Why Am I Not Losing Weight on Mounjaro or Wegovy? 7 Possible Reasons

Why am I not losing weight on Mounjaro or Wegovy?

Mounjaro (tirzepatide) and Wegovy (semaglutide) are highly effective prescription medicines for weight management, but they do not cause the same amount of weight loss in everyone.

If you have started treatment and the number on the scales is barely changing, or your weight loss has stopped after several months, it does not necessarily mean that the medicine is not working.

There are several possible explanations, including being on an early dose, inconsistent dosing, changes in appetite or calorie intake, reduced physical activity, fluid fluctuations, underlying health factors and individual differences in response.

NICE recommends that weight management medicines are used alongside a reduced-calorie diet and increased physical activity. For tirzepatide and semaglutide, NICE also provides guidance on reviewing treatment when weight loss is less than 5% of starting body weight after six months on the highest tolerated dose.

So, if Mounjaro or Wegovy does not appear to be working, the first step is not necessarily to abandon treatment. It is to understand why your weight loss may have slowed or been limited.

Here are seven possible reasons.

1. You are still on a lower dose

One of the most common reasons people think Mounjaro or Wegovy is not working is simply that they are still early in the dose-escalation process.

These medicines are generally started at a lower dose and increased gradually. This is designed to improve tolerability, particularly by reducing the likelihood or severity of gastrointestinal side effects.

For example, injectable Wegovy is normally increased gradually from 0.25 mg through several dose levels before reaching the usual 2.4 mg maintenance dose. The current UK product information also allows an increase to 7.2 mg once weekly in certain adults with obesity who need additional weight-management treatment.

Tirzepatide is also increased gradually, with maintenance doses of 5 mg, 10 mg or 15 mg once weekly.

This means you should not necessarily expect the same degree of appetite suppression or weight loss at the beginning of treatment as you might at a maintenance dose.

Do not increase your dose faster than prescribed. Dose escalation should be determined by your prescriber based on your response, tolerability and medical circumstances.

If you have only recently started Mounjaro or Wegovy, it may simply be too early to judge the full effect.

2. Your weight loss has reached a plateau

Weight loss is rarely completely linear.

You might lose several kilograms during the first few months, then notice that your weight stays around the same level for several weeks.

This is known as a weight-loss plateau.

A plateau does not automatically mean that Mounjaro or Wegovy has stopped working.

As your body weight decreases, your energy requirements can also change. Your appetite, activity levels, food intake and other physiological factors can change over time. The result can be a period where your weight remains relatively stable despite continuing treatment.

It is therefore important to look at the overall trend, rather than judging treatment based on one or two weeks.

For example, a person might weigh:

• 100 kg when starting treatment
• 96 kg after two months
• 93 kg after four months
• 93 kg after five months

The fact that their weight has remained around 93 kg for a month does not erase the 7 kg they have already lost.

A plateau can sometimes be addressed by reviewing nutrition, physical activity, adherence, sleep, medication and the current treatment plan with a clinician.

3. You may be eating more calories than you realise

Mounjaro and Wegovy can reduce appetite and help people feel fuller, but they do not make calories irrelevant.

Both medicines are intended to be used alongside dietary and lifestyle measures. NICE specifically recommends combining weight-management medicines with a reduced-calorie diet and increased physical activity.

One reason weight loss can slow is that calorie intake gradually increases without the person necessarily noticing.

This can happen when:

• portion sizes increase
• snacks become more frequent
• calorie-dense foods are eaten regularly
• liquid calories are overlooked
• alcohol intake increases
• weekend eating differs substantially from weekday eating
• appetite suppression becomes less noticeable over time

You do not necessarily need to count every calorie forever.

However, if your weight loss has stalled, reviewing your food intake for a short period can sometimes reveal patterns that are easy to miss.

The goal should not be extreme restriction. An overly restrictive diet can make it harder to obtain adequate protein, fibre, vitamins and minerals and may be difficult to maintain.

4. You are not taking the medicine consistently

Consistency matters with prescription weight-management treatment.

If doses are regularly missed, delayed or taken incorrectly, exposure to the medicine may not be as intended.

This can potentially affect appetite control and your overall treatment response.

If you have missed doses, experienced problems with your prescription, struggled with your injection technique or are unsure whether you are administering the medicine correctly, speak with your prescriber or pharmacy team rather than attempting to compensate by taking extra medicine.

It is also important to follow the specific instructions for your prescribed product because missed-dose recommendations can vary.

If you are using an injectable treatment, make sure you understand:

• when to administer your dose
• how to store your medicine
• how to use the injection device
• what to do after a missed dose
• when you should contact your healthcare professional

If you are unsure whether you are using your treatment correctly, a clinical review can help.

