How does Zepbound work for weight loss?

Zepbound (tirzepatide) is a once-weekly injectable prescription medication approved by the US Food and Drug Administration (FDA) for chronic weight management and obstructive sleep apnea (OSA). Zepbound works by mimicking two natural gut hormones, GLP-1 and GIP, which may help people feel full faster and curb cravings.

Clinical trials show that Zepbound may lead to an average weight loss of up to 20.9% in 72 weeks.

Read on for more details about how Zepbound works, including who it is right for, how long to take it, and what side effects to expect.

Zepbound works for weight loss by:

• Keeping food in the stomach longer, so people feel full sooner and longer

• Sending satiety signals to the brain that regulate appetite, reducing hunger and calorie consumption

• Quieting "food noise" (intrusive, recurring thoughts about food) so people feel less preoccupied with eating

• Helping manage insulin and glucose levels to avoid blood sugar spikes and crashes

“Zepbound works by mimicking the GLP-1 hormone in the body in order to regulate blood sugar, slow down digestion, and signal fullness to the brain,” says Paul Rosenberg, MD, a board-certified plastic surgeon at the New Jersey Gynecomastia Center. “This helps reduce appetite and keep people feeling full for longer after eating, which in turn supports weight loss."

Dr. Rosenberg adds that Zepbound may also improve insulin sensitivity, making it potentially beneficial for people with insulin resistance or prediabetes.

Zepbound is a dual GIP/GLP-1 receptor agonist, meaning it targets two receptors in the body instead of just one. It works on both GLP-1 (glucagon-like peptide 1) and GIP (glucose-dependent insulinotropic polypeptide). This may help explain why tirzepatide (the active ingredient in Zepbound) is more effective at both weight loss and blood sugar control than placebo and single-receptor GLP-1 medications such as Wegovy (semaglutide), Ozempic (semaglutide), or Saxenda (liraglutide).

Both GIP and GLP-1 are gut hormones that the body naturally produces. After eating, these hormones direct the pancreas to release more insulin and tell the liver to slow down glucose production. This helps balance blood sugar levels. At the same time, these hormones slow down how quickly food moves through the stomach into the small intestine (a process known as gastric emptying) and send signals to the brain signaling fullness.

Research suggests their role in appetite regulation may go even further, by reducing cravings and quieting "food noise,” such as when and what to eat next.

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Zepbound works very well for weight loss. In a 72-week clinical trial of people with obesity or overweight, those who took Zepbound lost between 15%–20.9% of their body weight, while the placebo group lost 3.1%.

More than one-third of participants on the highest 15 mg dose of Zepbound lost at least 25% of their body weight. In addition to the medication, participants received counseling sessions to improve their eating habits (by consuming 500 fewer calories per day) and increase their physical activity to at least 150 minutes per week.

Part of what makes Zepbound so effective is that it tackles weight loss from multiple angles.  

"These drugs work in two different ways to reduce how much we eat vs. earlier generation medications, which either cut down cravings or reduced food intake," says Peminda K. Cabandugama, MD, a board-certified endocrinologist and clinical associate professor of medicine at the Cleveland Clinic Lerner College of Medicine of Case Western University.

Targeting hormones to produce significant weight reduction is why Zepbound and Wegovy are sometimes referred to as"second generation" weight loss medications. Zepbound is meant to be used in combination with a reduced-calorie eating plan and regular physical activity.

Zepbound starts working once it is injected, but it will take about four weeks to reach a steady concentration in the bloodstream. People typically start to notice weight loss at this point, with those in clinical trials experiencing around 4% weight loss within the first month. The majority of weight loss occurs in the first nine months, although people may continue to lose weight if they continue taking the medication.

While some weight loss may occur in the first four weeks, it typically takes longer to experience the full effects of the medication. In part, this is due to the gradual dosing schedule.

Zepbound follows a titration schedule, where the dosage is gradually increased over a period of weeks to months until an effective and tolerable dose is identified — one at which a person experiences the therapeutic benefits while managing any side effects. Once that dose is reached, it becomes the maintenance dose. For Zepbound, maintenance doses are 5 mg, 10 mg, or 15 mg weekly.

Here is an overview of Zepbound dosages: 

What factors affect how long it takes Zepbound to work?

Several factors influence how quickly — and how much — a person responds to Zepbound, including starting weight, eating habits, activity level, and dose, including:

• Starting weight: People with a higher starting weight may see more dramatic early results — at least in terms of overall pounds — as the percentage of body weight lost tends to be similar across groups.

• Diabetes: People with type 2 diabetes tend to experience somewhat smaller weight loss compared with those without.

• Dose: Zepbound starts at a low dose and increases gradually over several months with guidance from a healthcare provider. The full titration schedule spans 20 weeks, and the most noticeable results are typically seen at a higher dose.

• Eating habits and activity level: Following a reduced-calorie eating plan and getting at least 150 minutes of physical activity per week may help accelerate progress.

• Individual response: Research suggests that some people are "late responders," meaning they experience less than a 5% weight reduction by week 12.

"Most people continue to take Zepbound as long as it is effective and they can tolerate the side effects," says Dr. Rosenberg. "Stopping Zepbound without incorporating significant lifestyle changes often leads to the return of appetite and weight gain."

In one study of Zepbound, participants took the two highest maintenance doses for 36 weeks and lost an average of 20.9% of their body weight. Some participants were then switched to a placebo while others continued taking Zepbound. Over the next year, those switched to a placebo regained 14% of their body weight, while those continuing Zepbound lost an additional 5.5%.

