Tresiba is a long-acting insulin used to manage blood sugar in people with type 1 or type 2 diabetes. Its active ingredient, insulin degludec, provides a glucose-lowering effect that lasts at least 42 hours, making it one of the longest-acting basal insulins available. It’s approved for adults and children ages 1 and older.
How Tresiba Works
All basal insulins aim to provide a slow, steady background level of insulin throughout the day. Tresiba achieves this through an unusual molecular trick. In the pen, the insulin molecules are organized into small, paired clusters. Once injected under the skin, a preservative called phenol dissipates, and this triggers a dramatic structural change: the small clusters reorganize into long chains made up of hundreds of units. These chains form a soluble depot, a kind of slow-release reservoir sitting just beneath the skin.
From this depot, individual insulin molecules gradually separate and enter the bloodstream. The half-life at steady state is about 25 hours, which is considerably longer than older basal insulins. This slow, predictable release is what gives Tresiba its ultra-long duration and a relatively flat activity profile, meaning fewer peaks and valleys in blood sugar control over the course of a day.
Who Tresiba Is Prescribed For
Tresiba is FDA-approved for both type 1 and type 2 diabetes. In type 1, it serves as the background insulin in a basal-bolus regimen, paired with a rapid-acting insulin taken at meals. In type 2, it can be used alone or alongside other diabetes medications, including oral drugs or mealtime insulin, depending on how much insulin support a person needs.
The approval extends to pediatric patients as young as 1 year old. A 26-week clinical trial compared Tresiba to another long-acting insulin in children and adolescents (ages 1 to 17) with type 1 diabetes, and the results supported its use in that age group. It is not recommended for treating diabetic ketoacidosis, a serious complication that requires rapid-acting insulin and emergency care.
Dosing Flexibility
One of the practical advantages of Tresiba’s ultra-long action is dosing flexibility. Because its glucose-lowering effect extends well beyond 24 hours, the timing of your daily injection doesn’t need to be as rigid as with some other basal insulins. If you normally inject in the morning but are traveling or have an unpredictable schedule, you have a wider window to take your dose without a gap in coverage. That said, a minimum number of hours between doses should still be maintained, and your prescriber will give you specific guidance on this.
Tresiba is injected once daily under the skin of the thigh, upper arm, or abdomen. It comes in two concentrations: U-100 and U-200. Both are delivered via a prefilled pen, and the dose counter on each pen shows units of insulin regardless of concentration, so you don’t need to do any math when switching between the two.
Hypoglycemia Risk Compared to Other Basal Insulins
Low blood sugar, or hypoglycemia, is the most common concern with any insulin. A meta-analysis of seven clinical trials involving over 4,300 patients compared Tresiba to insulin glargine (the active ingredient in Lantus and Basaglar). Across all seven trials, Tresiba was associated with lower rates of nocturnal hypoglycemia, the kind that happens between midnight and 6 a.m. while you’re asleep. This difference reached statistical significance in three of the trials, regardless of whether patients had type 1 or type 2 diabetes.
Nighttime lows are particularly concerning because you may not wake up to recognize the symptoms. The flatter, more stable release profile of Tresiba helps explain why overnight dips occur less often. In a large real-world study of patients using Tresiba in routine clinical practice, confirmed hypoglycemia events were relatively uncommon: 84 episodes across 51 patients over a full year of follow-up, and serious adverse events were rare and unrelated to the drug.
Common Side Effects
The most frequently reported side effects are the ones common to all insulins. Low blood sugar tops the list, especially during the initial dose-adjustment period when you and your prescriber are finding the right amount. Injection site reactions, such as redness, swelling, or itching, can occur but tend to be mild and temporary. Weight gain is also possible, as it is with most insulin therapy. Rotating your injection sites helps reduce the risk of skin changes at any single spot.
Tresiba should not be used during an active episode of hypoglycemia or by anyone with a known allergy to insulin degludec or any of its inactive ingredients.
Storage and Handling
Before first use, Tresiba pens should be kept in the refrigerator. Once you start using a pen, or if an unopened pen has been left out, it stays good at room temperature (below 86°F) for 56 days. After eight weeks at room temperature, the pen should be thrown away even if insulin remains inside. Never freeze Tresiba, and keep it away from direct heat and sunlight. The pen cap should stay on when you’re not injecting to protect the insulin from light exposure.