How long does it take Zepbound (tirzepatide) to start working?

If you’re thinking about taking the weight loss medication Zepbound (tirzepatide), you’re probably eager to see it take effect quickly. But how long does it take for Zepboud to work? 

Like any medication, everyone responds a little differently, but you can expect it to take a few weeks (sometimes more) before you start seeing significant weight loss results from Zepbound. Let’s explore this more closely so you have a realistic idea of what may happen once you start the weight loss medication.

It takes about four weeks for Zepbound to reach steady levels in your body, which is when most people start to notice some modest weight loss. One of the major trials of tirzepatide (the active ingredient in Zepbound and Mounjaro) showed participants losing an average of 15% to 21% of their body weight over a period of  72 weeks, with more weight loss in those taking the highest dose of the drug. 

When you start Zepbound, your healthcare provider will initially prescribe a low starting dose, gradually increasing your dose over the next few weeks and months to minimize side effects while maximizing your weight loss on the medication. 

The speed at which you lose weight will depend on a range of factors, including your starting weight, your daily habit changes (including changes to your calorie intake and how much physical activity you get), and other factors like any underlying conditions you might have. 

One thing to be aware of is you should expect your weight loss to plateau at a certain point—that’s totally normal, and nothing to be concerned about. After all, if you kept losing weight indefinitely, you’d disappear! In studies, people who stayed on tirzepatide after initially losing over 20% of their body weight were able to continue losing an additional 5.5% over the next year. But those who stopped taking it regained 14% of the weight they had lost. So, staying on tirzepatide can help you keep the weight off and even shed a little more over time. 

Zepbound is part of a class of drugs you’ve probably heard of by now, called glucagon-like peptide-1 receptor agonists, or GLP-1s for short. These drugs work for weight loss in some key ways: 

• They slow down digestion, keeping food in the stomach for longer, which makes you feel fuller. 

• They send satiation signals to the parts of the brain that regulate our hunger hormones. 

For many people, the common side effects of GLP-1s—nausea, bloating, and other gastric symptoms—also tend to decrease appetite. In most cases, these side effects are mild to moderate and usually get better with time.  

Zepbound’s half life (the time it takes for the drug’s active concentration to reduce by half) is 5 days, but it can last in your system for up to 30 days. 

Zepbound is an injectable solution that comes in a vial or a prefilled  autoinjector pen that you’ll administer once a week at the dose your healthcare provider currently has you on. The drug peaks in your system within 8–72 hours, and by that one-week mark, its efficacy has mostly diminished. If you stop taking the medication, however, it’ll take another couple of weeks for it to be completely out of your system after your last dose. 

The average response to Zepbound is just that—an average. Which means you might respond a little differently than what’s shown in trials—and that could mean more or less dramatic results. Let’s take a look at some factors that could impact how quickly you respond to Zepbound.

Lifestyle interventions

We know that tirzepatide tends to work considerably better than even intensive lifestyle interventions alone, but the best combination is taking Zepbound while  making changes to your diet and physical activity levels. One review looked at how diet and exercise can help with weight loss on tirzepatide (and improve other health factors). This research suggests that with new anti-obesity medications like tirzepatide, the focus of lifestyle changes may shift from simply losing weight through calorie restriction to helping people adopt healthier lifestyles that improve body composition and overall well-being. 

If you thought Zepbound would get you off the hook for diet and exercise, unfortunately, it’s still important to take care of your health in these other ways. And doing so may make Zepbound work better and more quickly. 

Tolerance of side effects

When you start Zepbound, your healthcare provider will prescribe a low dose and increase it slowly over time. It generally takes up to five months to safely build up to the maintenance dose range. The higher the dose you’re on, the more weight you’re likely to lose, but you’re also much more likely to experience more side effects at higher doses. So, more doesn’t necessarily equal better. 

Everyone experiences and tolerates Zepbound side effects differently, and it’s important to pay attention to what your body is telling you (even if it means you may lose the weight a little slower). 

Health conditions

Certain health conditions make it harder to lose weight—namely, and somewhat ironically, type 2 diabetes (T2D). After all, tirzepatide was originally approved as a treatment for T2D. But we know that people with diabetes taking tirzepatide (and other GLP-1s) lose less weight on average than those without diabetes. Studies show people with diabetes have an average weight loss of around 15% of bodyweight compared to over 20% in those without diabetes.

Sex

When it comes to how well Zepbound works, women seem to fare better than men. In one study on weight loss results in people with diabetes, 62.5% of participants at the highest range of weight loss (over 15% of bodyweight) were women, while men made up the other 37.5%. We don’t know why this is exactly, but your sex assigned at birth might be a factor in how quickly you lose weight on Zepbound. 

Adherence

Staying consistent with your weekly Zepbound injections is pretty important for seeing the weight loss results you want to see. If you don’t take your medication consistently, it’s going to take Zepbound a lot longer to start working.

There are many reasons people may fall off the wagon, so to speak, with their medication adherence. Try setting a weekly alarm or using a medication reminder app, and sign up for automatic refills at your pharmacy to help prevent running out. Your healthcare provider can help guide you if you’re having trouble staying on schedule with Zepbound. 

Genetics

Some people respond better to Zepbound than others—and we don’t always know why. There are likely genetic factors that make some people more responsive to GLP-1s and weight loss interventions than others. Unfortunately, that’s not something you can change, but it’s important to be patient and follow your healthcare provider’s recommendations.  

Zepbound is a highly effective medication for weight loss, but results and timing of those results can vary. 

• You could start seeing modest weight loss within a couple of weeks of starting Zepbound, but it could take a few more weeks to see very significant results. 

• Most people continue losing weight steadily for a little over a year (16.5 months), at which point they generally hit an expected plateau. But studies show that staying on Zepbound can help you lose some additional weight, while stopping typically leads to substantial weight regain. 

• Some factors that can impact how long it takes Zepbound to work include lifestyle interventions, health conditions, your sex, adherence to the drug, and genetics. 

Learn more about Zepbound (tirzepatide) and whether it might be the right weight-loss medication for you. Ro’s Body program can offer you on-demand access to licensed healthcare providers who can help you get started on your weight loss journey and get access to life-changing medications such as Zepbound to help you keep the weight off, if appropriate for you.  

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

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Current version

January 30, 2025

Written by

Rachel Honeyman

Fact checked by

Patricia Weiser, PharmD

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About the medical reviewer

Patricia Weiser, PharmD

Patricia Weiser, PharmD, is a licensed pharmacist, health content writer, and medical reviewer with more than a decade of clinical experience in community and hospital pharmacy.