Mounjaro (Tirzepatide) Injections

Mounjaro is a prescription-only, once-weekly injection that may be prescribed to support weight loss and long-term weight management in adults who meet the clinical eligibility criteria. The active ingredient in Mounjaro is tirzepatide.

Tirzepatide works by targeting two hormone pathways involved in appetite and metabolism: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). By acting on both, Mounjaro can help reduce appetite, increase feelings of fullness, and support healthier eating habits.

Mounjaro is only available following a clinician review to confirm it is suitable and safe based on your health information. If approved, it is supplied and dispensed by our UK GPhC-registered pharmacy and delivered securely and discreetly to your doo.

Mounjaro works by mimicking the effects of two naturally occurring hormones involved in appetite regulation and blood sugar control: GLP-1 and GIP. By acting on both pathways, it helps address hunger and eating behaviour in a more comprehensive way than treatments that target GLP-1 alone.

Mounjaro supports weight loss in several key ways:

• Reduces appetite by signalling to the brain that you feel full, helping to curb hunger and cravings
  
• Increases feelings of fullness after meals, making it easier to eat smaller portions
  
• Slows digestion, which helps you feel satisfied for longer between meals
  
• Helps regulate blood sugar levels, reducing spikes and dips that can trigger hunger
  

Together, these effects can make it easier to maintain a calorie deficit when combined with healthy eating and physical activity, supporting steady and sustainable weight loss.For practical food guidance, see our what to eat while using weight-loss injections guide.

Clinical studies have shown Mounjaro to be an effective treatment for supporting weight loss when used alongside healthy lifestyle changes, such as a balanced diet and regular physical activity. Results can vary between individuals, but many people experience meaningful and sustained weight loss over time.

In large clinical trials involving adults with overweight or obesity, participants using tirzepatide achieved average weight loss of up to around 22.5% of their starting body weight over a treatment period of approximately 72 weeks. These results were generally greater than those seen with treatments that target GLP-1 alone.

The level of weight loss achieved can depend on several factors, including:

• Your starting weight and body composition
  
• The dose prescribed and how your body responds to treatment
  
• Adherence to dietary and lifestyle guidance
  
• Underlying health conditions and metabolism
  

It’s important to note that weight loss with Mounjaro is typically gradual and progressive, rather than rapid. This steady approach supports safer, more sustainable results and can help with long-term weight management when treatment is continued under clinical supervision.

The figures in the table below are based on average outcomes observed in clinical studies and are provided for general guidance only. Individual results may vary, and not everyone will reach the highest doses shown.

Most people start on a low dose and increase gradually to minimise side effects. Some patients achieve good results on lower doses and do not need to increase further.

Weight loss with Mounjaro is typically gradual and progressive. While individual experiences vary, most people notice changes in appetite first, followed by more visible weight loss as treatment continues and doses are adjusted under clinical supervision.

For a more detailed breakdown of expected changes by week and dose, see our Mounjaro weight-loss timeline and results guide.

Mounjaro may be suitable for adults who meet specific clinical criteria. Eligibility is based on your BMI, medical history, and overall health, and is assessed during your online consultation.

Mounjaro is not suitable for everyone. During your online consultation, our clinicians carefully assess your medical history to ensure treatment is safe and appropriate. You may not be suitable for Mounjaro if any of the following apply.

Mounjaro may affect how other medications are absorbed, especially oral drugs. Discuss all current medications with your Happy Pharmacy online pharmacist during your consultation.

Most people start Mounjaro on a low dose, which allows the body time to adjust to treatment and helps reduce the likelihood of side effects such as nausea. This initial phase is important for building tolerance before any dose increases are considered.

Over time, the dose may be increased gradually, usually in step-by-step stages, depending on how your body responds. Some people see good appetite control and weight-loss results on lower doses and do not need to increase further, while others may benefit from higher doses. Dose changes are always guided by your individual response and tolerability.

Your Mounjaro dosage is clinician-led and reviewed throughout treatment. During your online check-ins, your prescriber will assess progress, side effects, and overall suitability to determine whether to maintain, increase, or pause your current dose. This personalised approach helps ensure treatment remains safe, effective, and appropriate for long-term use.

Mounjaro is supplied as an easy-to-use, pre-filled injection pen. It is injected once weekly, on the same day each week where possible. Always use a new needle for each injection and rotate injection sites to help reduce skin irritation. Mounjaro can be taken with or without food, making it easy to fit into your weekly routine.

For full manufacturer instructions, read our how to use the Mounjaro injection pen guide.

Mounjaro should be injected into the fatty tissue of the abdomen or upper thigh. Avoid injecting into the same spot each time. The upper arm may also be used if the injection is being given by someone else.

Many people are initially concerned about self-injection, but Mounjaro's KwikiPen makes the process simple and nearly pain-free. The pen is designed for ease of use at home and comes with clear step-by-step instructions.Your prescriber and pharmacist are available if you need guidance at any stage.

Like all prescription medicines, Mounjaro can cause side effects, although not everyone will experience them. Most side effects are mild to moderate, occur early in treatment, and often improve as your body adjusts to the medication.

Side effects are more likely when starting treatment or after a dose increase. This is why Mounjaro is typically started at a low dose and increased gradually under clinical supervision. If you would like to compare side effects across different weight-loss injections, see our weight-loss injection side effects guide.

The table below outlines common side effects that are usually manageable at home, as well as less common but more serious symptoms that require medical advice.

Side effects are most common when starting Mounjaro or increasing your dose. Most are mild and improve as your body adjusts. The guidance below covers practical ways to manage common symptoms and when to seek medical advice.

Most people experience only mild digestive symptoms that settle within a few weeks, particularly when doses are increased gradually.

Mild redness, itching, bruising or tenderness around the injection site can happen, particularly early on. Rotating injection sites and using good technique usually helps.

• Rotate the site each week
  
• Let the pen warm to room temperature if stored in the fridge (do not heat)
  
• Avoid injecting into irritated, bruised, scarred or inflamed skin
  
• Seek advice if the reaction spreads, becomes very painful, or you develop hives/swelling

If side effects are troublesome, your prescriber may recommend staying on your current dose for longer before increasing. Do not change your dose without clinician advice.

If you experience side effects that are persistent, worsening, or affecting your day-to-day life, our clinical team is here to help. We can provide guidance on managing symptoms, advise on dose adjustments, and assess whether ongoing treatment remains appropriate for you.

You can contact Happy Pharmacy at any point during treatment if you have concerns about side effects, dosing, or how your body is responding to Mounjaro. Our GPhC-registered pharmacists and prescribers will review your symptoms and advise on next steps.

If you feel very unwell or develop severe symptoms, seek urgent medical advice via NHS 111 or A&E.

Wegovy (semaglutide) is an alternative to Mounjaro. This also uses GLP-1 receptor agonists to promote weight loss. Your Happy Pharmacy online pharmacist can help decide which is best for you.

While both Mounjaro and Wegovy are weight loss injections, Mounjaro targets two hormones (GLP-1 and GIP), while Wegovy only targets GLP-1. This dual action may make Mounjaro more effective for some patients. Both are prescription weight loss treatments.