When prescribed appropriately, used at the correct dose, and supervised by a clinician, the safety profile is well-characterised. The most common side effects are gastrointestinal (nausea, constipation, diarrhoea) and resolve as the body adjusts. The serious adverse events documented in the US poison centre data are almost entirely related to incorrect dosing, not the drug used correctly.

Can you overdose on Mounjaro by accident?

Yes. The most common scenarios are dialling the wrong dose on a multi-dose pen, repeating a dose because the patient thinks the pen has malfunctioned, drawing the wrong volume from a vial of compounded product, or confusing weekly and daily dosing. All are preventable with proper instruction and supervision at first injection.

What happens if I take Mounjaro daily instead of weekly?

This is one of the documented overdose patterns in the US data. A patient took the medication daily after seeing a family member's prescription, became severely unwell with nausea and vomiting, and required emergency care. Mounjaro is a once-weekly medication. Daily injection is an overdose.

Why is hypoglycaemia a concern even if I am not diabetic?

Up to 9% of overdose cases involve low blood sugar, and the risk is higher in lean and non-diabetic patients, who are also less likely to recognise the symptoms. If you experience sweating, shakiness, confusion or weakness after a dose, eat or drink something with sugar and seek advice.

Is it safe to buy Mounjaro online?

It depends entirely on the service. A registered UK pharmacy operating with proper clinical oversight is different from an offshore site selling compounded product. The pattern in the overdose data is consistent: cases are heavily concentrated in patients who got their medication without in-person assessment, or who got compounded product from outside the regulated supply chain. We are not in the online prescribing business. Our service is in person.

How is your service different from an online weight loss clinic?

Three things. We assess you in person before prescribing. We do baseline blood tests and a body composition scan. We follow you up in person at fixed intervals with the same doctor. The £650 price reflects clinical time and oversight, not dispensing volume.

GLP-1 Overdose Risk 2026 | Mounjaro Safety London | Medical Express Clinic

If you are taking Mounjaro, Ozempic or Wegovy, or considering them, this matters.

Calls to US poison centres about GLP-1 overdoses have risen by nearly 1,500% since 2019, with 3,633 exposure cases reported in just four months of 2025. The figures come from the US National Poison Data Center, but the pattern they describe is not American. It is the predictable consequence of how these drugs are being prescribed and sold, and most of it is happening in the UK too.

To be clear up front: this article is about overdose risk, not about the medication when used correctly. Mounjaro at the prescribed dose, with proper supervision, has a well-characterised safety profile. The cases driving the 1,500% rise are almost entirely about how the medication reached the patient, not the medication itself.

What is actually causing the rise?

Three factors. None of them is the medication itself.

The first is self-administration error. Research cited by the American Gastroenterological Association found that 91% of GLP-1 exposures reported to poison centres came from patient mistakes, and 21% of those happened on the very first use of the injection pen. Patients double-dose after thinking the pen has malfunctioned. They draw the wrong amount from multi-dose vials. They confuse weekly and daily dosing schedules. They inject a full multi-dose pen instead of a single dose.

The second is compounded and unregulated product. In the US, much of the overdose surge has been linked to compounded semaglutide sold through telehealth providers, often in vials rather than pre-filled pens. One published case described a patient who injected 2 mg of semaglutide instead of the prescribed 0.1 mg. Another injected 2.4 mg instead of 0.25 mg. Both at the start of treatment. In the UK, the equivalent risk sits with online pharmacies and the grey market in unregistered products sold direct to consumers.

The third is absent supervision. Patients who buy GLP-1s through online tickbox consultations get a prescription, a pen, and a leaflet. They do not get a clinician watching how they inject, confirming they understand the schedule, or checking blood glucose if symptoms develop. Specialists quoted in the US data identify the highest-risk window as the moment of initiation, the very point at which most online services have already disengaged from the patient.

If you are worried about a dose you have already taken, skip ahead to what to do if you think you have taken too much.

What an overdose actually looks like

Overdose symptoms overlap with normal GLP-1 side effects. The difference is severity and duration.

Symptom category	Typical side effect	Overdose presentation
Gastrointestinal	Mild nausea, occasional vomiting	Severe vomiting, abdominal pain, dehydration requiring IV fluids
Duration	24 to 72 hours, settles with time	Days to over a week
Blood sugar	Normal in non-diabetics	Hypoglycaemia in up to 9% of cases, even in non-diabetic patients
Common outcome	Manageable at home	Emergency department attendance

Hypoglycaemia is the underappreciated risk. It is reported in up to 9% of GLP-1 overdose cases even without insulin or sulfonylurea co-administration, and it is more common in lean and non-diabetic patients. If you are taking a GLP-1 for weight loss rather than diabetes, you are unlikely to be monitoring your blood glucose. That blind spot is part of why these cases reach hospital.

Polysubstance use (combining the medication with other substances) raises the stakes further. Combining GLP-1s with alcohol or cannabis is associated with worse outcomes. Two practices borrowed from bodybuilding circles also increase risk: stacking, which means taking more than one GLP-1 medication at the same time, and cycling, which means deliberately varying the dose for faster weight loss. Both fall outside any prescribing guideline.

What this looks like in the UK

The UK has not published equivalent national poison centre data, but the conditions for the same problem are in place.

Online weight loss services have multiplied. Many operate on a written-questionnaire model with no in-person assessment, no baseline blood tests, and no follow-up beyond automatic prescription renewals. The MHRA has issued warnings about unregulated GLP-1 products sold online. The Advertising Standards Authority has acted against operators promoting prescription-only weight loss medication outside its regulatory framework.

What clinical supervision actually changes

Five things, all of which are absent from a remote prescription model.

