What Mounjaro is
Mounjaro is a once-weekly injection for weight management. It copies two gut hormones — GIP and GLP-1 — which together reduce appetite, slow how quickly your stomach empties, and help steady your blood sugar. The EMA marketing authorisation has been valid across the EU since 15 September 2022 under EMEA/H/C/005620, and one central authorisation covers all 27 member states. Alongside the single-dose pre-filled pen, the Spanish register also lists multi-dose KwikPen and vial presentations at every strength — so check which one you actually hold before following any instruction.Mechanism at the receptor level
Tirzepatide is a dual agonist: it activates both GIP receptors and GLP-1 receptors. GIP receptor activation in the hypothalamic arcuate nucleus amplifies the anorectic signal from GLP-1, producing greater weight loss than GLP-1 agonism alone. In the pancreas, both pathways potentiate glucose-dependent insulin secretion from beta-cells and suppress glucagon release from alpha-cells. The GIP component also enhances adipocyte lipid buffering, which may offset the metabolic slowdown seen with caloric restriction.Key trial design — SURMOUNT-1
The primary weight-management trial (NCT04184622) was a double-blind, randomised, placebo-controlled phase 3 study. 2,539 adults with a BMI of 30 kg/m² or greater (or 27 kg/m² plus ≥1 weight-related complication) were assigned 1:1:1:1 to tirzepatide 5 mg, 10 mg, 15 mg or placebo for 72 weeks. All participants received lifestyle counselling. The co-primary endpoints were percent change in body weight and the proportion achieving ≥5% weight loss. The trial employed the treatment-regimen estimand (effects in all participants who received ≥1 dose, regardless of discontinuation). At 72 weeks, mean weight reduction was 15.0% (5 mg), 19.5% (10 mg), 20.9% (15 mg) versus 3.1% with placebo; 85% of participants on the 15 mg dose lost ≥5%. The trial did not measure cardiovascular outcomes as a primary endpoint.Contraindications explained by mechanism
Tirzepatide is contraindicated in personal or family history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia type 2 (MEN 2) because GLP-1 receptor agonism can promote C-cell hyperplasia and MTC in preclinical studies. It is also contraindicated in pregnancy because weight loss offers no benefit during gestation and tirzepatide crosses the placenta in animal models.Population specifics
Experience in severe renal impairment (eGFR <30 mL/min/1.73 m²) and end-stage renal disease is limited; tirzepatide has not been studied in these groups. No dose adjustment is needed for mild-to-moderate renal impairment. In hepatic impairment, exposure is not meaningfully altered in mild-to-moderate disease; no data exist for severe hepatic impairment.Injecting
The injection itself is a fixed sequence. Work through it in this order every week, and check each step against your own leaflet the first few times.1
Wash your hands and check the pen
Check the label, the expiry date and the liquid. If it does not look the way
your leaflet describes, do not use that pen.
2
Attach a new needle
A fresh needle every time, if your presentation uses separate needles.
Needles are single-use.
3
Choose and rotate the injection site
Rotate between abdomen, thigh or upper arm each week. Clean the area
with an alcohol swab and let it dry.
4
Inject just under the skin
Mounjaro is injected subcutaneously. Do not inject into a vein or muscle.
5
Hold it in place for 5 seconds after the click
The injection pen delivers the full dose — keep it still against the skin
for 5 seconds after the click.
6
Remove the needle and dispose of it safely
Put it straight into a sharps container and never reuse it. See
injection sites and sharps disposal.
Pick a day and keep it
Inject on the same day each week. Pick a day that works for you. If you forget a dose, take it within 4 days of the missed dose. If more than 4 days have passed, skip that dose and take your next one on the regular scheduled day. More in missed or late doses.The published dose schedule
Tirzepatide is dosed at 2.5 – 15 mg per week. The published escalation is:This is the published ladder, not an instruction. It is a chronic treatment for
as long as it is beneficial and safe: the doctor reviews your response every
3 months and decides with you whether to continue, adjust or stop.
Storage
Store unused pens in the refrigerator (2–8°C). Once opened, keep at room temperature below 30°C for up to 30 days. Do not freeze. Keep away from direct heat and light.Contact your doctor if
- severe or persistent nausea, vomiting or diarrhoea prevents you from eating or drinking
- you have severe abdominal pain that does not go away
- you notice signs of an allergic reaction — rash, itching, swelling of the face or throat
- any symptom worries you or feels unusual
Start a consultation
Weight-loss consultation
Answer the weight-loss questionnaire and a registered doctor reviews it.
They decide whether treatment is appropriate, which one, and at what dose —
and declining is a normal outcome. See what it costs
and how the review works.