“Weight is a set point,” says Dr. Cabandugama. “What we are doing [with these medications] is bringing that set point down. The weight can still go back up. The mindset we want people to think about with obesity is a chronic disease.” He uses the example of high blood pressure: if blood pressure is controlled, patients would not stop their medication; they keep taking it to maintain that control. "If you think of obesity as a chronic disease, it is the same thing: you want to manage it," Dr. Cabandugama says.

Zepbound has a half-life of 5 days. A medication's half-life describes the length of time it takes for the body to eliminate half of it. Thanks to Zepbound's multi-day half-life, it only needs to be injected once a week.

Because Zepbound has a relatively long half-life, it also takes longer to clear from the body fully. Once Zepbound is discontinued, it takes about 30 days to be completely eliminated, according to Eli Lilly, the maker of Zepbound.

Zepbound is FDA-approved for weight loss and weight management in adults with:

• Obesity

• Overweight with a weight-related comorbidity, such as type 2 diabetes, high blood pressure, high cholesterol, heart disease, or sleep apnea

In addition, as of December 20, 2024, the FDA approved Zepbound for a second purpose: to treat obstructive sleep apnea (OSA) in adults with obesity.  

“A good candidate for Zepbound is typically an adult with a BMI of 30+ or someone with a BMI of 27+ who also has weight-related health issues like high blood pressure, type 2 diabetes, or sleep apnea,” says Dr. Rosenberg. “Good candidates are also those who are ready to commit to lifestyle changes, like a nutrient-rich, balanced diet and regular exercise, as Zepbound is most effective when used in combination with these healthy lifestyle changes.”

“Weight loss is not just about hitting a number, but also improving quality of life,” says Dr. Cabandugama. “Everyone [who is a candidate for Zepbound] has the same comorbidity, which is the reduced quality of life you have with obesity.”

Who should avoid Zepbound? 

Like most prescription medications, Zepbound is not safe for everyone, and some people should not take it. "Anyone who has had, or has a family history of, medullary thyroid cancer or multiple endocrine neoplasia syndrome type 2 is advised against taking Zepbound," says Dr. Rosenberg. "Those with a known hypersensitivity to GLP-1 receptor agonists would also not be good candidates for Zepbound or any other GLP-1 receptor agonist."

Besides these contraindications, some people may be more likely to experience serious side effects on Zepbound, including those with:

• Severe gastrointestinal disease

• Kidney or gallbladder problems

• A history of diabetic retinopathy (a vision-related complication of type 2 diabetes)

People who are pregnant, trying to become pregnant, or planning surgery should inform their healthcare provider before starting Zepbound. Zepbound may also interact with insulin, insulin secretagogues, and oral contraceptives (birth control pills), so sharing a complete list of current medications with a healthcare provider before starting Zepbound is important. A healthcare provider can advise on dosage adjustments or recommend another weight loss medication if needed.

“The most common side effects of Zepbound are nausea, vomiting, diarrhea, constipation, and GI discomfort,” says Dr. Rosenberg. “These side effects typically improve as your body adjusts to the medication.”

The following are the most common Zepbound side effects reported in clinical trials for weight loss:

While rare, Zepbound can cause serious side effects. These include:

• Severe gastrointestinal reactions

• Acute kidney injury

• Acute gallbladder disease

• Acute pancreatitis

• Serious allergic reactions

• Hypoglycemia (low blood sugar)

• Diabetic retinopathy complications

• Depression and suicidal behavior or ideation

• Pulmonary aspiration during general anesthesia or deep sedation

How to manage Zepbound side effects 

Zepbound does have a long list of potential side effects, but the good news is that the most common ones, like nausea and vomiting, tend to lessen with time as your body gets used to the medication. If you’re experiencing gastrointestinal side effects on Zepbound, there are things you can do to manage them. 

“To manage side effects, it helps to eat smaller, more frequent meals and avoid large, high-fat, or greasy meals,” Dr. Rosenberg says. “Staying hydrated and eating bland, low-acid foods like crackers, rice, or bananas can also reduce nausea.” He adds that if side effects persist or worsen, patients should talk with their healthcare provider about adjusting the dosage or the timing of the doses. And if the side effects are intolerable, it’s a good idea to explore other, more sustainable weight loss options.

Other tips for managing Zepbound side effects include:

• Avoiding alcohol and carbonated beverages

• Eating slowly and stopping once reaching a  feeling of fullness

• Not lying down after eating

• Eating a balanced diet that includes adequate fiber

• Increasing physical activity

• Asking a healthcare provider about anti-nausea medication, stool softeners, or probiotics

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Here is a summary of what to know about how Zepbound works, what to expect when taking it, and how to get the most out of it.

• Zepbound works by mimicking two gut hormones — GLP-1 and GIP — that slow gastric emptying, signal fullness to the brain, and help manage blood sugar levels.

• Tirzepatide, the active ingredient in Zepbound, targets both GLP-1 and GIP receptors. Research suggests this dual action may make it more effective at reducing appetite and managing body weight compared with single-receptor GLP-1 medications.

• Zepbound starts working upon injection, but it may take about a month before weight loss is noticeable — around 4% of body weight, on average, in clinical trials.

• Zepbound may cause a number of side effects, many of which are digestive in nature and tend to resolve with time as the body adjusts to the medication.

• Zepbound works best when combined with a reduced-calorie eating plan and regular physical activity. Stopping the medication may lead to weight regain, especially if these lifestyle changes are not maintained.