The second week is often when the excitement of starting treatment turns into questions. Is Mounjaro supposed to be working by now? Why has the number on the scales barely changed? Should side effects be better or worse than they were last week?
Week 2 is still very early in your treatment. This guide explains what you may notice during your second week, what is considered expected, and when it is worth speaking to your prescriber.
Key things to know
- In your second week, you take your second injection at the same starting strength. Your dose does not normally change yet.
- The licensed starting dose is 2.5mg once weekly. After 4 weeks, the dose can be increased to 5mg if your prescriber considers this appropriate.
- Tirzepatide has a half life of around 5 days. Steady state exposure is reached after around 4 weeks of once weekly treatment.
- Changes in appetite can happen early, but weight loss varies from person to person and usually takes longer to become noticeable.
- Having little or no change in your weight during week 2 does not mean that Mounjaro is not working.
- Never increase your dose, inject earlier than prescribed or take an extra dose to try to speed up weight loss.
Where you actually are in week 2
This is an important detail that many week 2 guides leave out.
The licensed starting dose of Mounjaro is 2.5mg once weekly. After 4 weeks, it is normally increased to 5mg once weekly. If further increases are needed, they are made in 2.5mg steps after at least 4 weeks on the current dose.
This means that your second week is simply your second injection at the same strength as your first. There is no routine dose increase at this point.
It can be reassuring to know this because you are not expected to have reached your final dose or seen your full treatment response after only 2 weeks. Your response can develop over time, and your prescriber will decide whether and when a dose increase is suitable.
| Week | What is happening |
|---|---|
| Week 1 | First injection. Tirzepatide begins to build in your body. |
| Week 2 | Second injection at the same strength. Tirzepatide levels continue to build. |
| Week 3 | Third injection. You may notice changes in appetite or how much food feels comfortable to eat. |
| Week 4 | Fourth injection. Steady state exposure is reached around this point with once weekly dosing. Your prescriber may then review your treatment. |
Why week 2 can feel quiet
Tirzepatide is absorbed gradually after the injection. Maximum blood concentrations are reached between 8 and 72 hours after a dose, while steady state exposure is reached after around 4 weeks of once weekly treatment. Its half life is approximately 5 days, which supports once weekly dosing.
This means that after two injections, the amount of medicine in your body is still building towards its steady state level. However, this does not mean that you will feel no effect during week 2. Some people notice changes in appetite earlier, while others notice little difference at first.
Clinical research has assessed appetite measures at different time points, but there is no reliable rule that says everyone will experience reduced hunger in week 1 or increased fullness in week 3. Your experience can be different from someone else's.
What about day 2?
If you mean the second day after your injection, you may notice some changes around this time because tirzepatide reaches maximum blood concentrations between 8 and 72 hours after a dose. However, there is no specific day when everyone should feel an effect.
You might notice less interest in food, feeling full sooner, nausea or other gastrointestinal symptoms. You might also notice very little. Both can happen, so there is no need to worry if your second day does not feel noticeably different.
What people commonly notice in week 2
Appetite and food noise
A change in appetite is one of the effects you may notice during the early weeks of treatment. Some people also describe less frequent thoughts about food, sometimes called "food noise".
You may find that portions feel more filling or that you are less interested in snacking. However, not everyone experiences these changes at the same time or to the same degree.
Decreased appetite is listed as an adverse reaction to tirzepatide, so a lower appetite can occur during treatment. It is still important to eat enough nutritious food and drink enough fluids.
The scale
Try not to judge your treatment by the scales after only 2 weeks.
Weight can change from day to day because of factors such as fluid levels, food intake and bowel movements. Any early change in weight does not necessarily represent fat loss, and little or no change in the first few weeks does not mean that you will not lose weight later.
The headline SURMOUNT 1 results are useful for showing what happened over a much longer period. In that study, average weight loss after 72 weeks was 16.1kg with 5mg, 22.2kg with 10mg and 23.6kg with 15mg in the relevant treatment groups. These figures should not be treated as a monthly target or divided by 72 to predict your weekly weight loss.
Injection site reactions
Redness, itching or other reactions at the injection site can occur with Mounjaro. In pooled placebo controlled weight management studies, injection site reactions occurred in 8.0 percent of people taking tirzepatide compared with 1.8 percent taking placebo. Most were mild or moderate, and none were serious.
You can rotate your injection site according to the instructions provided with your pen. If you develop a severe or unusual reaction, speak to a healthcare professional.
Energy, sleep and mood
Some people feel tired during treatment. Fatigue is listed as a common adverse reaction to tirzepatide.
