Anyone reading about Mounjaro (tirzepatide) for the first time tends to notice the same thing: the medicine does not have a single dose. It has a ladder of them, running from 2.5mg a week up to a maximum of 15mg a week, with a minimum of four weeks on each rung before a prescriber considers moving up. That stepped approach has a name — titration — and it is one of the more clinically important features of how the medicine is used.
Tirzepatide is a dual GIP and GLP-1 receptor agonist, given as a once-weekly subcutaneous injection, and manufactured by Eli Lilly under the brand name Mounjaro. In the UK it is a prescription-only medicine. It cannot be supplied without a consultation with a prescriber, and the dose schedule an individual follows is set by that prescriber rather than chosen by the patient.
What follows is background reading rather than a set of instructions: what the titration schedule is for, why the first dose is deliberately not a therapeutic one, and what a prescriber weighs up at a review. Nobody should adjust their own dose or move faster than their prescriber has set out.
What titration means and why it exists here
Titration is the practice of introducing a medicine at a low dose and increasing it in defined increments until an effective, tolerated dose is reached. It is used wherever the body needs time to adapt to a drug’s effects, and it is standard practice with the GLP-1 and dual-agonist class.
Tirzepatide slows gastric emptying and acts on appetite regulation. Those are the mechanisms behind its effect on weight, and they are also the mechanisms behind most of its common side effects. Introducing the full strength immediately would expose the digestive system to the whole of that change at once. Starting low gives the gut several weeks to accommodate before anything is added.
The schedule is therefore not a countdown to be rushed. It is a structured way of finding, for one person, the smallest dose that produces a useful response without unacceptable side effects. Two people who start on the same day may be on quite different doses six months later, and both may be exactly where they should be.
Why 2.5mg is a starting dose, not a treatment dose
The first four weeks at 2.5mg weekly are best understood as a tolerance-building phase. In the UK licensing and prescribing information, 2.5mg is described as a starting dose and is not intended as a maintenance dose for weight management. It exists to let the body meet the medicine gently.
This matters because people sometimes judge the medicine on those first four weeks. Appetite changes at 2.5mg are usually modest, and some people notice very little. That is not a sign the medicine is not working; it is a sign the schedule is doing what it was designed to do. The clinical response is expected to build as the dose steps up.
The four-week minimum between increases
After the initial four weeks, increases are made in 2.5mg steps and no sooner than every four weeks: 5mg, then 7.5mg, 10mg, 12.5mg and, at most, 15mg weekly. Four weeks is a minimum interval, not a fixed timetable. A prescriber can hold someone at a dose for longer than four weeks, and frequently does.
Four weeks reflects both how long the medicine takes to reach steady levels in the body on a weekly injection and how long gastrointestinal side effects typically take to settle. Increasing before that window has passed risks stacking a new adjustment on top of one the body has not finished making.
The strengths, the packs and what they cost
Mounjaro is supplied as a KwikPen, a pre-filled multi-dose pen, dispensed in four-week packs — one pen covering four weekly doses at a single strength. Each pen is a fixed strength, so moving up a step means a different pen rather than a different setting, which is why the four-week block is the natural unit of supply.
The table below sets out the strengths alongside the prices listed by one UK registered online pharmacy. These are prices at the time of writing, shown to illustrate how cost changes across the schedule; they can change and they differ between providers.
Strength (weekly)Role in the scheduleListed price per 4-week pack (at the time of writing)2.5mgStarting dose — tolerance building, not a treatment dose£1455mgFirst maintenance-level dose£1797.5mgIntermediate step£22010mgIntermediate step£24512.5mgIntermediate step£27015mgMaximum licensed weekly dose£287
Cost does not rise in proportion to strength, which occasionally leads people to assume that going higher is better value. That reasoning does not hold clinically: the right dose is the one a prescriber judges appropriate for the individual.
Anyone comparing UK providers should check that the pharmacy is registered with the General Pharmaceutical Council and that the process involves a genuine clinical assessment. Where people search online to buy mounjaro, what they should find is a UK registered pharmacy requiring an online consultation reviewed by a prescriber before anything is dispensed — never a site willing to send pens without one.
That distinction is a safety matter rather than a formality. The MHRA has repeatedly warned about counterfeit weight-loss pens sold through social media and unregistered websites, where the contents, strength and sterility are all unknown. A registered pharmacy such as Cured Pharmacy operates under GPhC oversight with a named superintendent pharmacist, and its prescribers assess eligibility before supply — which is the entire point of the prescription-only classification.
Why a prescriber may hold, slow down or step back
Moving up the ladder is a clinical decision, not an automatic one. There are several common reasons a prescriber does something other than increase at the four-week mark.
- It is working at the current dose. If someone is responding well and tolerating the medicine, there may be no clinical reason to add more. Holding at a lower dose is a legitimate and common outcome.