5. Your physical activity has changed

You do not need to become an elite athlete for Mounjaro or Wegovy to work.

However, physical activity remains an important part of weight management.

NICE recommends increased physical activity alongside weight-management medicines.

Some people become less active without realising it when they eat less.

For example, you might:

• walk fewer steps
• spend more time sitting
• stop exercising because of fatigue or nausea
• reduce resistance training
• become less active during periods of stress or illness

This can influence your overall energy expenditure.

Resistance training is particularly useful during weight loss because it can help support muscle mass and strength.

A balanced approach may include walking or other aerobic activity alongside resistance exercises, adjusted to your fitness level and medical circumstances.

You do not have to exercise excessively to lose weight, but maintaining regular movement can support the overall treatment strategy.

6. Other factors may be affecting your weight

Weight is influenced by much more than food and exercise.

If your weight loss is unexpectedly limited, a clinician may need to consider other factors that could be contributing.

These can include:

Sleep

Poor or insufficient sleep can affect appetite, energy levels and eating behaviour.

Stress

Long-term stress can influence eating patterns, sleep and physical activity.

Other medicines

Some medicines can affect body weight or appetite. If you take several prescription medicines, your clinician can review whether any could be contributing.

Medical conditions

Certain medical conditions can influence weight or make weight management more difficult.

Examples may include some endocrine disorders and metabolic conditions.

This does not mean that every person who struggles to lose weight has an underlying medical problem. However, persistent or unexplained difficulty losing weight may justify a broader clinical assessment.

Type 2 diabetes

People living with type 2 diabetes may lose weight at a different rate from people without diabetes. NICE specifically advises clinicians to be aware that people with type 2 diabetes may take longer to lose weight with tirzepatide.

This is one reason treatment response should be assessed individually rather than compared directly with another person's results.

7. You may be a lower responder to the medicine

Perhaps the most frustrating possibility is that you simply do not respond as strongly as another person.

Clinical trials report average weight loss across groups of participants. They do not mean that every individual will lose the same percentage of their body weight.

Some people experience substantial weight loss. Others experience a more modest response.

Your starting weight, genetics, metabolic health, diabetes status, lifestyle, adherence, dose, treatment duration and other individual factors can all contribute to the outcome.

This is why comparing your weight loss with someone else's results on social media can be misleading.

Someone might report losing 20 kg on Mounjaro, while another person loses considerably less. Neither result necessarily tells you whether the treatment is appropriate for you.

The more important question is:

Am I achieving enough benefit from treatment to justify continuing it?

That is something your prescriber can assess based on your starting weight, percentage weight loss, dose, duration of treatment, side effects, health improvements and overall goals.

How long does Mounjaro or Wegovy take to work?

There is no single timeline that applies to everyone.

Some people notice reduced appetite relatively early, while measurable weight loss may take longer. Others may experience gradual changes over several months.

It is important to remember that the initial doses are primarily part of the dose-escalation process, rather than necessarily representing the final maintenance dose.

For injectable Wegovy, the current UK product information describes a gradual 16-week escalation to 2.4 mg, with the option of 7.2 mg in certain adults with obesity when additional treatment is appropriate.

Tirzepatide is similarly titrated gradually, with the dose increased by 2.5 mg every four weeks when appropriate and tolerated.

This is why judging the success of treatment after only a few weeks can be premature.

When should you speak to your prescriber?

You should discuss your progress with your prescriber if:

• you have seen little or no weight change despite taking your medicine consistently
• your weight loss has plateaued for a prolonged period
• your appetite suppression has significantly changed
• you are struggling with side effects
• you are unable to reach or tolerate the intended dose
• you have repeatedly missed doses
• you are unsure how to use your injection
• you have concerns about other medicines or health conditions
• you are considering increasing your dose yourself

NICE guidance recommends reviewing response to tirzepatide after six months on the highest tolerated dose. If less than 5% of initial body weight has been lost, the clinician should discuss why the response may have been limited and consider whether continuing treatment is appropriate.

Similar guidance applies to semaglutide, where NICE recommends considering stopping treatment if less than 5% of initial body weight has been lost after six months.

This does not mean that everyone who loses less than 5% must automatically stop treatment. Clinical decisions should consider the individual's circumstances, benefits, risks and treatment response.

Should I switch from Mounjaro to Wegovy if I am not losing weight?

Not necessarily.

Mounjaro contains tirzepatide, while Wegovy contains semaglutide. They work through different mechanisms, although both influence pathways involved in appetite and weight regulation.

If you are not losing weight, switching medication may sometimes be considered, but it should not be the first assumption.

