How does tirzepatide work? Mounjaro and Zepbound explained

Key Points

• Tirzepatide mimics two natural hormones in your body that help control blood sugar levels, lower your appetite, and slow down digestion
• It's available under FDA-approved brands Mounjaro for type 2 diabetes, and Zepbound for weight loss
• Tirzepatide can lower A1C levels in people with type 2 diabetes within 8-12 weeks and lead to an average 15-20% weight reduction over 72 weeks

Tirzepatide is a medication that mimics two natural hormones in the body that help control blood sugar and appetite. Eli Lilly sells it under two different brand names: Mounjaro for type 2 diabetes and Zepbound for chronic weight management.

If you're planning to take tirzepatide, understanding how it works can help you make an informed decision about your health journey.

How tirzepatide works

Sarah Logan, Registered Dietitian, RD, explains, "Tirzepatide acts like an assistant for your body in the weight loss process to help manage hunger and lower blood sugar."

In other words, tirzepatide is a copycat. It imitates two natural hormones in your body, GLP-1 and GIP, that control blood sugar, appetite, and insulin release after you eat.

Tirzepatide benefits include:

• Blood sugar control
• Weight loss
• Reduced appetite
• Less glucose is stored and released from the liver

1. Lowers blood sugar after a meal

The hormone insulin is supposed to work like an efficient traffic controller. It’s job is to direct glucose "vehicles" to your brain, lungs, heart, and other organs and muscles after meals. Any excess is stored in short-term parking as glycogen in the liver or long-term as fat in fat cells.

However, this system does not work well for people with type 2 diabetes. Insulin may appear on the scene, but without the power it has in people without diabetes. Cells may begin to ignore insulin’s signals and refuse to absorb glucose, leading to a dangerous glucose traffic jam in the bloodstream.

When this happens, your body may release more insulin, but if cells do not respond, your blood sugar may remain high, and more fat may be stored there. At the same time, your body also stops burning fat efficiently, leading to weight gain.

Here’s when tirzepatide comes to the rescue. It gets activated when you eat, triggers insulin release, and improves how cells respond to insulin’s effects.

This clears glucose traffic in the blood more efficiently and prevents dangerous jams (blood sugar spikes).

2. Weight loss

Tirzepatide slows down digestion, helping you feel full faster and with less food. It does this by simulating GLP-1, a hormone called incretin, which is released when we eat, triggers insulin production, and makes food move more slowly through your digestive system.

3. Reduces cravings

When people start taking tirzepatide, they are often pleasantly surprised that the volume on their “food noise,” constant cravings for food, gets turned all the way down. It’s because tirzepatide signals the area in the brain responsible for appetite, telling it that you’re full. This way, you end up eating less and lose weight.

4. Less glucose is stored and released from the liver

Tirzepatide prevents your liver from dumping extra sugar into your bloodstream when you don't need it. It also stops the liver from storing more glucose when you eat, which helps control blood sugar levels.

Yes, the liver produces glucose. It does it by breaking down sugar stored in the liver (glycogen) and making glucose from non-carbohydrate sources during fasting.

To lose weight and control blood sugar on tirzepatide, the dose also matters.

Tirzepatide dosage

Mounjaro dosage

Mounjaro (tirzepatide for type 2 diabetes) comes in six different doses: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg. The medication comes in pre-filled, single-dose pens for injection under the skin, taken once weekly.

Treatment typically begins with 2.5 mg once weekly for four weeks. This lower starting dose helps your body adjust while minimizing side effects. After this period, your healthcare provider will likely increase your dose gradually at 4-week intervals. They'll adjust until reaching the right therapeutic dose based on your response and glucose targets.

The recommended maintenance doses range from 5 mg to 15 mg once weekly. Your doctor will adjust based on your specific needs and tolerance.

Zepbound dosage

Zepbound (tirzepatide for weight management) follows a similar strategy with the same strength options: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg. It's also injected under the skin once weekly.

For weight management, you typically start with 2.5 mg once weekly for the first four weeks. This initial dose helps your body adapt to the medication.

After this introduction, your healthcare provider will gradually increase the dose. They typically add 2.5 mg every 4 weeks until reaching a target maintenance dose. The maximum recommended dose for weight management is 15 mg once weekly.

Tirzepatide benefits

Mounjaro results for type 2 diabetes

Clinical trials measured how tirzepatide affects blood sugar levels in people with type 2 diabetes. Studies found that most people reach the target A1C levels below 7% in about 8 weeks. A1C levels of 6.5% or lower were typically achieved within about 12 weeks of starting treatment.

Mounjaro users also saw other diabetes-related health benefits. These included better insulin sensitivity, lower fasting glucose levels, and weight reduction.  Additionally, weight loss is an important benefit for many people with type 2 diabetes.

Zepbound weight loss results

Clinical studies of Zepbound for weight management have documented weight changes over time. These studies measured weight reduction over a 72-week period (about a year and a half).

Clinical trials show that weight loss on tirzepatide is related to dosage:

• 5 mg dose: average weight loss of about 15%
• 10 mg dose: average weight loss of about 20%
• 15 mg dose: average weight loss of 20.9%

Please note that individual results may vary. Zepbound and Mounjaro are only available through a prescription from a healthcare provider who will evaluate dosage based on your health.

How long does it take for tirzepatide to work?

How long does Mounjaro take to work?