If your appetite has dropped significantly, make sure you are still eating regular, balanced meals and drinking enough fluids. Feeling very weak, dizzy or unusually tired should not simply be assumed to be a normal part of starting Mounjaro. Speak to your prescriber if symptoms are severe, persistent or getting worse.
How much weight can you lose on Mounjaro in a month, in kilograms?
This is one of the most common questions about week 2 on Mounjaro. The honest answer is that there is no single amount of weight that everyone should expect to lose during the first month.
Clinical trials such as SURMOUNT 1 measured weight loss over much longer periods rather than setting a specific target for the first 4 weeks. During the first month, treatment begins at the licensed starting dose of 2.5mg once weekly.
For context, participants in SURMOUNT 1 started at an average weight of around 105kg. After 72 weeks, mean weight loss was 16.1kg with 5mg, 22.2kg with 10mg and 23.6kg with 15mg. These are long term trial results and are not a prediction of what you will lose in your first month.
The NHS advises that a steady rate of around 0.5kg to 1kg per week can be a reasonable weight loss target for many people. However, this is general weight management guidance, not a Mounjaro target, and your individual rate can be different.
Faster weight loss is not automatically better. Rapid weight loss can be associated with problems such as gallstones, so it is better to focus on steady progress and adequate nutrition rather than trying to lose as much as possible as quickly as possible.
Mounjaro contains tirzepatide, which acts on both GIP and GLP 1 receptors. It can affect appetite and food intake, while also having effects on blood glucose regulation. The response develops differently from person to person and should be assessed over time rather than judged by a single week.
Mounjaro is licensed for weight management alongside a reduced calorie diet and increased physical activity. Building healthy eating and activity habits alongside treatment can support your overall weight management plan.
In short, week 2 may feel very early, especially if you have seen little change on the scales. Keep taking your treatment as prescribed and give yourself time to see how your body responds.
For further detailed guidance on Mounjaro dosage, weight loss timelines and managing side effects, please refer to our comprehensive Mounjaro injection page and weight loss treatments hub.
Week 2 side effects and how they compare with week 1
Side effects can improve, continue or change during your second week. Knowing which effects are commonly reported can help you understand what you are experiencing.
| Side effect | Frequency in weight management trials |
|---|---|
| Nausea | 24.6 to 29.0 percent on tirzepatide, compared with 8.5 percent on placebo |
| Diarrhoea | 18.7 to 22.5 percent on tirzepatide, compared with 7.8 percent on placebo |
| Constipation | Listed as a very common adverse reaction in the weight management studies |
| Vomiting | Listed as a very common adverse reaction in the weight management studies |
| Fatigue | Listed as common, meaning up to 1 in 10 people |
In the pooled weight management studies, gastrointestinal adverse reactions were mostly mild or moderate. The incidence of nausea, vomiting and diarrhoea was higher during the dose escalation period and decreased over time.
Practical management in week 2
- Smaller meals may be easier to manage if you feel full quickly or have nausea. High fat meals may make gastrointestinal symptoms worse for some people.
- Eat slowly and stop when you feel comfortably full. You do not need to finish a meal simply because there is food left on your plate.
- Drink regularly throughout the day. Vomiting and diarrhoea can lead to dehydration, which can affect kidney function.
- Include nutritious sources of protein as part of your meals to help you maintain a balanced diet.
- If constipation develops, gradually increasing fibre and keeping active may help, provided you can tolerate it.
- If side effects are severe or persistent, speak to your prescriber rather than changing your dose yourself.
Nothing is happening in week 2. Is that normal?
It can be. Week 2 is still very early in treatment, and people respond differently to tirzepatide.
The starting dose is 2.5mg once weekly and is normally used for the first 4 weeks before an increase to 5mg is considered.
You should not assume that Mounjaro has failed simply because your appetite or weight has not changed much during week 2.
The important thing is not to try to make the medicine work faster yourself. Do not increase your dose early, inject more often or take an additional dose. These changes can increase the risk of side effects.
If you are concerned that you are not noticing any effect, discuss it with your prescriber at your next review.
An important week 2 point about contraception
This is particularly important during your first month of treatment.
Tirzepatide delays gastric emptying, and this can affect the absorption of some oral medicines. For women with overweight or obesity who use an oral contraceptive, reduced contraceptive effectiveness cannot be ruled out.
The current UK product information advises using a non oral contraceptive method or adding a barrier method for 4 weeks after starting tirzepatide and for 4 weeks after each dose increase.
Week 2 falls within this first 4 week period. If you use an oral contraceptive and this advice was not discussed when you started treatment, speak to your pharmacist, prescriber or another healthcare professional.
Common week 2 mistakes
- Weighing yourself several times a day and worrying about every small change. Day to day weight changes are normal.