Before changing treatment, your clinician may want to review:

• your current dose
• how long you have been taking it
• your dosing consistency
• your dietary intake
• physical activity
• side effects
• other medicines
• medical conditions
• your actual percentage weight loss
• whether you have reached a genuine treatment plateau

NICE specifically notes that people with a lack of response or inability to tolerate tirzepatide may be considered for specialist weight-management services or alternative pharmacological management.

If you are currently using a weight-loss injection, you can also read our guide to weight loss injections and what you need to know.

Does Mounjaro stop working?

Mounjaro does not necessarily "stop working" simply because weight loss slows.

A reduction in the rate of weight loss can be a normal part of longer-term weight management.

However, if appetite has returned significantly or your weight has remained unchanged for an extended period, it is worth discussing your treatment with your prescriber.

Do not increase your Mounjaro dose yourself.

The appropriate dose depends on your individual response and tolerability.

Does Wegovy stop working?

The same principle applies to Wegovy.

Weight loss can slow or plateau over time, even when treatment continues.

A plateau should be assessed in the context of your overall weight trajectory rather than based on a short period of stable weight.

If you are concerned that Wegovy is no longer controlling your appetite or your weight has stopped changing, speak with your clinician before making any changes to your treatment.

You can also read our guide to Wegovy and its role in weight management.

What should I do if Mounjaro or Wegovy is not working?

If you are concerned that your weight-loss treatment is not working, avoid making sudden changes to your dose or stopping treatment without medical advice.

Instead, arrange a clinical review.

A clinician can assess your treatment response and look at the bigger picture, including your percentage weight loss, current dose, treatment duration, side effects, eating pattern, activity levels and other relevant health factors.

If appropriate, your treatment plan may be continued, adjusted or reconsidered.

For more information, see our guide to weight loss injection side effects.

Frequently Asked Questions

Why am I not losing weight on Mounjaro?

Possible reasons include being on an early dose, inconsistent dosing, a weight-loss plateau, increased calorie intake, reduced physical activity, other medicines or health conditions, and individual differences in response.

Why am I not losing weight on Wegovy?

You may be early in treatment, still progressing through dose escalation, experiencing a temporary plateau or receiving a smaller-than-average response. Your diet, activity levels, adherence and other health factors can also influence your results.

How long does Mounjaro take to work for weight loss?

There is no universal timeline. Some people notice appetite changes early, while measurable weight loss develops progressively. Treatment is gradually titrated, so the early doses should not necessarily be compared with the full maintenance dose.

How long does Wegovy take to work?

Wegovy is gradually increased over several weeks to reduce the likelihood of gastrointestinal side effects. Weight loss can develop progressively rather than immediately, so it may be too early to judge the treatment during the initial stages.

What is a normal weight-loss plateau on Mounjaro?

There is no specific number of weeks that defines a normal plateau. Weight can remain stable temporarily during long-term weight loss. A prolonged plateau should be reviewed alongside your dose, treatment duration, diet, activity and overall response.

Should I increase my Mounjaro dose if I am not losing weight?

No. Do not increase your dose without advice from your prescriber. Tirzepatide is designed to be increased gradually according to the prescribed schedule and individual tolerability.

Should I stop Wegovy if I am not losing weight?

Not necessarily. Your clinician should assess your overall response before deciding whether treatment should continue. NICE recommends considering treatment response after six months and assessing whether at least 5% of starting body weight has been lost.

Can you still lose weight after a plateau?

Yes. A period of stable weight does not necessarily mean that further weight loss is impossible. Reviewing your treatment, nutrition, activity and other factors may help determine why progress has slowed.

Is Mounjaro better than Wegovy if I am not losing weight?

Not automatically. Different people respond differently to each medicine. If your response is inadequate, your clinician can assess whether continuing, adjusting or considering an alternative treatment is appropriate.

The bottom line

If you are not losing weight on Mounjaro or Wegovy, do not immediately assume that the medicine has failed.

The most common explanations can include being early in treatment, still increasing the dose, experiencing a normal weight-loss plateau, changes in food intake or physical activity, inconsistent dosing, other health factors or simply having a lower individual response.

The most useful way to assess treatment is not by comparing yourself with someone else's results. It is by looking at your own weight trajectory, treatment duration, dose, adherence, health goals and overall response.

If you have been taking your treatment consistently and have seen little or no meaningful weight loss, it is worth having a clinical review. NICE specifically recommends assessing treatment response after six months at the highest tolerated dose, with less than 5% weight loss prompting a discussion about whether continuing treatment remains appropriate.

For more information about prescription weight-management treatment, explore SynovaMed's weight loss injection service or contact our clinical team to discuss your options.