Rapid, short, intermediate and long-acting types · Written by the Lyng Pharmacy team, based on NHS and BNF guidance · Updated August 2026
Also sold asLantus, Levemir, Tresiba, NovoRapid, Humalog, Humulin
Type of medicineInsulin
Available asPre-filled pens, cartridges, vials, pumps
How you get itPrescription only
Insulin replaces the hormone the body cannot make or cannot use properly. It is essential in type 1 diabetes and used in some type 2. The medicine itself is straightforward; the safety sits in the detail — the right pen, the right site, and knowing exactly what to do about a hypo.
The types
Rapid-acting (aspart, lispro, glulisine) — works within about 15 minutes, taken with meals
Short-acting (soluble human insulin) — taken around 30 minutes before meals
Intermediate-acting (isophane/NPH) — lasts around 12 to 18 hours
Long-acting (glargine, detemir, degludec) — background cover, once or twice daily
Mixed — a fixed combination in one pen
Different insulins are not interchangeable. Always check the name and strength on the pen before injecting, and never assume a new box is the same as the last. Some insulins come in 100 units/ml and others in 200 or 300 units/ml.
Injecting properly
Inject into the fat under the skin of the stomach, thigh, buttock or upper arm. Rotate the site every time — injecting repeatedly into one spot causes lipohypertrophy, lumpy areas where insulin absorbs unpredictably, which is a common hidden cause of erratic control.
Use a new needle for each injection, and count to ten before withdrawing the pen so the full dose goes in.
Store unopened pens in the fridge. In use, most pens stay at room temperature for around four weeks — check your leaflet. Never freeze insulin, and never share a pen even with a new needle.
Treat immediately with fast-acting sugar — glucose tablets, 150ml of ordinary fizzy drink or fruit juice — then a longer-acting carbohydrate. Recheck after 15 minutes and repeat if still low. Carry hypo treatment with you at all times.
If you drive, you must tell the DVLA. Test your blood glucose no more than two hours before driving and every two hours on long journeys, and keep glucose within reach in the car — not the boot. Do not drive if your reading is below 5 mmol/L without treating first.
Sick day rules
Never stop your insulin because you are unwell and not eating, particularly in type 1 diabetes. Illness usually raises blood glucose, and stopping insulin can lead to diabetic ketoacidosis, which is life-threatening.
When ill: test more often, keep drinking fluids, check ketones if you have been told to, and follow the sick day plan from your diabetes team. Seek help if you cannot keep fluids down, ketones are raised, or glucose stays high despite correction doses.
Always read the label. This page is general information, not advice for your situation. Doses, warnings and interactions differ between products and between people. Check the leaflet inside your medicine, and ask our pharmacist if anything is unclear — that conversation is free and takes two minutes.
Questions about Insulin?
1 Lyng Lane, West Bromwich B70 7RW · Mon–Fri 8:30am–6pm, Sat 9am–1pm · 0121 500 5756
No — particularly in type 1 diabetes. Illness usually raises blood glucose, and stopping insulin can cause life-threatening diabetic ketoacidosis. Follow your sick day plan.
Why do I need to rotate injection sites?
Repeated injecting into one spot causes lumpy areas where insulin absorbs unpredictably — a common hidden cause of erratic blood sugar.
Do I need to tell the DVLA I use insulin?
Yes. You must also test before driving and every two hours on long journeys, and keep glucose within reach in the car.
Can I share an insulin pen?
Never, even with a new needle. Pens are for one person only because of infection risk.
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