Insulin: types, how it is used and safety essentials

Insulin is the hormone that lets cells use glucose for energy. In type 1 diabetes the body cannot make it, so it is needed for life. In type 2 diabetes the NHS says insulin is prescribed when other medicines cannot keep glucose in a healthy range, and sometimes only temporarily, for example during pregnancy, illness or soon after diagnosis when glucose is dangerously high. It is also used in gestational diabetes.

Untreated high glucose raises the risk of symptoms and of long-term damage to the heart, kidneys, eyes and nerves, which is why dose planning is a specialist-supported process.

The NHS groups insulin by how fast and how long it works, and lists brand names under each group. Names are included for recognition only and do not imply a recommendation.

• Rapid-acting: Admelog, Apidra, Fiasp, Humalog, Lyumjev, NovoRapid, Trurapi (insulin aspart, lispro or glulisine).

• Short-acting: Actrapid, Humulin S (soluble insulin).

• Intermediate-acting: Humulin I, Insulatard (isophane insulin).

• Long-acting: Abasaglar, Lantus, Levemir, Semglee, Toujeo, Tresiba (glargine, detemir or degludec).

• Biphasic (mixed): Humalog Mix, Humulin M3, NovoMix.

In type 1 diabetes a common pattern is a long-acting background dose plus rapid-acting insulin before meals, known as basal-bolus, which usually involves carbohydrate counting. The NHS says detemir is taken twice daily while glargine and degludec are usually once daily, and rapid-acting insulin is generally taken about fifteen minutes before a meal, with faster brands allowing shorter gaps. In type 2 diabetes, the NHS describes long or intermediate insulin alone once or twice a day, long insulin with mealtime insulin, or mixed insulin one to three times a day.

The NHS notes that Levemir is being discontinued, with supplies expected to last until late 2026, and that people on it should speak to their diabetes team about an alternative.

The NHS says most people use pens or pumps. Pen needles are very small and inject a small amount into the layer of fat under the skin. Pumps give small amounts through the day and night, so a separate long-acting insulin is not needed. Technique steps include fitting a fresh needle, removing air, dialling the dose, injecting slowly and holding for ten seconds. Sites such as the abdomen, outer thighs and buttocks should be rotated to prevent fatty lumps, called lipohypertrophy, which slow absorption. The emc entry for Lantus adds that injection sites must be rotated continually and labels checked to avoid mix-ups between insulin types.

The NHS lists hypo symptoms as sweating, trembling, anxiety, confusion, palpitations, tingling lips, blurred vision, dizziness, hunger and pallor. Treatment is quick-acting sugar such as a small glass of juice, glucose tablets or jelly babies, then rechecking and eating starchy carbohydrate once glucose is above 4 mmol/L. Severe hypos need 999.

Injection-site itching usually settles within a week, bruising is usually minor, and temporary blurred vision can occur early and typically improves within a week or two as glucose stabilises. Rare anaphylaxis needs emergency hospital care.

• Rapid sugar first, then starchy food.

• Do not give food or drink to someone who is unconscious; call 999.

The NHS lists medicines that lower glucose and so add to hypo risk: other diabetes medicines, ACE inhibitors, beta blockers and anabolic steroids including testosterone. Those that raise glucose include thiazide diuretics, steroids such as prednisolone, dexamethasone and hydrocortisone, levothyroxine and contraceptive pills. Beta blockers can reduce awareness of hypo symptoms. Alcohol, especially without food, raises hypo risk.

Illness, stress, exercise, changes in routine, growth, pregnancy and menopause can all change insulin needs, so teams give sick-day plans. If you miss a mealtime dose before eating, the NHS says to speak to your doctor or consider a smaller or correction dose, and never double up.

After a hypo the NHS says not to drive for at least forty-five minutes after you have recovered. Insulin is prescription only. Suspected side effects can be reported through the Yellow Card scheme. Storage details differ by product; for example Lantus pens are refrigerated unopened and kept at room temperature for a limited period once in use, so read the leaflet for your own pen.