- Eating far too little because your appetite has decreased. You still need enough food and nutrients to support your health.
- Skipping meals completely rather than choosing smaller meals. This can make it harder to maintain a balanced diet.
- Not drinking enough fluids, particularly if you have nausea, vomiting or diarrhoea.
- Comparing your second week with someone else's experience. Mounjaro does not affect everyone in exactly the same way.
- Increasing your dose early because you think the starting dose is not working. Dose increases should only be made according to your prescriber's instructions.
What week 2 is genuinely for
Week 2 is a good time to focus on habits that can support your treatment over the longer term.
- Keep your injection day consistent so that your weekly doses are easy to remember.
- Build meals around nutritious foods, including a source of protein, vegetables, fruit and suitable sources of carbohydrates and healthy fats.
- Make drinking fluids a regular habit, particularly if you have gastrointestinal side effects.
- Start or continue regular physical activity at a level that feels manageable for you.
- Track more than your weight. You could also note your appetite, portion sizes, energy levels and any side effects.
- Keep a note of symptoms or questions to discuss with your prescriber.
- Give your body time to adjust rather than trying to speed up the treatment.
Mounjaro can affect appetite and digestion, but the timing and strength of these effects vary between people. You may notice changes during week 2, or you may notice very little at this stage.
The goal is not to feel the strongest possible effect as quickly as possible. It is to use the medicine safely as prescribed while building healthy habits that you can maintain.
What happens after week 2
Weeks 3 and 4 are still part of the starting phase. You may notice further changes in appetite or gastrointestinal symptoms, but there is no specific week when everyone should suddenly feel a stronger effect.
Around the 4 week mark, your prescriber can review how you are tolerating the 2.5mg starting dose. If appropriate, the dose can be increased to 5mg once weekly. Further increases, if needed, should be made in 2.5mg steps after at least 4 weeks on the current dose. The maximum dose is 15mg once weekly.
Side effects such as nausea, vomiting and diarrhoea can become more noticeable during dose increases and may decrease over time. If you are struggling with side effects, speak to your prescriber before making any changes to your treatment.
For weight management, the UK product information states that if a patient has not lost at least 5 percent of their initial body weight 6 months after titrating to the highest tolerated dose, a decision should be made about whether continuing treatment is appropriate, taking the individual's benefits and risks into account.
Weight loss does not always follow a straight line. Your weight can move up and down because of normal changes in fluid levels, food intake and other factors. If your weight loss slows or you are concerned about your progress, speak to your healthcare professional rather than changing your treatment yourself.
Healthy eating and regular physical activity remain part of the overall treatment plan. Mounjaro is licensed for weight management alongside a reduced calorie diet and increased physical activity.
When to contact your prescriber
| Symptom | Why it matters |
|---|---|
| Severe, persistent abdominal pain, particularly if it spreads to your back | Needs urgent medical assessment because pancreatitis is a possible serious adverse reaction |
| Persistent vomiting or inability to keep fluids down | Can lead to dehydration and may affect kidney function |
| Shakiness, sweating or confusion, especially if you take insulin or a sulphonylurea | May indicate low blood sugar |
| Black or bloody stools | Needs urgent medical assessment |
| Swelling of the face or lips, rash or difficulty breathing | Could indicate a serious allergic reaction and needs immediate medical attention |
| Being unable to eat or drink adequately | May lead to dehydration or inadequate nutrition and should be discussed with a healthcare professional |
Mild nausea or changes in bowel habits can occur during treatment. However, severe, persistent, worsening or worrying symptoms should not simply be ignored or blamed on Mounjaro.
If you develop severe abdominal pain, persistent vomiting, signs of significant dehydration or another serious symptom, seek medical advice promptly. Call 999 in an emergency.
How Mounjaro fits into weight management in the UK
Mounjaro is a prescription only medicine licensed for weight management alongside a reduced calorie diet and increased physical activity. It is also licensed for the treatment of type 2 diabetes. Whether Mounjaro is suitable for you depends on your individual circumstances, and your prescriber will decide whether treatment is appropriate and which dose is suitable.
The diet and activity part of treatment is important. The weight management clinical trials studied tirzepatide alongside reduced calorie intake and increased physical activity, so the results reflect a wider treatment programme rather than the injection alone.
If you are still comparing your options, our weight loss treatments hub sets out the injectable and oral options available in the UK, while the Mounjaro injection page covers the available strengths, storage and what treatment involves.
Week 2 is still an early stage. Try not to judge your entire treatment by the number on the scales or by how you feel on one particular day. Take Mounjaro as prescribed, pay attention to how your body responds and speak to your healthcare professional if you have concerns. Results vary between individuals.