- Side effects have not settled. If nausea, vomiting or diarrhoea are still troublesome, adding 2.5mg is likely to compound the problem rather than resolve it.
- The person is unwell or dehydrated. Persistent vomiting or diarrhoea carries a risk of dehydration and, in turn, kidney injury, so a prescriber may pause rather than progress.
- A step back is needed. Returning to a previously tolerated dose is a recognised option and is not a failure of treatment.
- Circumstances have changed. New medicines, a planned pregnancy, surgery or a new diagnosis can all change the picture.
The maximum licensed weekly dose is 15mg, but reaching it is not a goal in itself. Many people do well below the maximum and never need the top of the range.
How side effects cluster around the steps
The most common side effects are gastrointestinal: nausea, diarrhoea, vomiting, constipation, reduced appetite and abdominal discomfort. Their timing follows a fairly recognisable pattern — they tend to be at their most noticeable in the first weeks of treatment and again in the days after each dose increase, then ease as the body adapts.
Less common effects include injection-site reactions, fatigue, dizziness and hair thinning. The risk of low blood sugar is higher for people also taking insulin or a sulfonylurea. Uncommon but serious problems include pancreatitis, gallbladder problems, and dehydration or kidney injury following persistent vomiting — all reasons to seek medical attention rather than wait.
Tirzepatide is not suitable during pregnancy or breastfeeding, or for people with a personal or family history of medullary thyroid carcinoma or MEN2. Caution applies with a history of pancreatitis, severe gastrointestinal disease or diabetic retinopathy. There is also specific MHRA advice for people using oral contraceptives: an additional barrier method, or a switch to a non-oral contraceptive, is advised for four weeks after starting tirzepatide and for four weeks after each dose increase, because delayed gastric emptying can reduce absorption.
It is also worth being clear about the context. Tirzepatide is prescribed for adults meeting defined eligibility criteria — generally a BMI of 30 or above, or 27 or above alongside a weight-related condition such as type 2 diabetes, hypertension or dyslipidaemia, where lifestyle change alone has not been enough. It is used alongside diet, physical activity and ongoing clinical support, not instead of them.
Pens, storage and the leaflet in the box
Pens should be kept refrigerated at 2–8°C. A pen may be kept out of the fridge for a limited period at up to 30°C, and the exact allowance is set out in the patient information leaflet supplied with the medicine. That leaflet is the authoritative document for storage, handling, injection technique and what to do about a missed dose, and it should be read in full rather than skimmed.
Practically, the four-week pack and the fridge requirement mean some planning around deliveries, holidays and travel. Anyone unsure about storage in a specific situation should ask their pharmacist rather than guess.
What happens at a review
Reviews are how the schedule stays individual. A prescriber will typically look at:
- Weight and other measurements, and the trend rather than a single reading.
- Side effects — what has occurred, how severe, and whether it has settled.
- Eating, hydration and activity, including whether nutrition has been adequate.
- Other medicines and conditions, and any changes since the last check.
- Whether to increase, hold, reduce or stop — and the reasoning behind it.
A review is also the right place to raise anything that has felt off. Between reviews a GP or pharmacist can advise, and anything suggesting a serious reaction warrants urgent medical attention.
Frequently asked questions
Does everyone reach 15mg?
No. 15mg is the maximum licensed weekly dose, not a target. Prescribers frequently hold people at a lower dose that is working and well tolerated, and many never go to the top of the range.
Why must there be four weeks between increases?
Four weeks is the minimum interval in the standard schedule. It allows levels of a once-weekly medicine to stabilise and gives common gastrointestinal side effects time to settle before another change is introduced. A prescriber can extend the interval but should not shorten it.
Can someone move up faster if they want quicker results?
No. The schedule is set by a prescriber for the individual, and self-adjusting the dose is unsafe. Increasing early tends to worsen side effects without a corresponding benefit; anyone who thinks their schedule needs changing should raise it at a review.
Is Mounjaro available without a prescription in the UK?
No. It is a prescription-only medicine, supplied only after a consultation with a prescriber, whether through the NHS or a registered pharmacy. Any seller offering it without one — including social media accounts and unregistered websites — should be avoided entirely.
The short version
The dose ladder is not bureaucracy. Starting at 2.5mg, waiting at least four weeks between steps, and stopping wherever the balance of benefit and tolerability lands are all deliberate features built around how the medicine behaves in the body, and the endpoint that matters is the dose that suits one person — which may be well below 15mg. The schedule belongs to the prescriber who set it, informed by the individual in front of them, and it can be held, slowed or reversed as circumstances change.
This article is general information and is not medical advice. It is not a recommendation to start, change or stop any treatment. Speak to your GP, pharmacist or prescriber about your own circumstances, and read the patient information leaflet supplied with any medicine before use.
