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Insulin

Types of Insulin: Which One and Why

Not all insulins are the same. Understanding the difference between rapid, long-acting, and mixed insulins helps you manage your blood sugar effectively and safely.

Written and clinically reviewed by Suman Konda, PharmD, Clinical Pharmacist · Editorial policy · Not medical advice

Last reviewed and updated: · How we check our content

Types
Rapid, Short, Intermediate, Long, Mixed
Fastest acting
Novorapid / Humalog
Longest acting
Tresiba (42h)
Key monitoring
Blood glucose + HbA1c

The 5 Types of Insulin

TypeExamplesOnsetPeakDuration
Rapid-actingNovoRapid, Humalog, Apidra10–15 min1–2 hours3–5 hours
Short-acting (soluble)Actrapid, Humulin S30–60 min2–4 hours6–8 hours
Intermediate-actingInsulatard, Humulin I1–3 hours4–8 hours12–18 hours
Long-acting (basal)Lantus, Levemir, Tresiba1–2 hoursFlat / none20–42 hours
MixedNovoMix 30, Humulin M315–30 min1–4 hours12–18 hours

Basal-Bolus Regimen (Type 1 Diabetes)

The most physiological insulin regimen mimics the body's natural insulin secretion:

  • Basal insulin (once or twice daily): Provides background insulin, e.g. Lantus at bedtime
  • Bolus insulin (with each meal): Rapid-acting insulin to cover carbohydrate content, e.g. NovoRapid with each meal
  • Correction doses: Extra bolus to bring high blood sugar back to target
Hypoglycaemia RiskThe most dangerous side effect of insulin is hypoglycaemia (low blood sugar). Know the signs: shaking, sweating, confusion, rapid heartbeat. Treat with 15 g fast-acting carbohydrate (3–4 glucose tablets or a small glass of juice). Always carry glucose.

Injection Sites and Rotation

SiteAbsorption SpeedBest For
AbdomenFastestRapid-acting insulin (meal boluses)
Outer thighMediumLong-acting basal insulin
Outer upper armMediumCan be used for both
ButtockSlowestLong-acting, least variation
Lipohypertrophy WarningAlways rotate injection sites. Injecting repeatedly in the same spot causes fat to build up (lipohypertrophy): this slows insulin absorption and makes blood sugar control unpredictable.
Should I take rapid insulin before or after food?
Rapid-acting insulin should normally be taken immediately before a meal (10–15 minutes before for Humalog/NovoRapid). Some people take it after eating if they're unsure how much they'll eat: discuss with your diabetes team.
My blood sugar is always high in the morning: why?
Fasting morning hyperglycaemia is usually due to insufficient basal insulin, the dawn phenomenon (cortisol-driven glucose release), or post-hypoglycaemia rebound. Review your long-acting dose with your diabetes nurse.
Can insulin be taken by mouth?
No. Insulin is destroyed by stomach acid. It must be injected or delivered via pump. Inhaled insulin (Afrezza) exists but is not widely available.

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Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.