Yes, Tresiba (insulin degludec) is a long-acting insulin. It’s actually classified as “ultra-long-acting” because its glucose-lowering effect lasts at least 42 hours after a single injection, making it one of the longest-duration basal insulins available. Its half-life at steady state is approximately 25 hours, regardless of dose.
How Tresiba Works in Your Body
What makes Tresiba last so long comes down to how it behaves after injection. In the pen, the insulin exists as pairs of hexamers (clusters of six insulin molecules joined together). Once injected under the skin, these pairs link up into long, filament-like chains of many hexamers. These chains stay soluble but are far too large to be absorbed quickly into the bloodstream.
Over time, zinc gradually leaves these chains, causing them to slowly break apart and release individual insulin molecules. Because absorption speed is closely tied to molecular size, this process creates a slow, steady trickle of insulin into circulation rather than a surge. That steady release is what gives Tresiba its flat, predictable blood-sugar-lowering profile throughout the day.
How Long the Effect Lasts
In clinical testing, Tresiba’s glucose-lowering effect persisted for at least 42 hours after the last dose in a series of eight daily injections. That’s roughly 18 hours longer than a standard 24-hour basal insulin. The 25-hour half-life means that even when your next dose arrives, a meaningful amount of the previous dose is still active. This overlap creates a smooth, stable background insulin level once you’ve been taking it for a few days.
Steady-state concentration, the point where blood levels of the drug become consistent from day to day, is reached within two to three days of once-daily dosing. This was consistent across people with type 1 and type 2 diabetes, including elderly patients and African American and Hispanic/Latino subjects.
Dosing Flexibility
Because Tresiba’s action extends well beyond 24 hours, it offers more flexibility than most basal insulins if your schedule varies. The long duration means that if you occasionally take your dose a few hours earlier or later than usual, you’re less likely to experience a gap in coverage or a dangerous overlap. That said, a consistent daily schedule still produces the most predictable results.
Available Concentrations
Tresiba comes in two strengths: U-100 (100 units per milliliter) and U-200 (200 units per milliliter). Both deliver the same insulin molecule at the same duration of action. The difference is volume. The U-200 pen allows doses up to 160 units in a single injection, which is useful for people who need larger daily doses. Because U-200 packs twice the insulin into the same volume of liquid, the injection itself is half the size, which can make high-dose shots more comfortable.
Both concentrations come in prefilled FlexTouch pens. The dose counter on each pen shows units of insulin (not volume), so switching between the two doesn’t require any math on your part.
Storage After Opening
One practical advantage of Tresiba over some other insulins is its shelf life after first use. An opened Tresiba pen stays stable at room temperature (up to 86°F or 30°C) for eight weeks. Many other insulin pens need to be discarded after 28 days. That extra month of usable life reduces waste, especially for people on lower daily doses who take longer to finish a pen.
How Tresiba Compares to Other Basal Insulins
Most basal insulins fall into two broad categories. Older long-acting options like insulin glargine (Lantus) and insulin detemir (Levemir) have durations of roughly 18 to 24 hours, which is why some people need to take them twice daily. Tresiba’s 42-plus-hour duration puts it in the ultra-long-acting category, making twice-daily dosing unnecessary. Its flatter activity profile also means fewer peaks and valleys in blood sugar throughout the day, which can translate to a lower risk of low blood sugar episodes, particularly overnight.
The tradeoff is that because Tresiba builds up in your system over days, dose adjustments take longer to fully take effect. If your dose needs to change, you won’t see the complete impact of the new dose for two to three days.