Mounjaro Week by Week: What to Expect

Starting Mounjaro? You may be wondering when you’ll start to notice changes. Everyone responds differently, but this week-by-week guide explains what you could expect as your treatment begins, including weight loss, appetite changes and side effects.

Article summary:

• Everyone’s body responds differently to Mounjaro. Weight loss may be slower at the start of your treatment while your body adjusts.
• Progress might not be as visible at the beginning, which is why it’s better to track weight loss over a longer period of time.
• You may experience side effects when you first start taking Mounjaro. They often ease as your body gets used to the medicine, but may return when you increase your dose.

Mounjaro (tirzepatide) is a medicine that was first used to help people with type 2 diabetes. In November 2023, it was also approved in the UK to treat obesity, with specific eligibility criteria. [1]

What to Expect from Mounjaro Results: Week by Week

Everyone’s weight loss journey with Mounjaro is unique. For example, you may notice changes to your appetite before you see changes on the scales.

The starting dose of Mounjaro is 2.5 mg once a week for the first 4 weeks. After this, you can request to increase your dose, providing you’re tolerating the side effects well. However, you don’t need to automatically increase your dose every 4 weeks. You should always balance treatment effectiveness with your ability to manage your side effects, and in some cases, this means staying on a lower dose for longer before moving up. [1]

Week 1

Expected Weight Loss

You’ll start on the 2.5mg dose, which is designed to introduce your body to Mounjaro. It’s not intended to give you significant weight loss results to begin with, although some people do see some scale movement.

As much as you’d like to track your progress, try your best not to focus on day-to-day fluctuations. Instead, take a broader look at your journey over the coming weeks and pay attention to how your body responds to your treatment.

Guidance states that if you use an oral contraceptive pill while on Mounjaro, you should also use a barrier method, such as condoms, for 4 weeks after starting medication, and for 4 weeks after every dose increase. [6]

Appetite Changes

You may notice that you feel fuller for longer or have a slightly reduced appetite in the first week, but equally, these changes might not be major. You could find that smaller plates are more satisfying or you don’t think about food and eating as often.

Side Effects

Some people experience side effects soon after their first dose, which are usually mild and temporary. These may include:

• Nausea
• Vomiting
• Diarrhoea
• Slight headache
• More tired than usual

Side effects are often most noticeable when starting treatment and may improve as your body adjusts. [2]

Week 2

Expected Weight Loss

It’s difficult to attach a set amount of weight loss to any week, and by the end of week 2, any changes you may notice are likely to still be quite subtle.

Mounjaro is a treatment that requires you to make lifestyle changes to support your goals. This medicine works best when it’s paired with regular exercise and a reduced calorie-diet.

Appetite Changes

Appetite suppression may increase, and smaller portions could be more satisfying. You may go longer between meals without feeling hungry or feel less interested in food. However, it’s still early days and you may not find that your appetite has changed that much yet.

Side Effects

You may still experience some of the same side effects from week 1 like nausea, diarrhoea, mild constipation or softer stools. These effects can vary from person to person. [2]

Eating smaller portions, cutting down on foods which could upset your stomach and staying hydrated with plenty of water may be helpful.

Contact your GP or call 111 if:

• You have been vomiting for more than a couple of days
• You have signs of dehydration, such as dark urine or urinating less than usual

Weeks 3 and 4

Expected Weight Loss

After almost a month of taking Mounjaro, you may find that your weight loss is starting to become more noticeable. Whether it first appears in your face or areas on the body, your overall body composition may have started to change.

Appetite Changes

Along with introducing smaller, more balanced meals into your diet, now’s a great time to build a routine that involves regular exercise. Moving your body and keeping active while taking Mounjaro is a useful way to help you on your journey and support your treatment.

Mounjaro should be accompanied by increased physical activity. Eating enough protein and enjoying a rich, varied diet is important for preserving lean muscle mass. [3] Focus on:

• Leafy greens (kale, spinach, lettuce)
• Whole grains
• Lean proteins (chicken, fish, eggs)
• Colourful vegetables (bell peppers, carrots, broccoli)

Side Effects

If you’ve been experiencing digestive side effects like nausea or tummy pain, you may notice them start to settle as your body gets used to the treatment. There’s a chance that they could return if and when your dose increases.

