Insulin Clinics / Foundations
Long-acting (basal) insulin compared
Basal insulins provide the steady background insulin your body needs around the clock. They differ mainly in how long they last, how flat their action is, and how much they cost.
Last updated: October 2026 · Based on ADA Standards of Care, FDA prescribing information, and NIDDK · General information, not medical advice — see our editorial policy
What basal insulin does
Even when you are not eating, your liver releases glucose into the blood to keep the brain and body fueled. In people without diabetes, a small, steady amount of insulin keeps that release in check. Basal (background) insulin does the same job for people with diabetes: it is meant to keep glucose steady overnight and between meals, not to cover food.
Most people who start insulin for type 2 diabetes start with a basal insulin. People with type 1 diabetes use basal insulin alongside mealtime insulin, or get basal delivery from a pump using rapid-acting insulin.
Basal insulins compared
Durations are typical values from prescribing information and clinical references; individual responses vary. In-use periods (how long a pen or vial lasts at room temperature once in use) are approximate — always check your package insert.
| Insulin | Examples | Duration | Typical schedule | In-use period |
|---|---|---|---|---|
| Glargine U-100 | Lantus, Basaglar, Rezvoglar, Langlara, insulin glargine-yfgn (formerly sold as Semglee), unbranded glargine | ~24 hr | Once daily, same time each day | ~28 days |
| Glargine U-300 | Toujeo | Up to ~36 hr | Once daily | ~56 days |
| Degludec (U-100, U-200) | Tresiba | 42 hr or more | Once daily | ~56 days |
| Detemir | Levemir (discontinued in the U.S. in 2024; still sold in some other countries) | Up to ~24 hr, dose-dependent | Once or twice daily | ~42 days |
| Once-weekly basal (type 2 diabetes, adults) | Awiqli (icodec), Onswik (efsitora alfa) | About a week | Once weekly, same day each week | Check your package insert |
| NPH (intermediate) | Humulin N, Novolin N | ~12–18 hr, peaks at ~4–12 hr | Once or twice daily | Varies widely by product (some pens ~14 days) |
Glargine U-100
Glargine was the first long-acting analog insulin and is still the most widely used. It has a fairly flat profile over about a day. Several versions exist: the original brand (Lantus), a follow-on product (Basaglar), and interchangeable biosimilars (insulin glargine-yfgn, formerly sold as Semglee; Rezvoglar; and Langlara), which a pharmacist may substitute where state law allows. They contain the same insulin molecule at the same concentration, but the pens differ, so ask for a demonstration if your pharmacy switches you.
Glargine U-300
Toujeo is glargine at three times the concentration. The smaller volume forms a more compact deposit under the skin, which releases insulin more slowly and evenly — up to about 36 hours. Units of U-300 are not always interchangeable one-for-one with U-100 glargine: people switching often end up needing a somewhat different number of units, which is why the switch is managed by the prescriber.
Degludec
Degludec (Tresiba) forms chains of insulin molecules under the skin that release slowly, giving the longest action of any daily insulin — 42 hours or more. This is the insulin most often meant by searches for an insulin that "lasts 42 hours." Because of its long tail, it takes a few days to reach a steady level after a dose change, and the prescribing information allows some flexibility in the time of day it is given. It comes in U-100 and U-200 pens; the pen counts units either way.
Detemir
Detemir (Levemir) lasts up to about 24 hours depending on dose and is often given twice a day. Levemir was discontinued in the U.S. in 2024; it is still sold in some other countries. People in the U.S. who used it have been switched to other basal insulins.
NPH
NPH is a human insulin made longer-acting by adding protamine. Unlike the analogs above, it has a definite peak several hours after injection, which raises the risk of lows — especially overnight when taken in the evening. It is much less expensive and is sold without a prescription in most U.S. states, which makes it an important option when cost is a barrier. It must be gently rolled until uniformly cloudy before each dose.
Once-weekly basal insulin
Two basal insulins are injected once a week. Insulin icodec (Awiqli) was approved by the FDA in March 2026, and insulin efsitora alfa (Onswik) in September 2026, both for adults with type 2 diabetes. Neither is approved in the U.S. for type 1 diabetes. Icodec is also approved in other places, including the European Union, Canada, and Japan. Both come as concentrated pens that count in units; never draw them into a syringe. Because their effect lasts days, moving between a daily and a weekly insulin follows a specific plan from your prescriber. Weekly insulins are designed to reduce the number of injections; how they compare with daily basal insulin for low blood sugar risk depends on the type of diabetes and is an active area of study.
Basal insulin combined with a GLP-1 medicine
In some countries, basal insulin is also sold in a fixed-ratio combination pen with a GLP-1 receptor agonist (for example, glargine with lixisenatide). These are used in type 2 diabetes and are prescribed as their own product, with their own dosing instructions.
How a basal insulin is chosen
- Risk of low blood sugar. Flatter, longer-acting insulins (degludec, glargine U-300) tend to cause fewer overnight lows than NPH.
- Cost and coverage. Formularies often favor one glargine product over another; NPH is the lowest-cost option.
- Schedule. People with irregular routines may benefit from the timing flexibility of the longest-acting insulins.
- Dose size. Concentrated pens (U-200, U-300) hold more units and suit people who need large doses.
- Device. Pen design, dial size, and maximum dose per injection differ between products.
Taking basal insulin: general points
- Consistency matters. Most basal insulins are taken at about the same time every day. Morning and bedtime both work for most analogs; what matters is picking a time you will remember.
- Do not mix in a syringe. Glargine, detemir, degludec, and the once-weekly insulins should not be mixed with other insulins in the same syringe.
- Missed doses. What to do depends on the product and on how late you are. Do not double up on your own. Use the instructions in your product's leaflet or your care team's written plan, and call your pharmacist or care team if unsure.
- Fasting readings guide adjustments. Basal doses are usually adjusted based on patterns in fasting glucose over several days — see dosing and adjustment.
- Basal is not for corrections. Extra long-acting insulin is not used to bring down a single high reading; that is the job of correction insulin.
Frequently asked questions
Which insulin lasts 42 hours?
Insulin degludec (Tresiba). Its glucose-lowering effect lasts 42 hours or more, the longest of the daily insulins. Glargine U-300 (Toujeo) lasts up to about 36 hours, and glargine U-100 about 24 hours.
Is it better to take long-acting insulin in the morning or at night?
For glargine and degludec, either time is generally acceptable; consistency matters more. NPH taken in the evening carries a higher risk of overnight lows. Your prescriber will advise based on your readings and routine.
Are Lantus, Basaglar, Semglee, and Rezvoglar the same?
They all contain insulin glargine at U-100 strength. Insulin glargine-yfgn (formerly sold as Semglee), Rezvoglar, and Langlara are approved as interchangeable with Lantus, meaning a pharmacist may substitute them without a new prescription where state law permits. Basaglar is a closely related follow-on glargine but is not designated interchangeable. The pens differ, so ask for a demonstration if your product changes.
Can I switch from one long-acting insulin to another?
Only with your prescriber. Some switches are unit-for-unit, but others — for example between glargine U-100 and U-300, or from twice-daily NPH — often need a dose change and closer monitoring.
Is there a once-a-week insulin?
Yes. In the U.S., two once-weekly basal insulins are FDA-approved for adults with type 2 diabetes: insulin icodec (Awiqli, approved March 2026) and insulin efsitora alfa (Onswik, approved September 2026). Neither is approved in the U.S. for type 1 diabetes. Icodec is also approved in other countries, including the EU, Canada, and Japan. Ask your prescriber whether a weekly insulin suits you.