Correct patient selection

Not everyone with a high BMI is a sensible candidate for tirzepatide. Patients with personal or family history of medullary thyroid carcinoma, severe gastrointestinal disease, or pancreatitis need to be excluded. So do patients on type 1 diabetes treatment. A private GP consultation taking a proper history catches this. A questionnaire does not.

Baseline blood tests

A blood panel covering full blood count, kidney function, liver function, lipid profile and HbA1c does two things: it screens for contraindications, and it gives a baseline against which side effects can be judged later. Without it, every reported symptom is a guess. We collect baseline laboratories through our onsite blood tests service as part of the package pathway.

Injection technique under supervision

The data is unambiguous on this point. The first injection is the highest-risk dose a patient will ever take. Watching a patient draw up and inject the first dose, with a nurse correcting technique in real time, is the single highest-yield intervention against self-administration error.

Structured follow-up at weeks 4, 8, 12 and 16

Not a renewal click. An actual clinician reviewing weight, side effects, blood pressure, and tolerability. This is when a patient who is struggling gets their dose held or reduced, rather than escalating into the next titration step they are not ready for.

Direct access between appointments

Most overdose cases that reach hospital are patients who did not know who to call when something went wrong. Knowing the name and contact of your prescribing doctor closes that gap.

If you want a service built around these five points, our weight management package is set out below.

Book a doctor-led assessment

How Medical Express Clinic prescribes Mounjaro

Our Harley Street clinic has been operating since 1984 and is CQC-registered. Mounjaro contains tirzepatide, the active ingredient.

Our doctor-led Mounjaro service is in-person and built around the failure points described above: selection, biochemistry, first-dose supervision, structured reviews, and direct access between visits. Our prescribing philosophy is deliberately slower and more thorough than the online-only model because the data on where things go wrong is now consistent enough to ignore.

Step	What happens	Why it matters
Initial consultation (45 mins)	Full history, examination, BMI and BP. Suitability check against NICE NG28 and prescribing guidelines.	Excludes contraindicated patients. Confirms the medication is appropriate, not just available.
Body composition scan	Baseline visceral fat, muscle mass and body fat percentage (delivered alongside our broader health MOT pathway tooling).	Tracks fat loss specifically, not just scale weight.
Blood panel	FBC, U&E, LFT, lipid profile, HbA1c.	Screens for kidney, liver and metabolic contraindications. Establishes a baseline for safety monitoring.
First dose at clinic	Administered in person with technique training from our nurse.	Eliminates the highest-risk first-injection errors.
Reviews at weeks 4, 8, 12, 16	In-person follow-ups with the same prescribing doctor.	Catches side effects early. Adjusts titration. Holds doses where needed.
Direct access between visits	Contact details for your prescribing doctor for queries.	Closes the gap that drives many overdose attendances.

The package is £650. The medication itself is charged separately, starting from approximately £200 per pen, depending on dose and pharmacy. We only prescribe Mounjaro. We do not stock or supply compounded GLP-1 products.

Already taking Mounjaro from another service? When to consider switching.

If you are part-way through treatment with another provider, the following should prompt a second opinion:

●You cannot identify, by name, the doctor who prescribed your medication.
●You started without an in-person assessment or baseline blood tests.
●You have no scheduled follow-up dates with a named clinician.
●You report a side effect and receive a templated reply, not a clinical review.
●You are escalating to higher doses on a fixed schedule with no review of how you tolerated the previous dose.

These are markers of a dispensing service, not a clinical service. We see patients regularly who started elsewhere and want more structured oversight as their dose increases. We will conduct the same initial assessment, blood panel and body composition scan as we would for a new patient in this pathway, then continue your treatment under direct clinical supervision subject to clinician review at your consultation.

Who should not take Mounjaro

We follow the Summary of Product Characteristics and NICE guidance. The medication is not appropriate if you:

have type 1 diabetes
are pregnant, breastfeeding or planning to conceive
are under 18 or over 75
have severe heart failure, severe kidney or liver disease
have a history of severe gastrointestinal conditions including inflammatory bowel disease or gastroparesis (delayed stomach emptying)
have a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2
have a history of pancreatitis

A BMI of 30 or above is the standard threshold. A BMI of 27 with at least one weight-related condition (such as type 2 diabetes, hypertension or obstructive sleep apnoea) may also qualify. Your doctor will confirm.

What to do if you think you have taken too much

First, this is recoverable. The vast majority of cases resolve with supportive care.

If you have injected more than your prescribed dose, or are unsure how much you injected, the safe response is the same regardless of where you got the medication.

Do not take any further doses until you have spoken to a clinician.
Hydrate and rest.
If you develop severe vomiting, abdominal pain that is unrelenting, signs of dehydration, or symptoms of low blood sugar (sweating, shakiness, confusion), attend A&E.
NHS 111 can advise. The National Poisons Information Service (NPIS) is a clinician-only resource, not a public helpline; patients should go via 111 or A&E.
If you are an MEC patient, contact your prescribing doctor directly using the number provided at your initial consultation. We want to hear from you straight away rather than after the fact.

If you are not currently under our care, use NHS 111 or attend A&E as above; do not delay because you cannot reach the original prescribing service.

Book a doctor-led assessment — £650

If you are considering Mounjaro, or already on it through another service and want proper clinical oversight, our weight management package includes the initial consultation, blood panel, body composition scan, first dose and four structured follow-ups with the same doctor.

Book your consultation Call 020 7499 1991

117a Harley Street, London W1G 6AT — CQC registered. UKAS-accredited laboratories. Established 1984.

Knowledge Centre

GLP-1 Overdoses Are Rising. The Pattern Tells You Why.