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Antidiabetic / long-acting (basal) insulin

Insulin glargine: uses, side effects & precautions

Also known as Lantus, Toujeo, Basaglar, Semglee, Abasaglar.

This information is for general guidance only and does not constitute medical advice. Always consult a qualified healthcare professional for personal medical concerns. In an emergency, call your local emergency number.

What it is used for

  • Type 1 diabetes (background insulin)
  • Type 2 diabetes (background insulin when other treatments are not enough)

How it works

Insulin glargine is a slow, steady ('basal') form of insulin that works over about a day to keep background blood sugar controlled between meals and overnight by helping cells take up glucose.

How it is taken

Given as an injection under the skin (subcutaneous) using a pen or vial and syringe, usually around the same time each day. Injection sites are rotated to protect the skin. Use it exactly as your doctor or diabetes nurse shows you and as the label directs; never share pens or needles.

No doses here on purpose. The right strength and schedule depend on you — only a doctor or pharmacist should set them. Always follow your prescription and the label.

Common side effects

  • Low blood sugar (hypoglycaemia)
  • Redness, swelling, or itching at the injection site
  • Skin thickening or lumps if the same spot is used repeatedly
  • Weight gain

Serious effects — get help

  • Severe low blood sugar with confusion, seizures, or loss of consciousness — emergency care needed
  • Severe allergic reaction (widespread rash, swelling, trouble breathing)
  • Very low potassium levels (uncommon) causing muscle weakness or irregular heartbeat

If a reaction is severe — for example trouble breathing, swelling of the face or throat, or collapse — go to the nearest emergency room now or call your local emergency number. Do not wait for an online consultation.

Interactions to watch

  • Other diabetes medicines (added low-blood-sugar risk)
  • Alcohol (can cause unpredictable blood sugar)
  • Steroids and some blood-pressure medicines (can raise or lower blood sugar)
  • Beta-blockers (may hide warning signs of low blood sugar)

Who should take care

  • Do not mix glargine with other insulins in the same syringe unless told to
  • Learn to recognise and treat low blood sugar, and carry a fast-acting sugar source
  • Discuss dose timing with illness, travel, or changes in activity or diet
  • Tell your care team if pregnant, breastfeeding, or planning pregnancy, as insulin needs change
  • Store as directed and check the insulin looks clear before use

Frequently asked questions

Is glargine the same as fast-acting insulin?
No. Glargine is long-acting background insulin. Fast-acting (mealtime) insulins work quickly to cover food. Many people use both — never swap one for the other.
Where do I inject it?
Under the skin of the abdomen, thigh, or upper arm, rotating sites each time to avoid skin lumps. Your diabetes nurse will show you the technique.
What if I forget a dose?
Insulin timing matters — contact your diabetes team or follow the personalised plan they gave you rather than guessing. Do not double up.
Can my insulin needs change?
Yes. Illness, stress, activity, diet, weight, and pregnancy can all change how much you need. Your care team adjusts the dose; do not change it on your own.
Is Insulin glargine safe to take?
For most people it is safe when taken exactly as a doctor or pharmacist advises and as printed on the label. Tell your clinician about your other medicines and health conditions, and seek urgent care for any serious reaction.

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