Tirzepatide Explained

Tirzepatide is a new kind of treatment that has gained major attention for its ability to support both blood-sugar control and substantial weight loss. It is the active ingredient in Mounjaro and Zepbound, two medications developed by Eli Lilly.

What makes tirzepatide different is that it acts on two hormones instead of one. It targets the same GLP-1 pathway as semaglutide but also activates another hormone system called GIP. These two signals work together to control appetite, metabolism, and energy use.

For people struggling with weight loss, tirzepatide represents the next step forward after semaglutide. It builds on everything doctors have learned from GLP-1 treatments but adds an extra mechanism that seems to enhance results even further.

This article explains what tirzepatide is, how it works, what the research shows, who it is for, and what you should know before considering treatment.

Tirzepatide is a dual incretin medication. That means it mimics the effects of two natural hormones your body releases after eating:

• GLP-1 (glucagon-like peptide-1)
• GIP (glucose-dependent insulinotropic polypeptide)

Both hormones help regulate appetite, digestion, and insulin production. Scientists discovered that combining their actions into a single medicine could help improve both blood-sugar control and weight management more effectively than targeting one hormone alone.

In simple terms, tirzepatide helps the body eat less, store less, and burn energy more efficiently. Think of it as recalibrating the body’s hunger and metabolism controls so they work the way they should.

Tirzepatide is available as a once-weekly injection and is the active ingredient in Mounjaro (approved in the UK for weight management and type 2 diabetes) and Zepbound (approved in the US for chronic weight management).

To understand tirzepatide, imagine two messaging systems in your body that help coordinate eating and energy use. GLP-1 and GIP are those messengers. They tell your brain when you are full, guide your pancreas to release insulin, and influence how your body stores or burns calories.

Tirzepatide acts as a dual receptor agonist, meaning it activates both sets of signals:

1. GLP-1 pathway: Reduces hunger, slows stomach emptying, and promotes insulin release after meals.
2. GIP pathway: Enhances insulin sensitivity and helps fine-tune how your body uses energy.

When these two systems are stimulated together, the effects appear to reinforce each other. The result is stronger appetite control, improved blood-sugar regulation, and significant fat reduction over time.

Essentially, tirzepatide helps reset your body’s energy balance. The upshot is that you feel fuller sooner, experience fewer cravings, and naturally consume fewer calories without relying on willpower alone allowing you to develop long lasting habits that will help maintain your weight loss into the future.

Tirzepatide’s approval is based on extensive clinical research through two global trial programmes: SURPASS for diabetes and SURMOUNT for weight management.

Diabetes outcomes (SURPASS trials)

• SURPASS-2 (NEJM 2021): Compared tirzepatide with semaglutide 1 mg. Tirzepatide produced greater reductions in blood sugar (HbA1c drop of -2.3% vs -1.9%) and weight (-12 kg vs -6 kg) over a 40 week period.

• SURPASS-4 (Lancet 2021): Demonstrated better blood sugar control compared to long acting insulin with no increased risk of heart problems. This confirmed Tirzepatide was safe to use for diabetes without increasing the risk of heart attacks or strokes. 

Weight management outcomes (SURMOUNT trials)

• SURMOUNT-1 (NEJM 2022): Reported an average 21% body-weight reduction over 72 weeks in adults with obesity or overweight who were given 15mg Tirzepatide compared to 3% for people who were given placebo. .

• SURMOUNT-3 and SURMOUNT-4: Showed that weight loss Tirzepatide was effective as helping people lose weight but when it was stopped people often put the weight back on. Staying on it longer term and giving lifestyle advice helped people to maintain their weight loss. 

Across these trials, tirzepatide delivered some of the best results seen in weight loss and diabetic control for once weekly injectoble medication, 

What this means for patients is that tirzepatide can help the body achieve and maintain significant fat loss while improving overall metabolic health, blood pressure, and cholesterol.

In the United Kingdom and European Union, tirzepatide (Mounjaro) is approved for:

• Treatment of type 2 diabetes mellitus in adults when other medication have not helped with blood sugar enough or not been tolerated due to side effects, or if your job means you cant take  medication which can give you hypoglycaemia (your sugar going too low) and your health would benefit from losing weight. 

It is also approved by the MHRA and NICE for chronic weight management, as Mounjaro in the UK.

Eligibility includes:

• A body mass index (BMI) of 30 or higher
• Or a BMI of 27 or higher with a related condition such as high blood pressure, high cholesterol, or sleep apnoea

Tirzepatide should not be used in pregnancy, during breastfeeding, or by anyone with a history of certain endocrine or pancreatic conditions. Treatment should always be prescribed and monitored by a qualified healthcare professional.

Although both brands contain the same active ingredient, they differ in their approvals and market availability.

