Comparing and Contrasting Long-acting Insulins

by Jessica Pyhtila, PharmD, BCPS, BCGP

If your doctor has told you that you need long-acting insulin, you may be overwhelmed with the number of products available. Although many brand name long-acting insulins are advertised on TV and in print, they represent only three main insulin products. The three main long-acting insulins that are available in the United States are insulin glargine (Lantus, Basaglar, Semglee, Toujeo), insulin degludec (Tresiba) and insulin detemir (Levemir).

In this article, we will explore the similarities and differences between the long-acting insulins to help give you a better idea of what to expect.

How Does Long-acting Insulin Work?

Long-acting insulin works by having delayed absorption. In other words, the drug does not undergo immediate absorption into the bloodstream. After the long-acting insulin is injected under the skin, it forms a substance that slowly releases the insulin into the bloodstream. This prevents a sudden dump of long-acting insulin that could otherwise drive your blood sugar down.

All long-acting insulins work in similar ways, although their chemical properties vary. For example:

  • Insulin glargine (Lantus, Basaglar, Semglee, Toujeo) forms microprecipitates – similar to tiny crystals – under the skin that slowly dissolve
  • Insulin degludec (Toujeo) forms a soluble mass under your skin that releases insulin into your bloodstream over time
  • Insulin detemir (Levemir) forms a complex under your skin that releases insulin into your bloodstream, and also binds to a protein called albumin to slow absorption

Why is Long-acting Insulin Used?

Long-acting insulin is used to mimic the body’s natural production of insulin throughout the day. It is considered “basal” insulin, meaning that it makes up for the insulin your pancreas would normally produce on its own, even when you don’t eat. Basal insulin helps to control the levels of blood sugar that are naturally produced by your body, specifically your liver.

In contrast, short-acting insulin is used to compensate for the spike in insulin production your pancreas would normally make following a meal.

Not everyone with diabetes ends up taking insulin. However, when the pancreas has a difficult time producing enough insulin on its own to meet your body’s needs, using insulin products is one of the best ways to maintain your blood sugar control.

What is the Best Long-acting Insulin?

The best long-acting insulin is highly dependent on your specific needs. For example, although it may seem at first that having a super-long-acting insulin may be beneficial, it can be harmful in people with unpredictable blood sugar swings. Using a long-acting insulin that wears off quicker than others may be beneficial in those cases.

Further, some long-acting insulin products are stronger than others. This means they can be more appropriate for some people than others. For example, Toujeo contains 300 units of insulin per 1mL. In contrast, Lantus contains 100 units of insulin per 1mL. A person who uses only 5 units of long-acting insulin per day may, therefore, be a better candidate for Lantus as the dose may be easier to measure. This means less risk of accidentally taking too much insulin, leading to low blood sugar.

What is the Strongest Long-acting Insulin?

Long-acting insulin comes in different potencies, or strengths. The most potent long-acting insulin is Tresiba, a form of insulin glargine. The following strengths are available for long-acting insulin products:

Long-acting insulin Strength of product (units of insulin per milliliter)
Lantus (insulin glargine) 100 units per mL
Semglee (insulin glargine) 100 units per mL
Basaglar (insulin glargine) 100 units per mL
Toujeo (insulin glargine) 300 units per mL
Tresiba (insulin degludec) 100 units per mL 200 units per mL
Levemir (insulin detemir) 100 units per mL

Does Long-acting insulin Come in a Pen or in Vials?

Depending on the product, long-acting insulin may be available in a prefilled pen, a vial, or both. Prefilled pens usually require only an insulin pen needle to be injected. Meanwhile, vials require a syringe with a needle.

Long-acting insulin Available in a pen Available in a vial
Lantus (insulin glargine) X X
Semglee (insulin glargine) X X
Basaglar (insulin glargine) X  
Toujeo (insulin glargine) X  
Tresiba (insulin degludec) X X
Levemir (insulin detemir) X X

How Long Does Long-acting Insulin Last?

The amount of time long-acting insulin lasts is highly variable and depends on the person using it. Long-acting insulins tend to start working within about 4 hours of injection, and will wear off many hours later. Generally, although they are sometimes advertised as once-daily insulins, neither insulin glargine nor insulin detemir lasts a full 24 hours. However, as a general rule:

Long-acting insulin Duration of action
Lantus (insulin glargine) lasts up to 24 hours
Semglee (insulin glargine) lasts up to 24 hours
Basaglar (insulin glargine) lasts up to 24 hours
Toujeo (insulin glargine) lasts more than 24 hours
Tresiba (insulin degludec) lasts up to 42 hours
Levemir (insulin detemir) lasts 18 to 23 hours

When Should Long-acting Insulin be Given?

Generally, long-acting insulin can be given at any time of the day as long as you stay consistent with how you take it. For example, if you usually take your long-acting insulin in the morning, you should keep taking it in the morning, instead of taking it at different times of the day.

However, because some long-acting insulins can last varying amounts of time, your doctor may instruct you to take it at a specific time of day to avoid low blood sugar. For example, if you sometimes have low blood sugar overnight, your doctor may instruct you to take your long-acting insulin in the morning. Because long-acting insulins like glargine (Lantus) and detemir (Levemir) frequently do not last a full 24 hours, taking them in the morning could help avoid overnight low blood sugars.

Your doctor may sometimes instruct you to inject your long-acting insulin multiple times a day. Usually, long-acting insulin is given no more than twice a day. The reasons you may need to take it more than once a day include:

  • Your insulin dose is high: Your body can only accommodate a certain amount of insulin injected at one time. Although this can vary by person, most people cannot inject more than 3 mL under their skin at one time. For this reason, if you take an extremely high dose of insulin, your doctor may instruct you to split up the doses so that the drug can be more easily absorbed.
  • Your insulin is not lasting as long as expected: In some people, including up to 30% of those with Type 1 diabetes, long-acting insulin does not last as long as expected. These people may notice their blood sugars starting to increase throughout the day. As a result, their doctors may direct them to take their long-acting insulin twice a day. Usually, it is given in the morning upon waking and at bedtime.

Do Long-acting Insulins Come Mixed with Other Medications?

For convenience, some long-acting insulins come mixed with other injectable medications. Currently, there are two products available that combine long-acting insulin with glucagon-like peptide-1 receptor agonists, or GLP-1 agonists:

  • Xultophy: This product combines insulin degludec (Tresiba) with the GLP-1 agonist liraglutide (Victoza, Saxenda). Each millilter of Xultophy contains 100 units of insulin degludec and 3.6 mg of liraglutide. It is usually given once daily.
  • Soliqua: This product combines insulin glargine (Lantus, Basaglar, Semglee, Toujeo) with the GLP-1 agonist lixisenatide (Adlyxin). Each milliliter of Soliqua contains 100 units of insulin glargine and 3 micrograms of lixisenatide. The drug is usually given once a day.


Haahr, Hanne; Heise, Tim. “A Review of the Pharmacological Properties of Insulin Degludec and Their Clinical Relevance.” Clinical Pharmacokinetics, September 2, 2014. Retrieved from

Havelund, Svend; Plum, Anne; Ribel, Ulla; et al. “The mechanism of protraction of insulin detemir, a long-acting, acylated analog of human insulin.” Pharmaceutical Research, August 2004. Retrieved from

Watson, Stephanie. “Long-Acting Insulin: How It Works.” Healthline, September 27, 2019. Retrieved from:

ClinCalc. “Is there a maximum insulin glargine (Lantus) dose?” October 15, 2012. Retrieved from:

Leave a Reply

Your email address will not be published. Required fields are marked *