Insulin Degludec works by forming a slow-release depot under your skin that steadily delivers insulin into your bloodstream for over 42 hours, keeping your blood sugar stable around the clock.

What Insulin Degludec Does in Your Body

To understand how Insulin Degludec (Tresiba) works, it helps to think of it like a time-release capsule — except instead of a pill dissolving in your stomach, it's an insulin depot dissolving slowly under your skin.

Here's what happens step by step:

Step 1: You Inject It

When you inject Tresiba under your skin (into your thigh, upper arm, or abdomen), the insulin molecules do something unusual. They link together into long chains called multi-hexamers. Think of it like pearls on a string — the insulin molecules connect end to end and form a stable reservoir right at the injection site.

Step 2: The Depot Slowly Breaks Apart

Over the next day and a half (and beyond), these chains gradually break down. Individual insulin molecules — called monomers — slowly detach from the ends of the chains and enter your bloodstream. This happens at a very steady, predictable rate.

This is what makes Insulin Degludec "ultra-long-acting." Unlike faster insulins that flood your system quickly, Tresiba trickles in over 42+ hours.

Step 3: Insulin Does Its Job

Once in your blood, the insulin monomers work the same way your body's natural insulin does:

• They bind to insulin receptors on your muscle and fat cells
• This signals those cells to open up and absorb glucose (sugar) from your blood
• At the same time, insulin tells your liver to stop producing extra glucose

The result: your blood sugar stays in a more normal range, without the dramatic spikes and crashes that come with shorter-acting insulins.

How Long Does It Take to Work?

Insulin Degludec doesn't have a sharp "peak" like mealtime insulins. After injection, it begins working within about 1 hour, but because the release is so gradual, it reaches a steady state after 2–3 days of daily dosing. This means the full effect builds up over the first few days of use.

This is important to know: don't expect dramatic results on day one. Your doctor will have you titrate (gradually adjust) your dose over days to weeks.

How Long Does It Last?

This is where Insulin Degludec really stands out. Each dose lasts more than 42 hours — significantly longer than other basal insulins:

• Insulin Degludec (Tresiba): 42+ hours
• Insulin Glargine (Lantus, Basaglar): ~24 hours
• Insulin Detemir (Levemir): ~12–24 hours
• Insulin Glargine U-300 (Toujeo): ~36 hours

The 42+ hour duration gives you a built-in buffer. If you're a few hours late with your dose, you still have insulin working in your system. That's why Tresiba allows flexible dosing — you can inject at any time of day, as long as there are at least 8 hours between doses.

What Makes Insulin Degludec Different from Similar Medications?

Several basal insulins are on the market, so what sets Insulin Degludec apart?

Flatter Profile

Insulin Degludec has the flattest glucose-lowering profile of any basal insulin. This means less variability from day to day — your blood sugar stays more consistent. Clinical studies showed significantly lower peak-to-trough fluctuation compared to Insulin Glargine.

Flexible Timing

Unlike Insulin Glargine, which ideally should be taken at the same time every day, Tresiba's ultra-long duration allows flexible dosing times. This is a real advantage for people with irregular schedules — shift workers, travelers, or anyone who sometimes forgets a dose.

Lower Hypoglycemia Risk

The flat, steady release means fewer episodes of nocturnal hypoglycemia (overnight low blood sugar) compared to some other basal insulins. In the DEVOTE trial, Insulin Degludec showed a significant reduction in severe hypoglycemia compared to Insulin Glargine in type 2 diabetes patients at high cardiovascular risk.

Two Concentrations

Tresiba comes in U-100 and U-200. The U-200 pen delivers the same dose in half the injection volume, which is more comfortable for patients who need higher doses. Both deliver the same amount of insulin per unit — the pen dials adjust automatically.

No Generic Yet

One downside: there's no generic or biosimilar Insulin Degludec as of 2026. That makes cost a factor — though savings programs can help significantly.

For comparison with other options, see our guide to Insulin Degludec alternatives.

Final Thoughts

Insulin Degludec's unique multi-hexamer depot mechanism gives it the longest duration of any basal insulin on the market. For patients, that translates to more stable blood sugars, flexible dosing, and fewer low blood sugar episodes — especially overnight.

If you're looking to fill a Tresiba prescription, Medfinder can help you find it in stock at a pharmacy near you.