Insulins are grouped by how quickly they start working, when they peak, and how long they last. The main categories are rapid-acting, short-acting (regular), intermediate-acting (NPH), long-acting, ultra-long-acting, premixed combinations, and concentrated formulations. Modern basal-bolus regimens combine a long-acting basal with a rapid-acting mealtime insulin, while simpler or cost-sensitive regimens may use NPH and regular insulin twice daily.
The Pharmacokinetic Profile of Insulins
| Category | Examples (Brand) | Onset | Peak | Duration |
|---|---|---|---|---|
| Rapid-acting | Lispro (Humalog), aspart (NovoLog), glulisine (Apidra) | 10-20 min | 1-2 hr | 3-5 hr |
| Ultra-rapid-acting | Faster aspart (Fiasp), lispro-aabc (Lyumjev) | 2-5 min | 1 hr | 3-5 hr |
| Short-acting (regular) | Humulin R, Novolin R | 30 min | 2-4 hr | 6-8 hr |
| Intermediate-acting | NPH (Humulin N, Novolin N) | 1-2 hr | 4-10 hr | 10-16 hr |
| Long-acting | Glargine U-100 (Lantus, Basaglar, Semglee), detemir (Levemir) | 1-2 hr | Minimal peak | 20-24 hr |
| Ultra-long-acting | Degludec (Tresiba), glargine U-300 (Toujeo) | 1-2 hr | No clinical peak | 24-42 hr |
| Premixed | 70/30, 75/25, 50/50 (Humulin, Novolin, Humalog Mix, NovoLog Mix) | 10-30 min | Dual peaks | 10-16 hr |
| Concentrated | Humulin R U-500, Humalog U-200, Tresiba U-200, Toujeo U-300 | Varies | Varies | Varies |
Rapid-Acting Analogs
Rapid-acting insulins cover meals and correct high glucose readings. They work within 10 to 20 minutes, peak around 1 to 2 hours, and clear in 3 to 5 hours.
- Lispro (Humalog, Admelog): dosed 10 to 15 minutes before meals
- Aspart (NovoLog, Fiasp): Fiasp starts faster (2 to 5 min) and can be dosed with or just after meals
- Glulisine (Apidra): similar profile to lispro and aspart
- Lyumjev (lispro-aabc): ultra-rapid variant of lispro
These are used in basal-bolus regimens, in insulin pumps, and for “correction” doses.
Short-Acting (Regular) Insulin
Regular human insulin (Humulin R, Novolin R) has been in use since 1982. It starts working in 30 minutes, peaks at 2 to 4 hours, and lasts 6 to 8 hours. It is less convenient than rapid-acting analogs but remains cheaper and is still used:
- In some cost-sensitive outpatient regimens
- In hospital IV drips for high glucose or DKA
- In older premixed products
- In the concentrated U-500 form for severe insulin resistance
Intermediate-Acting (NPH) Insulin
NPH (neutral protamine Hagedorn) is a cloudy suspension that extends insulin duration by binding it to protamine. It starts at 1 to 2 hours, peaks at 4 to 10 hours, and lasts 10 to 16 hours. Common uses:
- Twice-daily NPH plus regular insulin as an older basal-bolus regimen
- Premixed with regular or rapid-acting insulin
- Overnight basal coverage when cost is a barrier
NPH must be resuspended before each injection by gently rolling the vial or pen. Its pronounced peak produces more hypoglycemia than modern basal analogs.
Long-Acting Basal Analogs
Long-acting insulins provide steady background coverage with minimal peak:
- Glargine U-100 (Lantus, Basaglar, Semglee): 20 to 24 hours; usually once daily. Semglee is the first FDA-approved interchangeable biosimilar insulin.
- Detemir (Levemir): 12 to 24 hours (dose-dependent); sometimes twice daily at lower doses.
These replaced NPH for most outpatient basal coverage because of lower hypoglycemia risk.
Ultra-Long-Acting Basal Analogs
- Degludec (Tresiba): half-life ~25 hours; duration up to 42 hours; very flat profile; allows some flexibility in injection timing.
- Glargine U-300 (Toujeo): concentrated glargine with slower release; 24 to 36 hours; less injection-site discomfort because volume is smaller.
These are preferred when day-to-day basal timing varies or when U-100 glargine duration falls short.
Premixed Insulins
Premixed insulins combine intermediate or basal insulin with rapid or short-acting insulin in a single pen or vial. Common ratios:
- 70/30 (70% NPH, 30% regular) — Humulin 70/30, Novolin 70/30
- 70/30 (70% aspart protamine, 30% aspart) — NovoLog Mix 70/30
- 75/25 (75% lispro protamine, 25% lispro) — Humalog Mix 75/25
- 50/50 ratios for patients needing more prandial coverage
Premixed regimens are simpler (twice-daily dosing at breakfast and dinner), which helps adherence — but offer less flexibility than separate basal and bolus dosing.
Concentrated Insulins
For patients needing large insulin doses, concentrated products deliver more units in less volume:
- Humulin R U-500: 5x concentrated regular insulin; typically given 2 to 3 times daily in severe insulin resistance
- Humalog U-200: 2x concentrated lispro
- Tresiba U-200: 2x concentrated degludec
- Toujeo U-300: 3x concentrated glargine
Concentrated insulins require different pen dosing and should never be transferred to a standard U-100 syringe without dose calculations.
How to Think About Choosing
- Type 1 diabetes: basal-bolus with a long- or ultra-long-acting basal plus rapid-acting mealtime insulin, or a closed-loop pump using rapid-acting only.
- Type 2 diabetes starting insulin: usually once-daily basal (glargine, detemir, degludec) added to oral agents.
- Type 2 progressing on basal: add a bolus at the largest meal (basal-plus), then at all meals (basal-bolus).
- Cost-sensitive care: NPH with regular insulin, or a 70/30 premixed regimen, twice daily.
- Severe insulin resistance: U-500 regular insulin or concentrated basal options.
- Frequent hypoglycemia: switch NPH to a long-acting analog; consider degludec for flatter profile.
Related Reading
For broader treatment context, see our treatment hub, and for how insulin fits alongside other drugs in diabetes care, our guide to A1C levels covers the targets insulin is dosed to reach.
The Bottom Line
Insulin is not a single drug — it is a class of products with very different onset, peak, and duration profiles. Choosing the right type depends on whether you need basal coverage, meal coverage, or both; your A1C target; your lifestyle; whether you have severe insulin resistance; and cost constraints. Work with your diabetes team or endocrinologist to match the insulin to your pattern rather than defaulting to whatever your last doctor prescribed, because small changes in type and timing often produce big improvements in time-in-range.
