In the UK, a routine blood test is not automatically required before starting Mounjaro (tirzepatide). A GPhC-registered prescriber decides on a case-by-case basis after reviewing your online consultation; most people can start based on their medical history, measurements and medication list, but a blood test may be requested if your history suggests it is clinically needed.
Below is what a UK prescriber actually checks before prescribing Mounjaro, when blood tests come into the picture, and how the process works at a regulated pharmacy.
Are blood tests legally required before Mounjaro in the UK?
No single law or MHRA licence condition mandates a blood test for every person before Mounjaro (tirzepatide). The decision sits with the prescriber, who must confirm treatment is clinically appropriate and safe. Many patients are prescribed Mounjaro on the basis of a thorough history and physical measurements alone, while others are asked for bloods first because something in their health picture warrants it.
At The Weight Clinic, every prescription is issued by a GPhC-registered independent prescriber after a free online consultation, and dispensed by our own GPhC-registered pharmacy. Whether a blood test is needed is a clinical judgement, not a fixed step everyone passes through.
What does a prescriber check before prescribing Mounjaro?
A prescriber reviews your full health and weight picture to decide whether Mounjaro is suitable and safe for you. This assessment is the core safety check, and for many people it does not require a blood test.
- Your body mass index (BMI) and weight-related health conditions.
- Your full medical history, including diabetes type, gut conditions, pancreatitis, thyroid history and eating disorders.
- All current medicines, to check for interactions and timing issues.
- Pregnancy status and whether you are planning pregnancy or breastfeeding.
- Any allergies, including to the active ingredient tirzepatide.
Where clinically needed, this is followed by a short video consultation. A prescription is only issued if treatment is clinically appropriate — it is never guaranteed.
Who is and isn't eligible for Mounjaro in the UK?
Mounjaro is licensed for weight management in adults aged 18 or over with a BMI of 30 or more, or a BMI of 27 to 30 alongside a weight-related condition such as type 2 diabetes, high blood pressure or sleep apnoea.
Mounjaro is not suitable if any of the following apply:
- You are pregnant, planning pregnancy, or breastfeeding.
- You have type 1 diabetes.
- You have a personal or family history of medullary thyroid carcinoma or MEN2.
- You have a history of pancreatitis or severe gastrointestinal disease.
- You have an active eating disorder.
- You have severe liver or kidney impairment.
- You have a known allergy to tirzepatide.
Several of these are the reason a prescriber might request a blood test — for example, to assess kidney or liver function, or to clarify diabetes type where it is uncertain.
When would a prescriber ask for a blood test before Mounjaro?
A prescriber may request a blood test before Mounjaro when your history raises a question that measurements and your answers alone cannot resolve. Blood tests are used to confirm safety, not as a hurdle for its own sake.
- Kidney function — relevant because severe kidney impairment makes Mounjaro unsuitable, and significant gut side effects can affect hydration.
- Liver function — to rule out severe liver impairment.
- Diabetes status — an HbA1c or glucose test may clarify whether you have type 2 diabetes (which affects eligibility and monitoring) and helps distinguish it from type 1 diabetes, for which Mounjaro is not suitable.
- Thyroid concerns — where your history flags a relevant risk.
If a blood test is recommended, the prescriber will tell you what is needed and why. Mounjaro and the other options on our treatments page are prescription-only medicines, available only after this clinical assessment.
How does Mounjaro work, and why do the safety checks matter?
Mounjaro (tirzepatide) activates two gut-hormone receptors — GLP-1 and GIP — at the same time, which reduces appetite and helps you feel full sooner. It is a weekly self-injection, started at 2.5mg and titrated upward through 5, 7.5, 10 and 12.5mg to a maximum licensed dose of 15mg.
In the SURMOUNT-1 trial, participants on the 15mg dose lost on average 22.5% of body weight over 72 weeks, alongside lifestyle support (Jastreboff AM, et al. N Engl J Med. 2022;387(3):205–216). Individual results vary; not everyone reaches this.
Common side effects (affecting more than 1 in 10 people) include nausea, diarrhoea, constipation, vomiting, decreased appetite and fatigue. Rare but serious risks include severe allergic reaction, acute pancreatitis, severe hypoglycaemia, severe gastrointestinal disease and worsening diabetic retinopathy. These are why the up-front assessment — and, where indicated, a blood test — matters. You can report any suspected side effect through the MHRA Yellow Card scheme at https://yellowcard.mhra.gov.uk/.
Do the other weight-loss medicines need blood tests?
The same principle applies across the licensed options: a blood test is a prescriber's clinical judgement, not an automatic requirement. The eligibility criteria and safety assessment are consistent whether you are considering an injection or a tablet.
- Wegovy injection (semaglutide) — a once-weekly GLP-1 injection.
- Wegovy Tablet (oral semaglutide) — the same active medicine as a once-daily tablet, taken first thing on an empty stomach with a small sip of plain water, then waiting at least 30 minutes before eating, drinking or taking anything else.
- Foundayo (orforglipron) — a small-molecule GLP-1 tablet, taken once daily at any time of day with or without food or water.
- All weight-loss injections in one place.
Whichever you are suited to, the prescriber decides whether bloods are needed for you specifically.
How does the consultation and prescribing process work?
At The Weight Clinic, the process is designed so that safety checks happen before any medicine is dispensed.
- You complete a free online consultation about your health and weight.
- A GPhC-registered independent prescriber reviews your answers to check that treatment is clinically appropriate and safe.
- A short video consultation takes place where clinically needed, and a blood test may be requested if your history warrants it.
- If suitable, the medicine is dispensed by our UK pharmacy (North Harrow Pharmacy, GPhC registration number 1034996) and sent by tracked delivery, with ongoing prescriber support.
You can confirm our registration on the General Pharmaceutical Council register at pharmacyregulation.org. The online consultation is free; you only pay if a treatment is prescribed and you choose to proceed. You can begin your free eligibility check at any time, and read more about The Weight Clinic or contact us with questions.
This article is for information only and is not a substitute for personalised medical advice. Weight-loss medicines are prescription-only, are not suitable for everyone, and are prescribed only after a clinical consultation with a GPhC-registered prescriber. Individual results vary. Always speak to a UK-registered pharmacist or doctor before starting or changing any prescription medication.
