Tresiba is not a GLP-1. It is a long-acting insulin, specifically a synthetic version of human insulin called insulin degludec. The confusion is understandable because both Tresiba and GLP-1 drugs are injectable medications used to manage blood sugar in type 2 diabetes, and they’re sometimes prescribed alongside each other. But they belong to entirely different drug classes and work in fundamentally different ways.
What Tresiba Actually Is
Tresiba is FDA-approved as a long-acting insulin analog for people aged 1 year and older with diabetes. Its active ingredient, insulin degludec, works like a slow-release version of the insulin your body would normally produce. After you inject it under the skin, the insulin molecules link together into long chains called multi-hexamers, forming a small depot that gradually releases insulin into your bloodstream over an extended period. This gives Tresiba a half-life longer than 25 hours, meaning it provides a steady, background level of insulin that lasts well beyond a full day.
Tresiba comes in pre-filled pens and is injected once daily. It’s approved for both type 1 and type 2 diabetes, which is a key distinction from GLP-1 medications.
How GLP-1 Drugs Work Differently
GLP-1 receptor agonists (brands like Ozempic, Trulicity, and Mounjaro) take a completely different approach to blood sugar control. Instead of delivering insulin directly, they mimic a gut hormone called GLP-1 that your body releases after eating. This hormone signals your pancreas to produce more insulin, but only when blood sugar is actually elevated. That “glucose-dependent” mechanism is a major safety advantage: GLP-1 drugs carry a lower risk of causing dangerously low blood sugar compared to insulin.
GLP-1 drugs also slow down how quickly food leaves your stomach and reduce the release of glucagon, a hormone that raises blood sugar. These extra effects contribute to weight loss, which is one reason GLP-1 medications have become so popular. By contrast, insulin therapy, including Tresiba, tends to cause modest weight gain.
Another important difference: GLP-1 drugs are only approved for type 2 diabetes (and in some cases, weight management). They rely on your pancreas still being able to produce insulin. People with type 1 diabetes, whose bodies make little or no insulin, need actual insulin like Tresiba to survive.
Why People Confuse Them
Several things blur the line between these two drug classes. Both are given as injections, often using similar-looking pen devices. Both are prescribed for type 2 diabetes. And to make things more confusing, there’s a combination product called Xultophy that contains both insulin degludec (the same insulin in Tresiba) and liraglutide (a GLP-1 receptor agonist). Each dose unit of Xultophy delivers 1 unit of insulin degludec plus 0.036 mg of liraglutide, up to a maximum of 50 units per day.
The existence of Xultophy highlights the fact that insulin and GLP-1 drugs complement each other rather than being interchangeable. Clinical trials of this combination found that patients lost about 0.7 kg on average, compared to a gain of 0.4 kg with insulin degludec alone. The GLP-1 component helps offset the weight gain that typically comes with insulin while also targeting post-meal blood sugar spikes that long-acting insulin doesn’t cover well.
Practical Differences at a Glance
- Drug class: Tresiba is a long-acting basal insulin. GLP-1 drugs are incretin mimetics.
- How they lower blood sugar: Tresiba delivers insulin directly. GLP-1 drugs stimulate your pancreas to release its own insulin when blood sugar rises.
- Hypoglycemia risk: Higher with Tresiba because it works regardless of blood sugar levels. Lower with GLP-1 drugs because their effect is glucose-dependent.
- Weight effects: Tresiba is associated with slight weight gain. GLP-1 drugs typically cause weight loss.
- Who can use them: Tresiba is approved for type 1 and type 2 diabetes. GLP-1 drugs are approved for type 2 diabetes only.
- Dosing frequency: Tresiba is injected once daily. GLP-1 drugs vary from twice daily to once weekly, depending on the specific medication.
Can You Take Both Together?
Yes, and it’s a common treatment strategy. Many people with type 2 diabetes use a long-acting insulin like Tresiba for steady background blood sugar control while taking a GLP-1 drug to manage post-meal spikes, reduce appetite, and limit weight gain. The two drug classes target different aspects of blood sugar regulation, so combining them can improve overall control while potentially reducing the total amount of insulin needed. This combination can be taken as two separate injections or as a single injection using a product like Xultophy.