Tirzepatide dosing for weight loss: what the milligram schedule actually means

What the trial data tells us about the six-strength ladder

The SURMOUNT-1 trial (published in the New England Journal of Medicine and enrolling 2,539 adults with obesity but without type 2 diabetes) tested tirzepatide at 5, 10 and 15 mg maintenance doses over 72 weeks. Participants on 15 mg achieved an average body-weight reduction of around 20–21%. The programme did not test 2.5 mg as a maintenance dose because it was never designed for that role; its function in the licensed schedule is tolerability, giving the body four weeks to adjust before the first real step upward.

Crucially, the results at each maintenance dose differed. People on 10 mg lost meaningfully less on average than those who reached 15 mg, and people on 5 mg less again. This gradient matters: if you want to understand how each step translates into a practical weekly amount, our page on tirzepatide dosing for weight loss explains what the clinical evidence shows at each strength. You can read a fuller breakdown of the dosing steps alongside their clinical context on the tirzepatide dosing overview.

Milligrams versus units: clearing up a common confusion

People sometimes search for tirzepatide doses in units because they are familiar with insulin, which is measured and drawn from a vial in international units. Tirzepatide works differently. Each Mounjaro KwikPen is pre-filled and pre-set to a fixed milligram dose; you do not draw up, measure or calculate anything. One press of the pen delivers the complete dose. The figure on the box (2.5 mg, 5 mg, 7.5 mg and so on) is the full weekly dose, expressed in milligrams, not in units.

The practical upshot: if you see a dose described in "units" in a forum or on a product listing, treat that as a red flag. Our guide to tirzepatide dosing in units explains why that framing does not apply to licensed Mounjaro pens, which use milligrams only, and any product claiming otherwise is not describing the licensed medicine. For anyone still uncertain about how milligrams and units relate to one another, our dedicated page on tirzepatide units covers the distinction in plain terms. A quick check of the box label before each injection takes under ten seconds and confirms you have the right strength.

The four-week titration rhythm and why it matters for side effects

The graduated schedule is not arbitrary. GLP-1 and dual-agonist medicines slow gastric emptying, and moving too quickly through dose increases is the most common driver of pronounced nausea and vomiting. The NHS patient information for tirzepatide reflects this, describing the typical four-weekly escalation and noting that gastrointestinal effects are most common after starting or after a dose increase, usually settling within days to around two weeks.

Because the side-effect curve is dose-related, your prescriber may recommend staying longer at a given strength if your tolerance has been difficult, this is a clinically reasonable decision, not a sign that treatment has failed. Equally, if 15 mg is not tolerated, a lower maintenance dose can still produce significant results; the SURMOUNT-1 data at 10 mg and 5 mg support this. For a visual reference of how the strengths sequence, the tirzepatide dosing chart lays out the schedule clearly. Detailed clinical dosing considerations are also covered in the BNF's tirzepatide entry, which is the reference UK prescribers use.

Who the licensed schedule is designed for, and the prescriber's role

Under its UK licence, tirzepatide is approved for adults with a BMI of 30 or above, or a BMI of 27 or above alongside at least one weight-related condition such as high blood pressure, high cholesterol, obstructive sleep apnoea, prediabetes or type 2 diabetes. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. BMI alone does not decide suitability; a prescriber reviews the full clinical picture before approving any prescription and before any dose increase.

Tirzepatide is not licensed for anyone under 18, and it is not recommended during pregnancy, while breastfeeding, or for those actively trying to conceive. Women taking oral contraceptives should discuss additional precautions with their prescriber for the first four weeks of treatment and for four weeks after each dose increase, since tirzepatide's effect on gastric emptying may reduce oral contraceptive absorption.

If you are considering private treatment and want to understand whether the schedule is right for you, the weight-loss treatments page explains how a consultation works. For broader context on how tirzepatide fits within the UK landscape of weight-loss options, including NHS eligibility, that page is a useful starting point. Our clinical team reviews every consultation personally, a prescriber, not software, reads your answers the same day and determines which strength, if any, is appropriate.