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.

Last updated: October 2026 · Based on ADA Standards of Care, FDA prescribing information, and NIDDK · General information, not medical advice — see our editorial policy

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.

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 in most U.S. states human regular insulin can be bought without a prescription (for example, under Walmart's ReliOn brand) — though using it safely still needs a plan from your clinician. 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 about 4–12 hours after injection, so it can be timed to cover meals as well as provide background coverage. NPH is usually taken once or twice a day. It is also low-cost and available without a prescription in most 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 U-100 lasts about 24 hours; detemir lasts up to about 24 hours depending on the dose and is often given twice a day. Glargine U-300 lasts up to about 36 hours, and degludec is the longest-lasting daily insulin, with an effect that persists for 42 hours or more. These longer insulins have an even flatter profile, which generally means a lower risk of low blood sugar overnight and more flexibility in dose timing. (Detemir, sold as Levemir, was discontinued in the U.S. in 2024; it is still sold in some other countries.)

Once-weekly basal insulins are a newer option. Insulin icodec (Awiqli) and insulin efsitora alfa (Onswik) are FDA-approved for adults with type 2 diabetes and are injected once a week. They are not approved in the U.S. for type 1 diabetes, and moving between a daily and a weekly insulin is planned by the prescriber.

The long-acting insulin comparison goes into more detail on each basal insulin, including once-weekly insulin.

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. See the full inhaled insulin guide.

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 insulin glargine-yfgn (formerly sold as Semglee), Rezvoglar, and Langlara. Glargine-yfgn was the first product approved as interchangeable in the United States, meaning a pharmacist may substitute it for Lantus without calling the prescriber where state law allows. Basaglar is a closely related "follow-on" glargine that was approved through a different pathway and is not classed as a biosimilar. Insulin aspart now has biosimilars too: Merilog (approved 2025) and Kirsty (approved 2025, the first interchangeable with NovoLog).

"Unbranded" or authorized-generic insulins are the same product as a brand-name insulin, sold under the generic name by the same manufacturer, usually at a lower list price. Insulin lispro and insulin aspart are sold this way in the U.S.; glargine is available as several lower-cost biosimilars and unbranded versions. Cost differences can be substantial — see the cost and access page for more.

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