Tirzepatide (Mounjaro)
Is It Right for You?
A complete guide to Tirzepatide (Mounjaro) — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Tirzepatide (Mounjaro)?
Tirzepatide, marketed under the brand name Mounjaro, is a novel injectable medication belonging to a new class of drugs known as dual GIP/GLP-1 receptor agonists. It simultaneously activates two gut hormone receptors — the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor — making it the first of its kind and distinguishing it from existing GLP-1-only medications such as semaglutide (Ozempic/Wegovy).
Mounjaro is administered as a once-weekly subcutaneous injection, available in pre-filled, ready-to-use auto-injector pens in doses of 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg. It was licensed in the UK for the treatment of type 2 diabetes mellitus in 2023, with a subsequent licence for chronic weight management in adults living with obesity (BMI ≥30 kg/m²) or overweight (BMI ≥27 kg/m²) with at least one weight-related comorbidity.
Clinical trial data (the SURMOUNT programme) have demonstrated that tirzepatide produces some of the most substantial weight loss results ever recorded for a pharmaceutical agent — participants lost an average of 20–22% of total body weight at the highest doses, exceeding the outcomes achieved with previously available treatments. This has positioned Mounjaro as a landmark medication in the management of obesity and metabolic disease.
Tirzepatide (Mounjaro) is a prescription-only medication. A licensed clinician must assess your eligibility, medical history, and suitability before prescribing.
What Conditions Is Tirzepatide Used For?
Tirzepatide is licensed for:
to improve glycaemic (blood sugar) control in adults, used as monotherapy or in combination with other antidiabetic medications. Tirzepatide consistently produces superior HbA1c reductions compared with all other available non-insulin diabetes treatments.
in adults with a BMI of ≥30 kg/m², or ≥27 kg/m² with at least one weight-related comorbidity (such as type 2 diabetes, hypertension, obstructive sleep apnoea, dyslipidaemia, or cardiovascular disease), alongside a reduced-calorie diet and increased physical activity.
Tirzepatide is not licensed for use in type 1 diabetes mellitus. It is also not a substitute for insulin in patients who require insulin therapy. It has no direct effect on insulin production in the context of absolute insulin deficiency.
How Does Tirzepatide Work?
Tirzepatide is a single molecule that acts as an agonist at both the GIP receptor and the GLP-1 receptor — two receptors that play important roles in regulating blood glucose, appetite, energy balance, and metabolic function.
GLP-1 receptor agonism — GLP-1 is a hormone released from the gut after eating. It stimulates glucose-dependent insulin secretion (insulin is released only when blood glucose is elevated, reducing the risk of hypoglycaemia), suppresses glucagon release, slows gastric emptying (prolonging satiety), and acts on hypothalamic centres in the brain to reduce appetite and food intake. These are the same mechanisms exploited by semaglutide and liraglutide.
GIP receptor agonism — GIP is another incretin hormone released postprandially. It potentiates insulin secretion, has direct effects on fat tissue metabolism, and — critically — appears to enhance the weight-loss and metabolic effects of GLP-1 receptor agonism when the two pathways are activated simultaneously. The combination of GIP and GLP-1 agonism produces greater reductions in appetite, food intake, and body weight than GLP-1 agonism alone.
The net effect is a powerful reduction in blood glucose, a substantial decrease in appetite and caloric intake, slowing of gastric emptying, and — with sustained treatment — significant and progressive loss of body fat. These effects are dose-dependent, with greater weight loss and glycaemic benefits seen at higher doses.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Administer once weekly, on the same day each week, at any time of day regardless of meals. If you change your injection day, ensure at least 3 days separate doses during the transition.
Inject subcutaneously into the abdomen, upper thigh, or upper arm. Rotate injection sites with each dose to avoid tissue reactions.
The auto-injector pen is single-use. Do not reuse pens. After use, dispose of in an approved sharps container.
Store pens in a refrigerator (2–8°C). Pens can be stored at room temperature (below 30°C) for up to 21 days if needed. Do not freeze. Protect from light.