Tirzepatide (Mounjaro) begins affecting your body right after you receive your shot. Most people don't notice changes right away. It usually takes several weeks before you see measurable improvements. Studies show that blood sugar levels (A1c) typically start dropping around the four-week mark after beginning treatment.

How long does Zepbound take to work?

Based on clinical studies, Zepbound typically takes about a year and a half (72 weeks) for most people to achieve 15-20% weight loss.

While you may notice some weight loss sooner, the significant results seen in studies may take a few months. Everyone responds differently, and your healthcare provider can help set realistic expectations for your individual situation.

Optimizing tirzepatide results: Diet and lifestyle factors

Tirzepatide works best as part of a complete approach to metabolic health. Even in clinical trials, people who lost weight on tirzepatide followed a calorie-deficient diet and exercised daily.

"Diet is crucial to someone's success on tirzepatide because even with great medication, our food intake ultimately determines the result of our weight loss and drives our metabolism. A diet high in protein, anti-inflammatory whole foods, and low in sugar and processed foods is only going to amplify someone's weight loss results and help you maintain your results once the goal weight is achieved," explains Logan, RD.

For best results, consider:

• Following a balanced diet focused on whole foods, lean proteins, and smaller amounts of healthy fats and complex carbs
• Practicing portion control, which becomes easier as tirzepatide reduces appetite
• Getting enough nutrition, even with a reduced appetite
• Doing regular physical activity, including both cardio and strength training
• Staying well hydrated
• Getting quality sleep
• Managing stress through mindfulness practices

A registered weight loss dietitian who specializes in weight management can help you manage your diet on tirzepatide.

They can provide personalized diet recommendations that work with tirzepatide's effects. They help you navigate food sensitivites, allergies, and preferences. They also help you get the nutrition you need, even if you’re battling side effects or do not feel hungry.

A dietitian can also help you develop sustainable eating patterns that support long-term success. They address behavioral aspects of eating that medication alone can't change.

Final thoughts: How does tirzepatide work?

Tirzepatide is available as Mounjaro for type 2 diabetes and Zepbound for weight management.

Tirzepatide simulates two hormones in the body that simultaneously target multiple metabolic pathways. It slows down digestion, tells the pancreas to release insulin, and prevents the liver from making and storing too much glucose. At the same time, it tells the appetite center in the brain that you’re full faster, so you end up eating less food.

Individual responses vary. You should maintain realistic expectations while working closely with healthcare providers throughout their treatment.

Find a GLP-1 registered dietitian covered by your insurance.

Frequently Asked Questions (FAQs)

1. Are Ozempic and tirzepatide the same?

Although they treat similar health conditions, Ozempic (semaglutide) and tirzepatide are different medications. Ozempic mimics one type of hormone, called GLP-1, while tirzepatide is a dual-action medication that simulates GLP-1 and GIP, a chemical that boosts the action of GLP-1.

2. How does tirzepatide work for weight loss?

Tirzepatide promotes weight loss by decreasing appetite by acting on brain centers that control hunger. It slows stomach emptying to extend feelings of fullness and reduces food cravings. These combined effects lead to eating fewer calories and better energy metabolism. This results in significant weight reduction when used with lifestyle changes.

3. What qualifies you for tirzepatide?

To qualify for tirzepatide in the United States, you must meet specific medical criteria that depend on the medication’s approved use. For type 2 diabetes, tirzepatide (Mounjaro) is prescribed to adults with obesity to help lower blood sugar, alongside diet and exercise.

For weight management, tirzepatide (Zepbound) is approved for adults with a body mass index (BMI) of 30 or higher (classified as obesity), or a BMI of 27 or higher if they also have at least one weight-related health condition, such as high blood pressure, type 2 diabetes, or high cholesterol.

Your healthcare provider will review your medical history, current health, and previous weight management efforts to determine if tirzepatide is appropriate for you.

Remember that even if your doctor prescribes tirzepatide, your insurance company must also approve coverage. Insurance companies have their own rules and may require documentation, such as proof of your diagnosis, BMI, and previous treatments you’ve tried.

4. What are the drawbacks of tirzepatide?

Like any medication, tirzepatide may cause side effects. The most common side effects of tirzepatide are gastrointestinal issues such as nausea, vomiting, diarrhea, constipation, stomach discomfort, burping, or gas. Additional side effects include decreased appetite, injection site reactions, fatigue or weakness, heartburn or acid reflux, burping or gas, headaches, and dizziness.

Other potential drawbacks include having to take weekly injections, a high cost without insurance, possible insurance coverage issues, potential weight gain if stopped, and risk of more serious side effects in some people.

Less common but more serious potential side effects requiring medical attention include:

• Pancreatitis (inflammation of the pancreas)
• Hypoglycemia (low blood sugar), particularly when used with other diabetes medications
• Allergic reactions
• Potential thyroid issues (including thyroid C-cell tumors in animal studies)
• Kidney problems
• Gallbladder issues

Always tell your healthcare provider about any side effects you experience. Your provider may recommend adjustments if side effects persist or become severe. Never stop taking tirzepatide or adjust your dose on your own. Doing so without medical supervision could cause rapid blood sugar changes for people with diabetes or weight regain for those using it for weight management.

Get a personalized tirzepatide diet plan from a weight loss dietitian who accepts your insurance.

The views expressed by authors and contributors of such content are not endorsed or approved by Fay and are intended for informational purposes only. The content is reviewed by Fay only to confirm educational value and audience interest. You are encouraged to discuss any questions that you may have about your health with a healthcare provider.