Our team of healthcare professionals will review your 4-week progress when you order your next dose, to ensure that if you decide to increase your dose, it’s safe and appropriate for you to do so. [4]

Weeks 5-8

Expected Weight Loss

Around this point in some people’s journey, there may be clearer weight loss especially if you’ve been moved up to the next dose. Of course, progress around weeks 5-8 could look different for everyone. You may have increased your dose to 5mg by the end of week 8. By week 8, the data suggests patients will have lost around 6% of their body weight at a steady rate. [5]

Mounjaro is a longer-term treatment and it can take weeks, or even months to see results. In a 72-week clinical trial, participants who took tirzepatide alongside making lifestyle changes achieved average weight reductions of 15.0%, 19.5% and 20.9% at the highest doses studied. [5]

It’s understandable to want to see results sooner rather than later, but this study offers a gentle and reassuring reminder that things take time. Try not to focus on day-to-day changes, especially in the early weeks, which may be harder to spot and make you feel like you’re not making progress. Instead, be patient and do your best to trust the process. [5]

Appetite Changes

You may crave fewer snacks or sweet treats. This is because you could feel fuller for longer as Mounjaro (tirzepatide) helps slow down stomach emptying by mimicking the digestive hormones. [4]

Side Effects

Side effects may often become less noticeable over time, but they can reappear after a dose increase. [3]

Drink plenty of fluids, especially if you’re vomiting or experiencing diarrhoea, to help reduce the chance of dehydration. Seek urgent medical advice for severe, persistent stomach or back pain, as this may be a sign of pancreatitis, which is a rare but serious side effect. [6]

Weeks 9-12

Expected Weight Loss

For some people, the signs of weight loss may be much clearer now, but this isn’t necessarily the same experience for everyone taking Mounjaro. Try not to attach a goal weight on the scale to your week-by-week progress.

Again, you may have increased your dose several more times by the end of week 12, but it’s okay if you haven’t. You don’t have to increase every 4 weeks if your current dose is working well and you’re tolerating your side effects.

Appetite Changes

As you continue to prioritise balanced meals, increased water intake and high-protein foods, you should notice that you have fewer cravings.

Side Effects

Side effects around this point are likely quite mild or moderate, but could make a reappearance if you move up a dose. [5]

Long Term Results & Expectations

Expected Weight Loss

Everyone loses weight at different rates, so it’s important to give Mounjaro time to work.

Some people lose weight quickly at first. Others might slow down or stop losing weight for a while (called a weight loss plateau). Some people don’t see results until later, especially if side effects make it harder to exercise regularly or eat a healthy, balanced diet in the beginning.

We’ll check your progress every time you re-order. If you haven’t lost at least 5% of your starting weight by 6 months of treatment, we may suggest stopping Mounjaro and looking at other options that could work better for you.

Appetite Changes

Mounjaro may continue to reduce hunger and cravings and help you feel fuller for longer. That’s why it’s important to do your best to maintain balanced meals, regular exercise and sustainable habits which can support your journey.

Side Effects

Although you’ll probably be well used to side effects by now, you may still be having to manage them. Remember you can speak to your prescriber, or read our blog, to see if there are any medications or methods that could make your Mounjaro side effects easier to tolerate. [5]

Mounjaro Success Stories and Challenges

Even though weight loss medications like Mounjaro have been proven to work in studies, it can be really helpful to hear from real people who have used it. Their stories, challenges and feedback can give you a better idea of what to expect.

Rosie, lost 25kg (56lbs) in 6 months on Mounjaro

“I had gained over five stone since having my three children and had tried every diet under the sun. I finally plucked up the courage to try Mounjaro and it has changed my life. I’ve not only lost four stone but I am happier, more confident, full of energy and able to run around after my children for longer.

Mounjaro has drastically improved my physical, emotional and mental health. Medexpress have been so supportive in my journey and have always been available if I have had any questions.”

 Roisin lost 19.5kg (43lbs) in 3 months on Mounjaro

“Carrying 20 stone at 5ft '5 is a lot of weight for anybody and I was just in pain. I didn't want to get dressed. I didn't want to go out. I wouldn't look in the mirror. I had to do something to change mentally. Otherwise, I was just going to stay in that consistent loop.

I was surprised with how much weight Mounjaro has helped me lose in such a short amount of time. I've changed my eating dramatically. The snacking has seemed to have disappeared because I want to lose weight more than I want the chocolate bar. I never thought I'd lose the amount of weight that I have – if I lose a pound a week, that's great. The pain in my knee seems to have decreased a lot since losing the weight. I don't get any more back pain.