Mounjaro

• Form: Weekly injection

• Typical dose range: 2.5 mg to 15 mg

• Primary use: Type 2 diabetes (also used for weight management both in the NHS and privately)

• UK availability: Available privately and on the NHS for certain groups of people

Zepbound

• Form: Weekly injection

• Typical dose range: 2.5 mg to 15 mg

• Primary use: Chronic weight management (FDA-approved in the US)

• UK availability: Not currently available in the UK

Both medicines are supplied as pre-filled pens for once-weekly subcutaneous injection. Treatment usually starts at 2.5 mg weekly and increases gradually to help minimise side effects.

Tirzepatide’s safety profile is similar to that of other GLP-1 medicines, though gastrointestinal effects are slightly more common during dose escalation.

Common side effects:

• Nausea or vomiting
• Diarrhoea or constipation
• Fatigue or lightheadedness
• Reduced appetite

Less common:

• Injection-site irritation and bruising
• Bloating or abdominal discomfort

Serious but rare:

• Pancreatitis (inflammation of the pancreas)
• Gallbladder disease
• Possible thyroid C-cell changes observed in animal studies, not confirmed in humans
• Injection site injection

Tirzepatide should not be used by anyone with:

• A personal or family history of medullary thyroid carcinoma or MEN2 syndrome
• A history of pancreatitis
• Severe gastrointestinal disease

Always contact your prescriber if you experience persistent abdominal pain or symptoms of dehydration. As with semaglutide, these side effects often improve over time as your body adjusts.

Tirzepatide belongs to a newer class of treatments sometimes called twincretins because they act on both GLP-1 and GIP receptors.

When compared with semaglutide, tirzepatide tends to:

• Produce greater average weight loss (around 22% vs 15%)
• Achieve equal or better blood-sugar reduction
• Possibly boost energy use through the added GIP mechanism

This dual effect helps explain why tirzepatide often produces faster and deeper results in clinical studies. However, both medicines remain highly effective and safe when prescribed appropriately.

Research and real-world evidence consistently show that tirzepatide delivers profound improvements in both body composition and metabolic health. Typical outcomes after 12 to 18 months can include:

• 15–22% average body-weight reduction
• Significant decrease in waist circumference and visceral fat
• Improved insulin sensitivity and beta-cell function
• Reduced triglycerides, inflammatory blood markers, and systolic blood pressure

In simple terms, tirzepatide not only supports weight loss but also helps restore a healthier metabolism, improving how the body manages blood sugar and energy long term.

Tirzepatide continues to be studied in a wide range of clinical settings, including:

• Cardiovascular risk reduction in people without diabetes
• Non-alcoholic fatty liver disease (NASH)
• Combination therapy with SGLT-2 inhibitors

Ongoing studies such as SURPASS-CVOT and SURMOUNT-MMO are expected to clarify its long-term benefits in preventing metabolic disease, improving heart health and decreasing mortality in people with obesity.

Tirzepatide is a prescription-only medication regulated by the MHRA in the UK. It is available through the NHS for type 2 diabetes and people with obesity who fit certain criteria. It is also available privately for eligible adults seeking weight management support.

Medicspot provides access to tirzepatide treatment (Mounjaro) through a supervised clinical assessment in line with NICE guidance. This ensures the medication is used safely and responsibly.

If you are considering tirzepatide, the first step is to complete a consultation with a licensed prescriber who can review your health history and treatment goals.

Starting tirzepatide can take some adjustment, but a few habits make the process smoother:

• Eat slowly and stop when you feel comfortably full
• Stay hydrated and avoid skipping meals
• Choose lighter, balanced foods while your body adapts
• Limit alcohol during dose increases
• Prioritise rest, gentle movement, and consistency
• Track progress weekly rather than daily

1. Frias JP et al. NEJM 2021 – SURPASS-2 trial
2. Jastreboff AM et al. NEJM 2022 – SURMOUNT-1 trial
3. Rosenstock J et al. Lancet 2021 – SURPASS-1 trial
4. Lilly Clinical Trial Registry – SURPASS and SURMOUNT programmes
5. EMA Assessment Report for Mounjaro (tirzepatide) 2023
6. NICE, Obesity: identification, assessment, and management, NG248 (2023)

Dr Adam Abbs is a GP and Medical Lead for Europe and UK for biomarker company Hurdle. An NHS-trained GP, he graduated from Hull York Medical School in 2010 with an MBBS, then worked across a range of specialties in Newcastle and Manchester. Dr Adam Abbs is SCOPE certified (the international gold standard for obesity management) and has a keen focus on personalised medicine and weight loss. He authored Medicspot’s Behaviour Change Course.

Dr Abby Hyams completed her medical training in Bristol and has been a GP for 19 years, spending many of those as a partner in an NHS practice in Hemel Hempstead. 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.

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 healthcare professional for diagnosis and treatment of medical conditions. In the event of an emergency, please call 999 for immediate assistance.

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