Tirzepatide’s Mechanism of Action: How Does Tirzepatide Work?

Key takeaways:

Tirzepatide is a once-weekly injectable medication that’s available under two brand names: Mounjaro (for Type 2 diabetes) and Zepbound (for weight loss and obstructive sleep apnea, or OSA). Tirzepatide’s primary mechanism of action, or how it works, is mimicking two gut hormones.
Once injected, tirzepatide stimulates your pancreas to release insulin when you eat and lowers the amount of glucose (sugar) your liver makes. These actions help lower blood sugar for people with Type 2 diabetes.
Tirzepatide also slows the passage of food through the digestive tract and acts on areas of the brain that regulate appetite. It may also reduce food cravings. Together, these actions can contribute to weight loss.
Tirzepatide primarily treats OSA by helping you lose weight. But it may also help reduce inflammation that contributes to the condition.

Tirzepatide is a once-weekly injectable medication that’s available under two brand names: Mounjaro and Zepbound. Mounjaro is FDA approved to treat Type 2 diabetes in adults. Zepbound is approved for chronic weight management and obstructive sleep apnea (OSA) in certain adults.

Tirzepatide belongs to a medication class with a long name: dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist. It acts like GIP and GLP-1, two gut hormones that help regulate blood glucose (sugar), digestion, and appetite.

But what exactly happens in your body after you inject Mounjaro or Zepbound? Below, we break down tirzepatide’s mechanism of action and seven ways it works to manage diabetes, promote weight loss, and treat OSA.

1. Tirzepatide tells your pancreas to release insulin after you eat

One of the ways tirzepatide helps lower blood sugar is by encouraging your pancreas to release more insulin after you eat. Insulin helps move sugar from your bloodstream into your cells. By making more insulin available, tirzepatide helps lower blood sugar levels, especially post-meal sugar levels.

Since tirzepatide primarily promotes insulin release after you eat, it carries a lower risk of hypoglycemia (low blood sugar) than some diabetes medications, such as sulfonylureas. Sulfonylureas, such as glipizide (Glucotrol XL), stimulate insulin release regardless of whether you ate.

2. Tirzepatide lowers the amount of new sugar your liver makes

Tirzepatide also lowers the amount of glucagon, a hormone released by the pancreas that tells the liver to make sugar. As a result, the liver produces less sugar. And this helps lower blood sugar levels for people living with Type 2 diabetes.

3. Tirzepatide slows the movement of food out of your stomach

It’s common to feel fuller than usual after meals while taking tirzepatide because it slows gastric emptying — how quickly food moves from your stomach to your intestines. This action is beneficial for both Type 2 diabetes and weight loss. But it’s also thought to contribute to many of tirzepatide’s digestion-related side effects, such as nausea and constipation.

Slowed or delayed gastric emptying reduces how quickly your body absorbs carbohydrates from food. This can help balance sugar levels after you eat. And it can make you feel fuller for longer, causing you to eat less and lose weight over time.

For some people, tirzepatide’s impact on gastric emptying may only be temporary. Generally, this effect is most noticeable shortly after starting treatment. But people taking the highest Mounjaro dosage or Zepbound dosage (15 mg per week) may continue to experience the sensation of feeling fuller.

EXPERT PICKS: WHAT TO READ NEXT

Compare tirzepatide injections: See what experts say about the similarities and differences between Mounjaro and Zepbound, two brand-name versions of tirzepatide.
What taking Mounjaro feels like: Real people share their experiences with Mounjaro, a medication that’s proven effective at treating Type 2 diabetes.
Possible side effects: Read about tirzepatide’s potential side effects — from diarrhea to hair loss — and how to manage them.

4. Tirzepatide targets areas in your brain that regulate appetite

In addition to its effects in the digestive tract, tirzepatide also affects the brain. There are receptors (chemical binding sites) for GIP and GLP-1 in areas of the brain that regulate your appetite. Once injected, tirzepatide attaches to these receptors, which can help lower your appetite. This can cause you to eat less and lose weight over time.

Good to know: While a smaller appetite is normal with tirzepatide, having no appetite isn’t. You should still be eating regular meals, preferably following a dietary plan decided on by you and your prescriber. If you find you have no appetite at all, let your prescriber know.

