“I’ve been prescribed Mounjaro, but I’m not sure how to use the pen.”
“Do I take it with food, or does it matter what time of day?”
“What happens if I forget my weekly injection?”
If you’ve been prescribed a weekly weight loss injection, knowing how to use it confidently makes a real difference to how well it works and how comfortable you feel along the way. The pens are designed to be straightforward, and most people settle into a simple weekly routine within the first few weeks.
In this guide, we’ll cover the two medications prescribed for weight management at Summerhill Health, Mounjaro (tirzepatide) and Wegovy (semaglutide), with practical advice on dosing, injection technique, timing, missed doses, side effects, and storage. For eligibility, blood tests, pricing, and what your appointments entail, please refer to our weight loss injections service.
At Summerhill Health, Dr Natalie Summerhill prescribes weight loss injections within NICE, RCGP, and current GMC guidance, with every treatment plan built around your medical history, your goals, and how your body responds. Treatment is always grounded in an in-person assessment and baseline blood monitoring.
Please note: This guide provides general information only. Always follow the specific instructions given by Dr Summerhill and the patient information leaflet that comes with your pen, and contact us if you’re unsure about anything.
How Weight Loss Injections Work
Mounjaro and Wegovy are once-weekly injections that act on gut hormone pathways to reduce appetite, slow how quickly the stomach empties, and improve how the body handles blood sugar. The practical effect for most people is feeling fuller sooner, staying satisfied for longer, and noticing fewer food cravings.
Both medications work best when the dose is built up gradually. Starting low and increasing in steps gives your body time to adjust and keeps side effects to a minimum. This is why the first few months follow a set titration schedule rather than going straight to a full dose.
They are a medical treatment, so please do not mistake them for a quick fix. They work alongside the changes you make to how you eat, move, sleep, and manage stress. We build that wider support into every review.
How to Take Mounjaro
Mounjaro (the brand name for tirzepatide) is given as a once-weekly injection under the skin, on the same day each week. You can take it at any time of day, with or without food.
- The usual starting dose is 2.5mg once weekly for the first 4 weeks. This is a starting dose to help your body adjust, not a treatment dose.
- After 4 weeks, the dose usually increases to 5mg once weekly.
- From there, the dose can be increased in 2.5mg steps, with at least 4 weeks at each dose before moving up.
- Maintenance doses are typically 5mg, 10mg, or 15mg, and the maximum dose is 15mg once weekly.
Dr Summerhill will guide each step up based on your progress, how you’re tolerating treatment, and your blood results. There is no benefit to rushing the titration, and staying a little longer at a given dose is sometimes the more comfortable route.
How to Take Wegovy
Wegovy (the brand name for semaglutide licensed for weight management) is also a once-weekly injection under the skin, on the same day each week, at any time of day, with or without food.
Wegovy follows a monthly step-up schedule:
- Weeks 1 to 4: 0.25mg once weekly
- Weeks 5 to 8: 0.5mg once weekly
- Weeks 9 to 12: 1mg once weekly
- Weeks 13 to 16: 1.7mg once weekly
- Week 17 onwards: 2.4mg once weekly (the maintenance dose)
The maximum dose is 2.4mg once weekly. If a particular step-up causes troublesome side effects, Dr Summerhill may keep you at your current dose for longer or adjust the plan to suit you. The goal is steady, sustainable progress, not the fastest possible escalation.
Comparing Mounjaro and Wegovy Dosing
There is no single “best” option. The right choice depends on your medical history, how you tolerate treatment, your goals, and current supply. Dr Summerhill will talk you through the differences and recommend the option likely to suit you best.
| Feature | Mounjaro (tirzepatide) | Wegovy (semaglutide) |
|---|---|---|
| How it’s given | Once-weekly injection | Once-weekly injection |
| Starting dose | 2.5mg weekly for 4 weeks | 0.25mg weekly for 4 weeks |
| How the dose builds | In 2.5mg steps, at least 4 weeks apart | Set monthly steps: 0.25 to 0.5 to 1 to 1.7 to 2.4mg |
| Usual maintenance dose | 5mg, 10mg, or 15mg | 2.4mg |
| Maximum dose | 15mg weekly | 2.4mg weekly |
| Timing | Any time of day, with or without food | Any time of day, with or without food |
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How to Use Your Injection Pen
Most patients self-administer at home, and we’ll show you exactly how during your treatment start consultation. If you’d rather not inject yourself, we can give your injection in clinic. Here is the general approach for a pre-filled pen:
- Wash your hands with soap and water.
- Check the pen. Confirm the medication name and dose, check the expiry date, and look at the liquid. It should be clear and colourless to slightly yellow. Do not use it if it looks cloudy or contains particles.
- Choose your injection site. The abdomen (keeping a few centimetres away from your belly button), the front of your thighs, or the back of your upper arms all work well.
- Rotate the site each week. Using a different spot each time reduces soreness and skin changes. If you stay in one area, such as the abdomen, move to a slightly different point within it each week.
- Clean the skin if advised, and let it dry.
- Inject as instructed. Most pens are pressed against the skin and held in place until the dose finishes. Hold the pen in place and count to 6 (or follow the specific count specified for your pen) to ensure the full dose has been delivered safely.
