Insulin degludec is an ultra-long-acting basal insulin used to manage blood sugar in people with type 1 and type 2 diabetes. Sold under the brand name Tresiba, it stands out from older long-acting insulins because of its unusually long half-life (over 25 hours) and a glucose-lowering effect that extends beyond 42 hours after a single dose. This gives it one of the flattest, most stable activity profiles of any basal insulin available.
How Insulin Degludec Works
When you inject insulin degludec under the skin, its molecules link together into long, soluble chains called multi-hexamers. These chains form a small depot at the injection site. Over time, individual insulin molecules slowly break away from the chains and enter your bloodstream, where they also attach to a protein in the blood called albumin. Both of these steps slow down absorption, which is why the insulin reaches your system gradually rather than in a burst.
The result is a smooth, steady supply of background insulin with very little fluctuation from hour to hour. That consistency matters because large swings in insulin levels are what cause unexpected drops in blood sugar, especially overnight.
How It Compares to Insulin Glargine
Insulin glargine (Lantus, Basaglar, Toujeo) is the most commonly prescribed long-acting basal insulin, so most people considering degludec want to know how the two stack up. In head-to-head trials, both insulins produce equivalent A1C reductions, meaning they’re equally effective at overall blood sugar control. The differences show up in consistency and safety.
Degludec has lower day-to-day variability in its glucose-lowering effect, which translates to fewer hypoglycemic episodes. In the SWITCH 2 trial, a large randomized study in people with type 2 diabetes, the rate of nighttime low blood sugar episodes was 55.2 per 100 patient-years with degludec compared to 93.6 per 100 patient-years with glargine. That’s roughly a 42% lower rate. The proportion of patients who experienced any nighttime low was 9.7% on degludec versus 14.7% on glargine.
In people with type 1 diabetes who had not previously used insulin, degludec also produced greater reductions in fasting blood sugar and required lower total daily insulin doses compared to glargine.
Dosing Flexibility
Because degludec’s activity stretches well beyond 24 hours, it offers more flexibility in when you take your daily injection. If you normally inject at 8 a.m. but sleep in one day and inject at noon instead, the overlap from the previous dose keeps your background insulin coverage intact. Most other long-acting insulins need to be taken at roughly the same time each day to avoid gaps or stacking.
This flexibility can be genuinely useful for people with irregular schedules, shift workers, or anyone who finds strict timing difficult to maintain. You still take one injection per day, but the window for that injection is wider than with glargine or detemir.
Available Concentrations
Tresiba comes in two concentrations: U-100 (100 units per milliliter) and U-200 (200 units per milliliter). The U-200 version delivers the same dose in half the injection volume, which can make larger doses more comfortable. Both concentrations are available in prefilled pens, and the pen dials display the actual number of units regardless of concentration, so there’s no manual dose conversion needed.
Storage After Opening
One practical advantage of degludec is its in-use shelf life. Once you start using a Tresiba pen or vial, it stays stable at room temperature for up to 8 weeks. That’s notably longer than many other insulins, which typically need to be discarded after 28 days. For people who use smaller daily doses, this means less wasted insulin and fewer trips to the pharmacy.
Unopened pens and vials should be stored in the refrigerator until their expiration date, just like other insulin products.
Who Uses Insulin Degludec
Degludec is approved for adults and children with type 1 diabetes and for adults with type 2 diabetes. In type 1 diabetes, it serves as the background insulin and is paired with a rapid-acting insulin taken at meals. In type 2 diabetes, it may be used alone or alongside oral diabetes medications, and sometimes with mealtime insulin as well.
The people who tend to benefit most from switching to degludec are those who experience frequent nighttime lows on their current basal insulin, those who struggle with consistent injection timing, or those on high doses who prefer the smaller injection volume of the U-200 pen. It is not used for treating diabetic emergencies or for rapid blood sugar correction, since its onset is too gradual for that purpose.
Side Effects
The most common side effect of any basal insulin is hypoglycemia, and degludec is no exception. However, as the trial data shows, it carries a lower risk of nighttime lows compared to glargine. Other potential side effects include injection site reactions (redness, swelling, or itching), weight gain, and, rarely, allergic reactions. Because degludec builds up slowly and has a long duration, dose adjustments take several days to fully take effect. If your dose is changed, the new steady state won’t be reached for about three to four days.