Mounjaro 12.5mg Injection

The 12.5mg Mounjaro pen is usually prescribed after at least four weeks at 10mg with good tolerability. It can also be used as a temporary step down from 15mg if the higher dose causes uncomfortable side effects. Clinicians may recommend the 12.5mg dose when:

• Weight loss has slowed or plateaued despite continued use of 10mg.
• Appetite suppression has reduced.
• Side effects at lower doses have stabilised.

Each pen contains four once-weekly injections, providing a 4 week course before reassessment.

A Mounjaro 12.5mg pen costs £309 for four weeks, approximately £10.30 per day. Prices can vary slightly depending on your chosen provider and the level of support they offer.

Many patients experience renewed appetite control and progress through weight loss plateaus while on the 12.5mg injection. Potential benefits include:

• Stronger appetite suppression (leading to lower calorie intake)
• Ongoing weight loss, especially visceral fat reduction¹ (the internal fat surrounding your organs that you can’t see)
• Improved metabolic markers, such as fasting glucose and insulin sensitivity²

Common side effects can include:

• Nausea, bloating, or early fullness
• Constipation or diarrhoea
• Mild fatigue or low energy for a few days post-injection

At 12.5 mg, tirzepatide provides enhanced GLP-1 and GIP receptor activation, which helps improve insulin sensitivity and blood-sugar control compared with lower doses².

Even if your weight temporarily stabilises, your body may still be:

• Reducing visceral fat and improving cardiometabolic health¹
• Using insulin more effectively by supporting your pancreas and balancing the hormones that control hunger and fullness³
• Improving cardiovascular markers, such as blood pressure and cholesterol⁴

Real experiences vary widely. Some people find this their ideal maintenance dose, while others move up to 15mg for stronger appetite control under clinician guidance.

“i’m now on the 12.5 dose, I found the worse side effects were on the 4 weeks of 2.5.”

 

“i’m on 12.5 and i’ve lost 7kg since I started”

12.5mg is typically prescribed when you’ve already tried 10mg and need more support with appetite control or weight loss progress. But it can also be a temporary step down from 15mg if side effects are too strong.

You may be ready to increase to 12.5mg if:

• You’ve completed at least four weeks at 10mg.
• Weight loss has plateaued or slowed.
• Your appetite is returning.
• Side effects are minimal and manageable.

You may step down to 12.5mg from 15mg if:

• You’re experiencing strong or persistent side effects (e.g. nausea, fatigue).
• You want to start tapering off Mounjaro when you have reached your goal weight.
• Your clinician recommends temporary dose reduction.

The 12.5mg dose can be powerful – but it also requires a bit more care. Here’s what to avoid at this stage:

• Avoid increasing your dose without guidance. Each step is carefully designed to support your body’s adjustment to the medication.
• Speak to your clinician if side effects persist or feel severe. Don’t try to push through ongoing nausea or fatigue – your clinician can help you adjust or pause safely.
• Keep eating regular, balanced meals and drinking plenty of fluid. Skipping food can make nausea worse and slow your metabolism. Focus on smaller, high-protein meals instead.
• Stay focused on your own progress. Everyone’s journey is different – your results depend on your metabolism, starting point, and lifestyle.

Reaching the 12.5mg injection is a sign of real progress.

Your body has adapted to treatment, and you’re continuing to build healthier habits that support lasting results.

While higher doses can bring stronger effects, they also require balance, so keep communicating with your health coach and clinical team and listen to your body’s signals.

Remember, Mounjaro works best when combined with consistent lifestyle habits, such as regular movement, nutritious meals, good sleep, and self-care. Stay patient, stay supported, and celebrate each step forward.

Dr Jackir Hussain is a GP with over 14 years of experience, having earned his medical degree from the University of Manchester. He has worked across a wide range of primary care settings, including NHS surgeries, unscheduled care services, homeless shelters, and telemedicine. Dr Hussain is passionate about delivering accessible, patient-centred care and helping individuals take practical steps toward improving their health. In his role at Medicspot, he brings a wealth of frontline experience and a calm, compassionate approach to supporting patients on their weight management journey.

Dr Abby Hyams grew up in Manchester and completed her medical training in Bristol. She has been a GP for 19 years, spending many of those as a partner in an NHS practice in Hemel Hempstead. Dr Hyams loves being a GP because of the wide spectrum of people she encounters every day and the opportunity to make a meaningful difference in their lives. She has a particular passion for supporting patients with weight loss and promoting positive behaviour change, helping individuals build sustainable habits that improve their long-term health and wellbeing.

¹ Cariou B, Linge J, Neeland IJ, Dahlqvist Leinhard O, Petersson M, Fernández L et al. Effect of tirzepatide on body fat distribution pattern in people with type 2 diabetes. Last accessed November 2025. [https://pubmed.ncbi.nlm.nih.gov/38528819/]

² Frias JP, De Block C, Brown K, Wang H, Thomas MK, Zeytinoglu M, Maldonado JM. Tirzepatide improved markers of islet cell function and insulin sensitivity in people with type 2 diabetes (SURPASS-2). Last accessed November 2025. [https://pmc.ncbi.nlm.nih.gov/articles/PMC11180500]

³ El Kimberley et al. “The incretin co-agonist tirzepatide requires GIPR for hormone secretion from human islets.” Nature Metabolism. Last accessed November 2025. [https://pubmed.ncbi.nlm.nih.gov/37277609/]

⁴ Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. The New England Journal of Medicine. Last accessed November 2025. [https://www.nejm.org/doi/full/10.1056/NEJMoa2206038]

Eli Lilly and Company Ltd. “Mounjaro® KwikPen 12.5 mg solution for injection in pre-filled pen – Summary of Product Characteristics (SmPC).” Electronic Medicines Compendium (eMC). Last accessed November 2025. [https://www.medicines.org.uk/emc/product/15485/smpc]

Diabetes UK. Mounjaro (tirzepatide) – uses, how it works and side effects. Last accessed November 2025. [https://www.diabetes.org.uk/about-diabetes/looking-after-diabetes/treatments/tablets-and-medication/glp-1/mounjaro]

This article is for general information only and should not be used for the diagnosis or treatment of medical conditions. Medic Spot Limited has used all reasonable care in compiling the information but makes no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. In the event of an emergency, please call 999 for immediate assistance.

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