- Dispose of the pen or needle safely in a sharps bin. Never put needles in your household waste.
Top tip: Pick a consistent weekly slot, such as a Sunday evening, and set a phone reminder. A steady routine is the easiest way to stay on track.
Choosing Your Injection Day
Pick a day that fits your week and stick to it. Injecting on the same day each week keeps the medication level steady in your system. The time of day does not matter, so choose whatever you’ll remember most reliably.
If you need to move your regular day, you can usually do so as long as your last dose was at least 3 days (72 hours) ago. Check with us if you’re unsure.
What to Do If You Miss a Dose
Missing the occasional dose happens. Here is the general guidance, though always check your patient information leaflet:
- Mounjaro: If you miss a dose, take it as soon as possible within 4 days (96 hours) of the missed dose. If more than 4 days have passed, skip it and take your next dose on your usual day.
- Wegovy: If your next scheduled dose is more than 2 days (48 hours) away, take the missed dose as soon as you remember. If it’s less than 2 days away, skip it and carry on as normal.
Never take two doses close together to make up for a missed one. If you’ve missed several weeks in a row, get in touch before restarting, as you may need to step back down to a lower dose.
Managing Side Effects
Most people tolerate these medications well, especially when the dose is built up slowly. The most common effects appear in the early weeks and after each dose increase, and usually settle as your body adjusts. A few practical steps help:
- Nausea: Eat smaller portions, stop when you feel full, and favour plain, lighter meals. Greasy, rich, or very large meals tend to make it worse.
- Reflux or indigestion: Avoid lying down straight after eating, and keep evening meals lighter.
- Constipation: Increase fibre gradually, stay well hydrated, and keep moving. A gentle daily walk helps.
- Loose stools: Keep your fluids up, particularly if symptoms last more than a day or two.
- Fatigue or headaches: These often ease within the first few weeks. Eating regularly and staying hydrated makes a difference, as appetite drops can sometimes mean you’re eating or drinking less than you realise.
If side effects are troublesome and aren’t settling, contact us before your next dose increase. Slowing the titration is often all that’s needed.
Seek urgent medical advice if you experience severe or persistent abdominal pain (especially pain that spreads to your back), repeated vomiting, signs of dehydration, or any reaction such as swelling, a rash, or difficulty breathing. These are uncommon but need prompt assessment.
Eating Well While on Treatment
Because your appetite will be lower, it’s worth making the food you do eat count:
- Prioritise protein and calcium at each meal to help protect muscle and bone as you lose weight.
- Include fruit, vegetables, and fibre to support digestion and keep you satisfied.
- Stay hydrated, as it’s easy to drink less when you’re less hungry.
- Limit alcohol, which adds empty calories and can worsen nausea.
These habits are what make results last. The injection reduces appetite, but the changes you build around it are what carry you through long term.
Photo by freestocks on Unsplash
How to Store Your Medication
- Before first use: Keep your pens in the fridge (2°C to 8°C). Do not freeze, and do not use a pen that has been frozen.
- In use or travelling: Both Mounjaro and Wegovy pens can be kept at room temperature for a limited period (Mounjaro below 30°C for up to 30 days; Wegovy below 30°C for up to 28 days). Check the leaflet for your specific pen and do not return a pen to the fridge once it’s been kept at room temperature beyond the stated window.
- Keep pens in the original carton to protect them from light, and store all medication out of reach of children.
- Do not use any pen past its expiry date.
Frequently Asked Questions
Does it matter what time of day I inject?
No. Both Mounjaro and Wegovy can be taken at any time of day, with or without food. Consistency of day matters more than time, so pick a slot you’ll remember each week.
Can I switch my injection day?
Yes, as long as your most recent dose was at least 3 days (72 hours) ago. After switching, continue on your new chosen day each week.
Can I drink alcohol while on treatment?
Alcohol isn’t forbidden, but it adds calories, can worsen nausea, and works against your goals. Keeping it to a minimum will help both your comfort and your results.
Will the injection work on its own?
It does the heavy lifting on appetite, but lasting results come from pairing it with sustainable changes to how you eat, move, sleep, and manage stress. We support you with this at every review.
What if I can’t face injecting myself?
That’s completely understandable. We can give your weekly injection in clinic if you’d prefer, so needle anxiety or a preference for clinical oversight is never a barrier to treatment.
How soon should I expect results?
Most people notice their appetite change within the first one to two weeks, with visible weight loss following over the first one to three months as the dose builds. We’ll review your progress at each follow-up and adjust your plan as needed.
When to Contact the Clinic
Get in touch if:
- Side effects are troublesome or aren’t settling before your next dose increase.
- You’ve missed several doses and aren’t sure how to restart.
- Your appetite or weight isn’t responding as expected.
- You have any questions or concerns about your treatment.
Seek urgent medical advice if you have severe or persistent abdominal pain, repeated vomiting, signs of dehydration, or any sign of a serious allergic reaction such as swelling, rash, or difficulty breathing. These are rare but need immediate assessment.
Ready to Take the Next Step?
If you’re considering weight loss injections, or you have questions about treatment you’ve already started, our team at Summerhill Health is here to help. Our consultations are thorough, confidential, and unhurried, with same-day and evening appointments available.
Contact us on 0161 552 2382 or book an appointment online.
