Starting Your Weight Loss Journey - 2.5mg
If you’re reading this, it’s likely your first dose of Mounjaro has just arrived or will be with you soon. This marks the beginning of your treatment, and we’ll guide you through everything you need to know about starting on 2.5mg.
Three key takeaways
- The 2.5mg starter dose is designed to help your body adjust gently while you learn how the pen works.
- Early side effects such as nausea or reflux are common, usually mild, and tend to settle as your body adapts.
- Simple habits around food, movement, and routine can help you get the most from treatment in your first few weeks.
1. Double check your order
When your parcel arrives, open it promptly and confirm:
- the pens feel cold (not frozen or warm)
- the packaging is intact
- the correct strength and quantity have been delivered
If anything looks damaged or warm, refrigerate the pens and contact customer care before using them.
What’s in the box
Your order should include:
- Mounjaro 2.5mg pens
- single-use needles
- alcohol swabs
- instructions for use and storage
If anything is missing, contact customer care. A sharps bin for used needles isn’t included, so make sure you have one ready before your first dose.
Temperature and safety checks
Mounjaro must be kept between 2°C and 8°C. Store it on a middle shelf in the fridge, away from the door where temperatures fluctuate.
If you’d like a full breakdown of fridge storage rules, see our guide to keeping your Wegovy or Mounjaro pen refrigerated.
Read your leaflet before you start
Your patient information leaflet explains:
- how to inject your first dose
- recommended injection sites (you can also read our guide on the best place to inject Mounjaro)
- common early side effects
- how to store, handle, and dispose of the pen
2. Get ready to inject your first dose
Always follow the step-by-step instructions in your leaflet, or use our guide on how to take Mounjaro.
General safety questions
- Bubbles in the pen? Small air bubbles are normal.
- Cloudy or discoloured liquid? Do not use the pen. Contact customer care.
- Pen left out of the fridge? Check our storage safety guide or speak to a pharmacist.
- Warm pen on arrival? Refrigerate it and contact customer care.
- How to dispose of the pen and needle? Use a sharps bin, then follow your local disposal guidance.
3. Learn how to deal with side effects
Early side effects like nausea, indigestion, constipation, or diarrhoea are common when starting Mounjaro, but they usually settle as your body adjusts, and support is available if you’re struggling or unsure what’s normal.
What to expect in the first few days
Common early symptoms include:
- nausea
- constipation
- diarrhoea
- acid reflux or heartburn
- reduced appetite
- bloating or mild stomach discomfort
For a full overview of early symptoms and what’s normal, see our guide to Mounjaro side effects.
Managing nausea
Nausea is the most common early side effect and often improves after your first few injections. Helpful tips include:
- eating smaller meals
- avoiding large or high-fat foods
- staying upright after eating
- drinking regularly in small sips
Managing constipation or diarrhoea
Constipation and diarrhoea can both occur as your digestive system adapts. These symptoms usually settle quickly and can often be managed with:
- gentle movement
- fibre-rich foods
- staying hydrated
- simple over-the-counter remedies if suitable
For tailored advice, visit our diarrhoea & constipation on Mounjaro guide.
Managing heartburn or acid reflux
Reflux or indigestion can develop from day 1. Simple changes can help, such as:
- avoiding spicy or acidic foods
- eating smaller meals
- not lying down after eating
- limiting caffeine or fizzy drinks
More support is available in our Mounjaro heartburn guide.
If symptoms feel too strong
Side effects are expected to improve with each weekly dose. If you’re still struggling after week 3, you can remain on 2.5mg for an extra month to allow more time for your body to adjust. Speak to your clinician if symptoms are affecting your daily life.
When to seek medical attention
Seek advice if you experience:
- severe vomiting or inability to keep fluids down
- ongoing diarrhoea leading to dehydration
- chest pain or persistent severe reflux
- symptoms that worsen instead of improving
If you’re unsure whether your symptoms are normal, contact a pharmacist, clinician, or NHS 111.
4. Build new, healthy habits
Simple, sustainable habits make your first few weeks on Mounjaro easier and help you get the most from treatment. Focus on gentle changes to your daily routine, including food choices, movement, hydration, sleep, and tracking your progress in a way that feels manageable.
Start with small changes
You don’t need a strict plan. Instead, build a routine that supports your appetite changes and energy levels:
- regular mealtimes
- smaller portions
- lighter meals on injection days
- staying hydrated
- prioritising sleep
If you want meal ideas tailored to early treatment, use our Mounjaro diet plan.
Begin introducing movement
You can start with:
- short walks
- stretching or mobility exercises
- light household activity
Support your nutrition
Alongside balanced meals, some people like to use supplements to support general health. If you’re considering vitamins, our Mounjaro supplements guide explains what may be useful and when to speak to a clinician.