Allow the pen to reach room temperature for approximately 30 minutes before injecting to reduce injection site discomfort.
Do not skip doses — consistency is important for both glycaemic control and weight management outcomes.
Side Effects of Tirzepatide
Side effects are most common during dose escalation and typically improve with time.
- Nausea (very common, particularly on initiation and dose escalation)
- Vomiting
- Diarrhoea
- Constipation
- Abdominal pain or bloating
- Decreased appetite
- Injection site reactions
- Acute pancreatitis — severe persistent abdominal pain; discontinue and seek emergency care immediately.
Cases of acute pancreatitis have been reported with GLP-1 receptor agonists. Discontinue tirzepatide immediately if pancreatitis is suspected.
Drug Interactions
Tirzepatide may interact with insulin and insulin secretagogues, increasing the risk of hypoglycaemia. Always inform your clinician about all medications you are taking.
Concurrent use significantly increases the risk of hypoglycaemia. Doses of insulin or sulfonylurea may need to be reduced when tirzepatide is introduced.
Tirzepatide slows gastric emptying, which may alter the rate (but not generally the extent) of absorption of orally administered drugs. This is particularly relevant for medications where timing of absorption is critical (e.g. oral contraceptives, ciclosporin, levothyroxine). These should be taken at a fixed time relative to tirzepatide injection where possible.
Gastric emptying delay may transiently alter contraceptive pill absorption. Additional contraceptive precautions should be considered, particularly during dose escalation phases.
Terbinafine may alter warfarin metabolism, increasing anticoagulant effect and bleeding risk. INR should be monitored during and after terbinafine courses.
Important Warnings
Cases of acute pancreatitis have been reported with GLP-1 receptor agonists and tirzepatide. Discontinue tirzepatide immediately if pancreatitis is suspected and do not restart. Patients with a history of pancreatitis should not use tirzepatide without specialist assessment.
Tirzepatide is contraindicated in patients with personal or family history of medullary thyroid carcinoma or MEN 2. Report any new neck symptoms to your clinician.
Using tirzepatide alongside insulin or sulfonylureas substantially increases hypoglycaemia risk. Proactive dose reduction of these agents should be considered when initiating tirzepatide. Carry fast-acting glucose at all times if using these combinations.
Gastrointestinal side effects can lead to significant fluid losses. Ensure adequate hydration throughout treatment, particularly during dose escalation. Dehydration can cause acute kidney injury.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Tirzepatide FAQs
Yes. A clinician can assess your eligibility for tirzepatide via a telehealth consultation. They will confirm your BMI, medical history, and suitability, and review whether tirzepatide is appropriate for weight management or type 2 diabetes management.
Clinical trials showed average weight losses of 15–22% of body weight at the highest dose (15 mg) over 72 weeks in people with obesity. Individual results vary depending on dietary adherence, physical activity, baseline weight, and metabolic factors. Tirzepatide is a tool that works best alongside a calorie-reduced diet and regular physical activity.
Some patients notice appetite suppression and early weight loss within the first few weeks. Meaningful, measurable weight loss typically occurs over 3–6 months, with weight loss continuing progressively for up to 12–18 months with consistent treatment.
Weight loss achieved with tirzepatide is not permanent on its own. Clinical evidence from follow-up studies shows that the majority of weight lost is regained within 12 months of stopping treatment, unless sustained lifestyle changes have been maintained. Tirzepatide is considered a long-term treatment for chronic weight management.
No. Both are injectable weekly treatments used for diabetes and weight management, but they are different drugs. Ozempic (semaglutide) is a GLP-1 receptor agonist only. Tirzepatide activates both GIP and GLP-1 receptors simultaneously, which is associated with greater weight loss and glycaemic improvement in head-to-head trials.
Nausea is very common, particularly on starting or increasing doses. This is why the dose escalation schedule begins at 2.5 mg and increases slowly over months. For most patients, nausea improves substantially within 2–4 weeks at each dose level. Eating smaller meals, avoiding high-fat foods, and staying hydrated can help manage gastrointestinal side effects.