swollen, or infected; you notice swelling of the ankles, sudden weight gain, or vision changes; or you become ill and cannot eat or keep medicines down. Seek emergency care for: unconsciousness or seizure (call emergency services immediately), signs of severe allergy, or symptoms of diabetic ketoacidosis such as fruity-smelling breath, deep rapid breathing, nausea, and abdominal pain.

FAQs

1. What is the difference between insulin glargine and regular insulin?

Insulin glargine is a long-acting "background" insulin that works steadily for about 24 hours with one daily injection, while regular (short-acting) insulin works for a few hours and is taken at mealtimes to cover food. Many people need both. They must not be mixed up — always check the label before injecting.

2. Can I skip a dose of insulin glargine if my blood sugar looks normal?

No. Never skip or change a dose without your doctor's advice. Insulin glargine works in the background and cannot be judged by a single reading; missing doses can cause blood sugar to rise dangerously. If you miss a dose, contact your doctor or pharmacist for guidance.

3. What should I do if I take too much insulin glargine?

Taking too much insulin can cause low blood sugar, which can be dangerous. If you realise you have injected extra, monitor your blood sugar closely, have fast-acting sugar ready, and contact your doctor or emergency services. Severe hypoglycaemia needs urgent medical help.

4. Why must I rotate injection sites?

Injecting repeatedly in the same spot can cause lumps or dents in the fatty tissue (lipodystrophy), which makes insulin absorb unevenly and can lead to unpredictable blood sugar. Rotating between areas like the abdomen, thighs, and upper arms keeps absorption steady.