Track your progress
Keeping track of your weight, routine, or goals can help you stay motivated. A simple app or notes on your phone are enough. If you want to understand how your body uses energy, our BMR calculator provides a quick estimate of your daily needs.
5. Know when and how to increase your dose
Most people increase from 2.5mg to 5mg after 4 weeks if they’re tolerating treatment well. Always follow your clinician’s advice before adjusting your dose.
Can I stay on 2.5mg for longer?
Yes. If symptoms haven’t settled, you can stay on 2.5mg for another month to give your body more time to adjust.
What realistic progress looks like in the first few weeks
It’s important to know what to expect when starting 2.5mg of Mounjaro, so you don’t feel discouraged early on. This first dose is used to help your body adjust to the medication, not to drive rapid weight loss straight away.
Some people notice changes in appetite or food cravings before they see changes on the scales. Others may not notice much at all in the first few weeks. Both experiences are normal. Weight loss with Mounjaro is rarely linear, and early plateaus do not mean the treatment isn’t working.
Early progress often shows up in quieter ways, like feeling satisfied with smaller portions, thinking about food less often, or finding it easier to stop eating when you’re full. These changes matter and often set the foundation for more noticeable weight loss as treatment continues.
Tracking progress beyond the scales
The number on the scales is only one way to measure your progress, and it doesn’t always tell the full story, especially early on.
Other signs of progress include looser clothes, higher energy levels, reduced appetite, or simply feeling more in control around food. Noticing these changes can help you stay motivated even when the scales don’t move as quickly as you expected (or want them to!)
It’s also important to remember that weight can fluctuate from week to week due to hydration, digestion, and hormonal changes. Weighing yourself once a week, rather than daily, can help reduce unnecessary stress.
Know when to ask for help
Starting any new treatment means questions, even if everything is going well. You don’t need to wait until something feels “serious” to reach out for help.
You may want to speak to one of our pharmacists or your doctor if:
- side effects feel persistent or are affecting daily life
- you’re unsure about injection timing or missed doses
- you’re worried you’re not eating enough
- you feel anxious about your progress or expectations
Support is there to help you feel safe and confident throughout your treatment. Asking questions early can prevent small concerns from becoming bigger worries.
Don't forget to reorder!
You can reorder your next dose once you’ve completed your first 4 weeks on 2.5mg and you’re tolerating treatment well. Reorder in good time so your next pen arrives before your next injection day.
Make it a bundle if you’re tolerating treatment well
If you’re ready to move to 5mg, you can order a bundle for the next part of your treatment. This helps you stay stocked and reduces the risk of missing a dose.
Frequently asked questions about Mounjaro 2.5mg
How do I dispose of the sharps bin?
Return your full sharps bin using your local council’s collection or drop-off service. Do not place it in household waste.
How do I dispose of the pen and needles?
Used needles and pens go straight into a sharps bin, not household waste.
Can I keep my pen out of the fridge?
Your pen can stay at room temperature (below 30°C) for up to 21 days. Once kept out, do not return it to the fridge.
I’m going on holiday, can I take the pen with me?
Yes. Keep it cool during travel and store it in the fridge on arrival.
The liquid is cloudy, is it safe to use?
No. The liquid should be clear, slightly yellow or colourless. If it looks cloudy or abnormal, do not use it.
There are bubbles in my pen, is this safe to use?
Yes. Small air bubbles are normal and do not affect your injection.
How do I reorder the pen? I need some help deciding which dose to order next.
Reorder through your Chemist4U account. If you’re unsure which dose is next, use our Mounjaro dosing schedule or speak to a clinician.
What if I have injected in the wrong place?
If you injected into the wrong area but still used one of the approved sites, continue as normal. If you’re unsure, contact a clinician for advice.
What side effects are normal?
Mild nausea, reflux, constipation, diarrhoea, reduced appetite, and bloating are common at first. See our Mounjaro side effects page for guidance.
When should I seek medical attention for my side effects?
Seek help if symptoms are severe, getting worse, or you cannot stay hydrated. Contact NHS 111 if you’re unsure.
When will I start to see results?
Some people notice changes in appetite within the first few weeks. However, weight changes vary from person to person, it can take longer.
How do I keep track of my progress?
Use a notes app or a weekly weigh-in. Our BMR calculator can help you understand your energy needs.
Sources
Mounjaro KwikPen 2.5mg solution for injection in pre-filled pen (2025) EMC [accessed 17 November 2025]
Tirzepatide for managing overweight and obesity (2025) NICE [accessed 17 November 2025]