5. Tirzepatide may reduce cravings for certain foods

Tirzepatide’s activity in the brain may also reduce food cravings. So don’t be surprised if you no longer want to eat certain foods or snacks. Some people also report they have a lower desire to consume alcohol.

When you take a medication that mimics GLP-1, such as tirzepatide, it interferes with dopamine signaling in the brain. Dopamine is a chemical involved in the brain’s reward system. When you eat food you enjoy, your brain releases dopamine and makes you want to eat it again. This can result in food cravings.

6. Tirzepatide may counteract certain hunger hormones that affect weight gain

Tirzepatide may counteract certain hormones that contribute to weight gain.

Ghrelin and leptin are two hormones that help tell you when you’re hungry or full. But they work in somewhat opposite ways, as detailed in the table below.

	Ghrelin (the “hunger” hormone)	Leptin (the “I’m full” hormone)
How it works	Tells your brain it’s time to eat and your body to store fat Produced mainly by the stomach Signals your pancreas to release glucagon May lower the amount of insulin released by the pancreas Speeds up gastric emptying	Tells your brain to eat less over the long term as your body creates more fat cells Released from fat cells Slows gastric emptying

When you eat fewer calories, ghrelin levels rise and leptin levels fall. These changes make you feel hungrier and can cause you to eat more. This is one reason it can be difficult to maintain weight loss long term.

But tirzepatide may fight against these shifting hormone levels. Experts think this may be one reason why tirzepatide can help people maintain weight loss. But keep in mind that this effect only lasts for as long as you’re taking the medication. If you stop treatment, you may regain some of the weight you lost.

7. Tirzepatide might lower inflammation that plays a role in OSA

Tirzepatide is mainly thought to treat OSA by helping you lose weight. Weight loss is one of several recommended goals to help people manage the condition and reduce symptoms. But it’s likely that tirzepatide works in other ways to treat OSA.

Tirzepatide may also help lower levels of certain inflammatory chemicals in the body. In particular, it may reduce levels of chemicals that play a role in OSA.

Tirzepatide’s ability to promote insulin release might help with OSA, too. High blood sugar levels can promote inflammation throughout the body. By raising your natural insulin levels, tirzepatide helps lower sugar levels. Over time, this can help reduce inflammation, which may be contributing to OSA.

Frequently asked questions

Tirzepatide and Ozempic (semaglutide) both act like the gut hormone GLP-1. But tirzepatide also acts like another hormone: GIP. This difference may help tirzepatide lower sugar levels more and promote greater weight loss. Tirzepatide is also FDA approved for OSA, which Ozempic isn’t. But Ozempic is approved to lower serious cardiovascular and kidney disease-related problems for certain people, which tirzepatide isn’t.

Tirzepatide is safe for most people when used as directed. But it can cause side effects. Common tirzepatide side effects are digestive related and include nausea, diarrhea, and constipation. These side effects usually improve or go away as your body adjusts to the medication.

Serious tirzepatide side effects are rare, but they may include gallbladder issues and low blood sugar. Animal studies have also noted that tirzepatide may raise the risk for certain thyroid tumors. But this side effect hasn’t been reported in human studies.

The bottom line

Tirzepatide (Mounjaro, Zepbound) is an once-weekly injection used for Type 2 diabetes, chronic weight management, and obstructive sleep apnea (OSA) in adults. Tirzepatide’s main mechanism of action (how it works) is mimicking two gut hormones that regulate blood glucose (sugar), digestion, and appetite.

Tirzepatide helps treat Type 2 diabetes by telling the pancreas to release more insulin and the liver to make less sugar. Tirzepatide helps with weight loss by targeting areas of the brain that regulate appetite and food cravings, as well as counteracting certain hunger hormone changes. It also slows the movement of food through the digestive tract, which can be beneficial for both diabetes and weight loss.

Tirzepatide works for OSA mainly through its ability to promote weight loss. But it may also help lower inflammation that plays a role in the condition.

Tirzepatide’s effects only last for as long as you take the medication. Long-term use may be necessary for continued diabetes, weight loss, or OSA benefits.

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Written by:

Kristina D. Carter, PharmD, MBA, MHA

Kristina D. Carter, PharmD, MBA, MHA, has over 25 years of experience working in healthcare. She is registered as a licensed pharmacist in Georgia, Indiana, and Tennessee.

Edited by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

Reviewed by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

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