Why Am I Not Losing Weight On Mounjaro?

The most common reasons for not losing weight on Mounjaro (tirzepatide) include;  

• being on too low a dose  

• consuming more calories than you are burning 

• hitting a weight loss plateau 

• taking other medications that promote weight gain 

• underlying medical conditions (hypothyroidism or PCOS/PMOS affecting your response) 

Most people who experience slow progress can resolve it by reviewing their dose, diet, or both. We cover each cause with specific, actionable steps.  

If you have been on a stable dose for 8 or more weeks without meaningful weight loss, speak to your prescriber at The Family Chemist to reassess your treatment plan. 

How Much Weight Should I Be Losing on Mounjaro?

 Expected weight loss on Mounjaro injections varies by dose, diet, and individual metabolism. The SURMOUNT-1 trial found that average body weight reduction was between15 to 22.5% over 72 weeks of doses. 

 Expected Mounjaro weight loss by phase: 

Reasons you’re not losing weight on Mounjaro

1. You are still eating above your calorie needs

Mounjaro suppresses appetite but does not eliminate hunger entirely. If your calorie intake remains above maintenance level, weight loss will stall regardless of the medication.  

This is the most common reason for slow progress, especially in the first 4–8 weeks. 

What to do: Track intake for 1–2 weeks; aim for a 500–750 kcal daily deficit. Focus on protein-rich, high-fibre foods that work with Mounjaro’s satiety effect. We have a calorie deficit calculator that can help you with this.  

2. Low physical activity

As you lose weight your basal metabolic rate decreases, physical activity such as resistance training is important for burning calories and maintaining muscle mass. 

A lack of physical activity can slow your metabolism, making it harder to lose weight. 

What to do: add exercise in your weekly routine, ideally aim for 150 minutes of moderate-intensity activity per week including at least two resistance training sessions. 

3. Missed or delayed doses

Mounjaro’s appetite-suppressing effect depends on stable blood levels of tirzepatide. Even one missed dose per month can reduce its effects. 

Pick a day and time for your injection that you can easily stick to, this ensures a consistent routine.  

If you miss a dose by more than 4 days, do not double up, instead inject on your next scheduled day. 

4. An underlying medical condition

Hypothyroidism, PCOS and Cushing’s syndrome can independently affect weight loss. If you have not lost weight after 8 weeks on a stable dose, ask your GP for thyroid function testing and a hormonal review. 

What to do: Managing these conditions often significantly improves the response to GLP-1 medications. The Family Chemist clinicians can flag this and refer you appropriately. 

5. You have hit a weight loss plateau

A plateau of 3+ weeks despite no change in diet or physical activity is normal because your body adapts to weight loss by reducing energy expenditure. Check your calorie intake has not crept up, this is the most common hidden cause. 

What to do: If intake is controlled and plateau persists beyond 4 weeks, speak to your prescriber about a dose adjustment. 

6. Your dose is too low

Mounjaro starts at 2.5 mg, some patients, particularly those with higher starting body weight or insulin resistance, may require a higher dose such as 7.5 mg or above before experiencing significant appetite suppression. 

If you have been on the same dose for 4+ weeks with settled side effects and stalled weight loss, your dose being too low is a likely cause. 

What to do: Speak to your prescriber at The Family Chemist about moving to the next dose level. 

Medications that promote weight gain

There are several commonly prescribed medications that can promote weight gain or insulin resistance which counteract the effects of Mounjaro. If you are taking any of the following alongside your Mounjaro prescription, this may be why your weight loss is slower than expected. 

• Corticosteroids (prednisolone, dexamethasone) – cause fluid retention and increased appetite
• Antidepressants (particularly mirtazapine, amitriptyline, some SSRIs) – associated with weight gain in a significant proportion of patients 
• Antipsychotics (olanzapine, quetiapine, clozapine) – among the highest weight-gain risk medications
• Insulin and some other diabetes medications (sulphonylureassuch asgliclazide) 
• Beta-blockers (propranolol, atenolol) – reduce metabolic rate and can cause fatigue
• Some hormonal contraceptives – particularly injectable contraception (Depo-Provera)

What to do: Do not stop any prescribed medication without medical advice.  

Speak to your GP or prescriber at The Family Chemist about whether alternatives exist or whether your Mounjaro dose should be adjusted.  

Our clinicians can review your full medication list for interactions and weight-related effects. 

Poor Sleep and High Stress 

Chronic sleep deprivation and psychological stress both raise cortisol levels which can directly counteract Mounjaro’s appetite-suppressing mechanism. 

Sleep

When you sleep fewer than 6–7 hours per night, your body increases production of ghrelin (the hunger hormone) and reduces leptin (the satiety hormone). This makes you feel hungrier even while using Mounjaro and therefore lead to an increased calorie intake. 

Stress

High cortisol promotes fat storage particularly around the abdomen and increases cravings for high-calorie, high-sugar foods.  

For patients experiencing significant life stressors, this cortisol-driven eating can fully offset the appetite suppression from the medication. 

What to do: Aim for 7–9 hours of sleep per night. If stress is a significant factor, speak to your GP or a counsellor.  

Our nutritional coaching service at The Family Chemist includes lifestyle support alongside your prescription. 

What to eat on Mounjaro to maximise weight loss 

Mounjaro suppresses appetite, but what you eat during the smaller windows of hunger you do experience matters. Working with the medication’s effects rather than against them can meaningfully accelerate your results.

Foods to eat more of

Foods to limit or avoid 

Practical eating tips on Mounjaro: 

• Eat protein first at every meal -it supports satiety and reduces total calories eaten.
• Stop eating as soon as you feel full – Mounjaro makes it easier to recognise this signal and use it.
• Avoid large meals late at night – Mounjaro slows gastric emptying and large late meals can worsen nausea.
• Stay well hydrated and have fibre in your diet – constipation is a common side effect and hydration and fibre intake significantly reduce it. 
• If nausea is an issue, eat smaller, more frequent meals and avoid fatty or spicy food on injection day.