Insulin Clinics / Foundations
Types of insulin
Insulins are grouped by how fast they start working and how long they last. Most regimens combine a long-acting "background" insulin with a faster one taken at meals.
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The categories at a glance
Three numbers describe every insulin:
- Onset — how long after the injection it starts to lower blood sugar.
- Peak — when its effect is strongest. Some newer insulins have very little peak.
- Duration — how long it keeps working.
The numbers below are typical ranges from manufacturer prescribing information and consensus references. Real-world timing varies between people, with the dose, the injection site, body temperature, and activity. Treat them as a guide, not a stopwatch.
| Type | Examples (generic / brand) | Onset | Peak | Duration | Typical role |
|---|---|---|---|---|---|
| Rapid-acting | lispro (Humalog, Admelog), aspart (Novolog), glulisine (Apidra) | ~15 min | 1–2 hr | 3–5 hr | Mealtime (bolus); correction doses |
| Ultra-rapid | faster aspart (Fiasp), lispro-aabc (Lyumjev) | ~2–5 min | ~1 hr | 3–5 hr | Mealtime; pumps; closer to natural pattern |
| Short-acting (regular) | regular human insulin (Humulin R, Novolin R) | ~30 min | 2–4 hr | 5–8 hr | Mealtime when taken 30 min before eating; lower-cost option |
| Intermediate | NPH (Humulin N, Novolin N) | 1–2 hr | 4–8 hr | 10–16 hr | Background coverage, often twice daily; lower-cost option |
| Long-acting | glargine U-100 (Lantus, Basaglar, Semglee), detemir (Levemir) | 1–2 hr | Minimal | ~20–24 hr | Once or twice daily basal |
| Ultra-long-acting | degludec (Tresiba), glargine U-300 (Toujeo) | 1–2 hr | Minimal | ≥24–42 hr | Once daily basal; flatter, more forgiving timing |
| Premixed | 70/30 NPH+regular, 75/25 or 50/50 lispro mix, 70/30 aspart mix | ~15–30 min | Dual | 10–16 hr | Two daily injections covering basal + mealtime in one pen |
Rapid- and ultra-rapid-acting insulins
These are taken at meals to cover the rise in blood glucose from food. Standard rapid-acting insulins (lispro, aspart, glulisine) are typically injected within about 15 minutes of the first bite. The ultra-rapid versions (faster aspart, lispro-aabc) absorb faster and can be given right at mealtime, or within 20 minutes after starting to eat — useful when appetite is unpredictable, such as in young children or older adults.
Rapid-acting insulin is also what most people use for "correction" doses — small extra amounts to bring down a high reading. It is the type most insulin pumps use.
Short-acting (regular) insulin
Regular human insulin was the standard mealtime insulin for decades. It works more slowly than the analog rapid insulins, so it usually needs to be taken about 30 minutes before eating. It is significantly cheaper and is sold over the counter in many U.S. states under the ReliOn brand at Walmart. For some people, especially those paying out of pocket, regular insulin remains a practical choice — but the timing is less forgiving and the risk of post-meal lows is higher.
Intermediate-acting (NPH)
NPH is regular human insulin combined with protamine, which slows absorption. It has a clear peak 4–8 hours after injection, so it can be timed to cover meals as well as provide background coverage. NPH is usually taken twice a day. It is also low-cost and available without a prescription in many U.S. states. Because of its peak, it carries a higher risk of overnight hypoglycemia than the long-acting analogs, especially when dosed at dinner.
Long-acting and ultra-long-acting (basal) insulins
Basal insulins provide steady background coverage between meals and overnight. Glargine and detemir last roughly 20–24 hours. Degludec and glargine U-300 last longer (over 24 hours, up to about 42 for degludec) and have an even flatter profile, which generally means a lower risk of low blood sugar overnight and more flexibility in dose timing.
For people with type 2 diabetes who start insulin, a single daily basal injection is the most common starting point. For type 1 diabetes, basal is paired with rapid-acting insulin at meals, or delivered continuously through a pump.
Premixed insulins
Premixed insulins combine a basal and a mealtime insulin in one pen. The numbers (70/30, 75/25, 50/50) describe the ratio of intermediate or protamine-bound insulin to rapid or short-acting. They are usually taken twice a day, before breakfast and dinner. Premixes simplify the regimen — fewer injections, fewer decisions — but offer less flexibility for varying meal sizes or unusual schedules.
Inhaled insulin
Inhaled insulin (Afrezza) is a powdered rapid-acting insulin breathed in through a small inhaler at the start of a meal. It works very quickly and is gone within a few hours. It is not used for basal coverage and is not appropriate for people with chronic lung disease such as asthma or COPD. It is covered briefly here and in more depth on the delivery methods page.
U-100, U-200, U-300, U-500: what the numbers mean
The "U" stands for units of insulin per milliliter. U-100, the standard, contains 100 units in every milliliter of liquid. Most insulins, syringes, and pens are calibrated to U-100.
Higher-concentration insulins exist for people who need very large doses. Glargine U-300 (Toujeo) packs three times the insulin into the same volume; degludec is also available in U-200. These are dosed in units, not volume — the pen counts units, regardless of concentration. U-500 regular insulin is reserved for people with severe insulin resistance who would otherwise need very large injection volumes; it requires careful prescribing because mix-ups with U-100 syringes have caused serious overdoses.
Biosimilars and authorized generics
Insulin is a biologic — a protein made by living cells — so there are no true generics. Instead, there are biosimilars, which are highly similar versions of an approved insulin made by another manufacturer. Insulin glargine has biosimilar versions including Basaglar and Semglee; Semglee was the first product approved as interchangeable in the United States, meaning a pharmacist may substitute it for Lantus without calling the prescriber.
"Authorized generics" are the same product as the brand-name insulin, sold under a generic label by the same manufacturer at a lower price. Lispro, aspart, and glargine all have authorized generics now. Cost differences can be substantial — see the cost and access page for more.