Mounjaro: A week by week weight loss guide

What is it like taking Mounjaro? Our weekly guide shines a light on what you can expect to see when taking this game-changing weight loss drug
Habitual Team
min read
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Quick summary

Mounjaro, the brand name for the drug tirzepatide, is becoming an increasingly popular choice for people looking to lose weight. Having launched in the UK in February 2024, it may be even more effective than other weight loss drugs like Wegovy and Ozempic.

That said, taking Mounjaro isn’t an instant win, not a short-term solution. Weight loss, whether you are using medication or not, is a longer journey. It can take weeks, even months, to see the real benefits and impacts of weight loss on your general health. 

So what can you expect to see as you start taking Mounjaro? Here we share a rough weekly guide for your first eight weeks and beyond, the benefits you’ll start to see, and how you can use this time to establish good habits. 

Mounjaro weeks 1 & 2

You’re at the start of your journey, with a long road ahead of you—but you should feel positive about making a proactive decision to address your weight and reach a healthy target weight. 

Weeks 1 and 2 are a chance for you to really get used to taking Mounjaro, and to set out what you want to achieve by taking the medication. In terms of weight loss, patients in one large trial saw just less than 1% body weight loss per week in the first four weeks, which translates to about 1kg per week in the group studied.[3]

On a physical level, your body needs these first few weeks to get used to taking the medication. You are starting off on a dosage of 2.5mg, the entry level titration for Mounjaro. Everyone experiences the medication differently, and some people won't experience side effects at all, but you may start experiencing common side effects at this time, to varying degrees of intensity. Nausea, vomiting, and diarrhoea, while unpleasant, are not unexpected. There are many things you can do to help combat these side effects—including keeping a close eye on the types of food you are eating and, in some cases, taking an antiemetic medication for cases of more severe nausea. You should consult a healthcare professional before taking any medications at the same time as Mounjaro.

On the plus side, you’ll likely start to notice the primary benefit of Mounjaro—the enduring feeling of fullness that will stop you from overeating. Now, this benefit will be most noticeable in the days immediately following your injection, but at may start to wear off 4 or 5 days after. This is because levels of tirzepatide will be spiking when you inject and then falling over the subsequent days, rather than remaining at a steady state.

The first few weeks are also important for establishing the habit and routine around which you take your medication. At the start, choose an injection day, ideally a time when you know that you’ll be at home and when it fits around your existing routine. If you’re the forgetful type, set a reminder on your phone or put up a post-it note somewhere that’ll remind you. 

Weeks 3 & 4

You’ve got the first two weeks under your belt, and you’re still taking a 2.5mg dosage. Weight loss at this stage is likely to be minimal, but it will already start to take its effect. After 4 weeks, the average weight loss seen in trials is just under 4% of starting body weight.[3] You may start feeling different, but bear in mind that this may be too small to really notice any physical differences in your body. 

At this stage, however, the tirzepatide in your body is starting to reach a steady state. That means that, rather than spiking and falling, levels remain consistent—meaning that the feeling of fullness should endure throughout the week. 

Now that your weight loss journey is well underway, you can take time in these weeks to look further and really set out what you want to achieve by taking Mounjaro. You can set goals and expectations—such as the target weight that you are looking to achieve. Beyond just a weight goal, you might also want to think about other aspects of your general health you want to improve. This might be your sleep hygiene, your mental health, your fitness, or playing sports that you used to play. These things can act as a great motivation to keep going when weight loss might start to lag.

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Weeks 5 & 6

Having completed your first month on Mounjaro, you may be ready to increase your dosage up to 5.0 mg, providing that you are coping well on the lower dosage and not experiencing severe adverse side effects. 

Of course, increasing your dosage may start to bring back some of these side effects as your body gets used to the increase. That said, this is also the stage when weight loss can start to really take effect. 

Physically, you may notice that parts of your body are looking more notably slimmer, with muscles becoming more defined. At week 6, the weight loss seen in the research is about 5-6% of starting weight. You also may experience secondary benefits of being at a healthier weight, such as better sleep hygiene, mental health, and all round fitness. This is hopefully a great reminder of the journey you are on and the rewards to be gained from persistence. 

Weeks 7 & 8

For weeks 7 and 8, you should continue at a 5mg dosage, providing that you are coping fine at this higher titration. 

You’ll really start to see the effects of weight loss here—after 8 weeks, average weight loss is around 6-7% of starting weight.[3] At the same time, new healthy habits that might have felt forced or challenging may start to feel like the norm. The 21/90 rule dictates that it takes 21 days to form a habit, and 90 days to make it a permanent lifestyle change. So your new found love for vegetables, or your 30 minute jog to work—these are hopefully your new normal. 

Weeks 9 & beyond

After your first 8 weeks, you may wish to increase again to 7.5mg. This titration happens at 2.5mg increments over a four week period—up to 7.5mg, then 10mg, and so on up to 15mg as the maximum dosage.[2] This increase should only happen at the recommendation of a medical professional, in collaboration with you based on the side effects you are experiencing. 

It’s important to remind yourself here of how far you have come—not just in terms of total weight lost (on average 6% of your body weight after 2 months [3]) but also in terms of healthy new habits. 

If you continue titrating up your dosage, you will likely see around 11% body weight loss at four months, and getting closer to 20% weight loss at eight months.

But you still have some way to go. You need to take Mounjaro for up to a year in order to see its full effects—an average of 21% body weight loss. Along the way, there may be hiccups, whether that’s lapsing back into old ways, or even hitting the so-called weight loss plateau (when your body stops losing weight and may even start putting it back on). But with well-established goals in mind, your healthy future is in sight. 


[1] Frias, J., Davies, M., Rosenstock, J., et al (2021). Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes, N Engl J Med 2021; 385:503-515. Accessible here

[2] How to use Mounjaro,, retrieved February 23rd 2024. Accessible here

[3] Jastreboff, A., Aronne, L., Ahmad, N., et al (2022). Tirzepatide Once Weekly for the Treatment of Obesity, N Engl J Med 2022; 387:205-216. Accessible here

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