I think it's made me a lot more confident within myself. I actually want to go out and do things. I want to go clothes shopping. I don't want to be at home, I want to be out doing something with my kids. It's been the greatest thing I've ever done for myself, 100%!”

Magdalena lost 22kg (48.5lbs) in 4 months on Mounjaro

“The primary reason [for wanting to lose weight] was being healthy for my kids. There’s a lot of things that I will not be able to do at the weight that I was… I was restricted. I would like to be able to do these things with them to have fun with them; be healthy for them and for myself… to be happy and healthy.

I did try the Cambridge diet, I tried the Keto diet and fasting, but it was just a temporary solution. It had a rebound effect where I lost some [weight] and after that I just regained it back because I wasn't managing it very well. The food noise was still there.

Before, I was struggling to find clothes that fit me because everything was too small. Whereas now I struggle to find clothes that fit me because everything is becoming too loose.”

Mounjaro Results FAQs

Why am I not losing weight on Mounjaro?

Try not to worry. Results can take time, especially while you’re on the starting dose. Weight loss may also vary from person to person for a number of reasons including dose, diet, activity levels, health and how your body responds.

Some people respond more slowly than others. And for some people, Mounjaro simply isn’t the right treatment for them. That’s why if you haven’t lost 5% of your body weight in 6 months, we will talk to you about alternative treatments.

What factors influence Mounjaro's efficacy?

Not everyone will lose weight in the same way or at the same speed when using Mounjaro. This is because many things can affect your results, including your starting weight, pre-existing health conditions, side effects, how active you are and your diet.

How much weight can I lose on Mounjaro in a month?

There’s no guaranteed monthly amount. Weight loss is often gradual, and early changes may be small while your dose is being increased.

How fast can you lose weight on Mounjaro?

Some people notice appetite changes within the first few weeks, while significant weight loss usually develops over a longer period. Your weight may also fluctuate or plateau along the way, which is completely normal.

How long does Mounjaro take to work?

Mounjaro begins working after your first dose, but it may take a few weeks to notice a clear change in appetite or weight. The starting dose is designed to help your body adjust, and your prescriber may gradually increase it if appropriate.

If you are thinking about weight loss medication and want to know what options might be right for you, you can complete a short online consultation on our website. A clinician will review your information and let you know if treatment is appropriate.

At MedExpress, we offer online consultations with regular clinical check-ins, and a range of weight loss treatments including Mounjaro, Wegovy Pen, Wegovy Pill and Foundayo and our team can help you find the right treatment for you.

References

1. Package leaflet: Information for the patient Mounjaro ® 2.5 mg KwikPen ® solution for injection in pre-filled pen Mounjaro ® 5 mg KwikPen ® solution for injection in pre-filled pen Mounjaro ® 7.5 mg KwikPen ® solution for injection in pre-filled pen Mounjaro ® 10 mg KwikPen ® solution for injection in pre-filled pen Mounjaro ® 12.5 mg KwikPen ® solution for injection in pre-filled pen Mounjaro ® 15 mg KwikPen ® solution for injection in pre [Internet]. [cited 2026 Oct 1]. Available from: https://www.medicines.org.uk/emc/files/pil.15481.pdf
2. NHS website. Tirzepatide [Internet]. nhs.uk. 2026 [cited 2026 Oct 1]. Available from: https://www.nhs.uk/medicines/tirzepatide/
3. Farhana A, Rehman A. Metabolic Consequences of Weight Reduction [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2026 Oct 9]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK572145/
4. Your obesity treatment: tirzepatide (Mounjaro®) [Internet]. Cambridge University Hospitals. 2026 [cited 2026 Oct 7]. Available from: https://www.cuh.nhs.uk/patient-information/your-obesity-treatment-tirzepatide-mounjaro/
5. Jastreboff AM, Aronne LJ, Ahmad NN, Wharton S, Connery L, Alves B, et al. Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine [Internet]. 2022 June 4 [cited 2026 Oct 1];387(3):205–16. Available from: https://www.nejm.org/doi/full/10.1056/NEJMoa2206038
6. Mounjaro KwikPen 2.5mg solution for injection in pre-filled pen - Summary of Product Characteristics (SmPC) - (emc) [Internet]. www.medicines.org.uk. [cited 2026 Oct 9]. Available from: https://www.medicines.org.uk/emc/product/15481/smpc