Mounjaro quick guide – the basics in two minutes

Robert Price | Last update: 19th January 2026

So first up, what’s SlimrChat?

We’re a community site for people considering using prescription weight loss treatments, like Mounjaro, as part of their weight loss journey. Or those who have used them and are in the weight maintenance stage, or people who are just interested. 

We’re not a medical site, we don’t sell any medication, and we never will.

The basics

Mounjaro is a prescription only medication licensed in the UK for weight management and for the treatment of type 2 diabetes. 

It is taken as a once-weekly self-injection and is designed to support significant weight loss when used alongside a reduced calorie diet and regular physical activity. Mounjaro should always be part of an overall weight loss plan.

This is a guide intended to explain how Mounjaro works, who it may be suitable for and what to expect if you’re considering it. Availability, eligibility and pricing can change and this article will be updated regularly.

What is Mounjaro and how does it work?

The active ingredient in Mounjaro is tirzepatide. It belongs to a newer class of treatments known as dual-agonist weight loss medications.

Mounjaro mimics two naturally occurring gut hormones involved in appetite and blood-sugar control:

• GLP-1 (glucagon-like peptide-1)
  Helps regulate blood glucose, slows digestion and signals fullness to the brain, reducing hunger and cravings.
• GIP (glucose-dependent insulinotropic polypeptide)
  Works alongside GLP-1 to improve insulin response and energy balance, enhancing appetite suppression.
  

By slowing gastric emptying (how quickly food leaves the stomach) and influencing appetite signals in the brain, Mounjaro helps many people feel fuller sooner and for longer, making it easier to reduce calorie intake.

How effective is Mounjaro for weight loss?

Clinical trials have shown Mounjaro to be one of the most effective weight-loss treatments currently available.

• In large studies, people taking the highest maintenance dose (15mg) lost up to 22.5% of their starting body weight over around 72 weeks.
• This compares with average losses of around 14–15% reported in similar trials of single-hormone injections such as Wegovy / Ozempic.
  

Results vary from person to person. Weight loss tends to be gradual, with the most noticeable changes occurring once people reach their maintenance dose and have adjusted to treatment.

Of course, you won’t be surprised that if you return to the same behaviours you had before your weight loss drug journey you will gain weight after stopping use of Mounjaro. That’s why your maintenance plan is vital. We’re here to help with that too.

Who is eligible for Mounjaro in the UK?

Eligibility depends on whether Mounjaro is accessed privately or via the NHS.

Private prescription

You may be eligible through a private clinic or pharmacy-led service if you have:

• A BMI of 30 or above (classified as obese), or
  
• A BMI of 27 or above with at least one weight-related health condition, such as:
  
  • High blood pressure
    
  • High cholesterol
    
  • Prediabetes or type 2 diabetes
    

Private providers, including online pharmacies, have to ensure they follow the health regulations and usually require an online consultation and medical screening.

NHS access

NHS access is currently limited and phased, prioritising people with the highest clinical need.

At present, this typically includes:

• A BMI of 40 or above (or 37.5 for some ethnic backgrounds), and
  
• Multiple weight-related health conditions, often four or more (such as type 2 diabetes, cardiovascular disease, hypertension, or sleep apnoea).
  

Local eligibility criteria and waiting times can vary significantly across the UK.

How is Mounjaro taken?

In the UK Mounjaro is most commonly supplied as the Mounjaro KwikPen. This a multi-dose syringe pen containing four weekly doses. The KwikPen is really straightforward to use.

Dosing schedule

• Treatment usually starts at 2.5mg once weekly for the first four weeks.
  
• The dose may then be increased in 2.5mg steps every four weeks, depending on tolerance and response.
  
• The maximum maintenance dose is 15mg once weekly.
  

The gradual increase is designed to reduce side effects and help your body adjust.

Injecting Mounjaro

• Mounjaro is injected once a week on the same day, with or without food.
  
• Common injection sites include the abdomen (tummy), thigh or upper arm.
  
• Injection sites should be rotated weekly to reduce skin irritation.

Common side effects

Side effects are most common when starting treatment or increasing the dose. For many of our community these improve over time.

Digestive side effects

• Nausea or vomiting
  
• Diarrhoea or constipation
  
• Indigestion, bloating or wind
  
• Abdominal discomfort or pain
  

Other side effects

• Fatigue or low energy
  
• Dizziness or light-headedness
  
• Temporary hair thinning or hair loss
  
• Mild injection-site reactions (redness, itching, bruising)
  

Rare but serious risks

Serious side effects are uncommon but can include pancreatitis (severe, persistent abdominal pain) and severe allergic reactions. You should seek urgent medical help if these occur.

Important safety information

• Pregnancy and breastfeeding
  Mounjaro must not be used during pregnancy, while trying to conceive, or when breastfeeding.
• Oral contraception
  Mounjaro can reduce the effectiveness of the contraceptive pill, particularly when starting treatment or increasing doses. UK guidance advises using a barrier method (e.g. condoms) for four weeks after starting and four weeks after each dose increase.
• Alcohol
  There is no direct interaction, but alcohol is high in calories and may worsen side effects such as nausea or low blood sugar, potentially slowing progress.

How much does Mounjaro cost in the UK?

NHS prescription:
You pay the standard NHS prescription charge of £9.90, if eligible.

Private prescription: prices vary by provider and dose. As a general guide prices for each pen start at:

• • 2.5mg starter pen £135
  • 5.0mg £150
  • 7.5mg pen £200
  • 10mg £230
  • 12.5mg £240
  • 15mg £260
    

Prices, availability and support packages differ between pharmacies, so it’s worth comparing providers carefully. We’ll be launching a live pricing comparison service and pharmacy guide in February.

Key takeaway

Mounjaro represents a significant development in medical weight management, offering greater average weight loss than earlier injections for many people. However, it is not a quick fix and works best when combined with long-term lifestyle changes and appropriate medical support.

 

For more info look at how it’s not the easy way out, safety of weight loss drugs, getting weight loss drug prescriptions and are weight loss drugs right for you?