Tirzepatide
Also known as Mounjaro, Zepbound
A weekly injection for weight loss and type 2 diabetes. It's the active ingredient in Mounjaro and Zepbound.
Quick facts
- Status
- Approved medicine in the EU and US
- Evidence
- Approved (large phase 3 trials)
- Taken as
- Injection under the skin once a week (pre-filled pen or vial)
- Common sizes
- Approved as pre-filled pens (and single-dose vials in the US). Multi-mg vials sold online (5–30 mg) are not the approved product.
- Category
- GIP/GLP-1 receptor agonist · weight & blood sugar
How it works
It copies two gut hormones (GLP-1 and GIP) at once. Together they reduce hunger, slow your stomach and improve blood sugar.
What it’s used for
- Weight loss for people with obesity or overweight plus a health problem
- Type 2 diabetes
- Obstructive sleep apnoea linked to obesity (US)
What the research shows
- Large clinical trials with thousands of people.
- At the highest dose, people lost around 20% of their body weight on average.
- Weight usually comes back if treatment stops.
Side effects & risks
- Nausea, diarrhoea, vomiting and constipation, mainly when the dose is increased
- Gallbladder problems and, rarely, pancreatitis
- Can make some birth-control pills work less well
Is it legal?
Approved in the EU (Mounjaro), US (Mounjaro, Zepbound) and UK. Prescription-only — use only under a doctor's supervision.
Storage & safe handling
- Keep unused pens in the fridge (2–8 °C); never freeze them.
- Use a new needle for each injection and rotate sites (stomach, thigh or upper arm).
- Follow your doctor's instructions and the patient leaflet — don't change the dose yourself.
- Get medical help for severe stomach pain, signs of an allergic reaction or persistent vomiting.
Open in PepTimerTrack your protocol, calculate how much to draw and get reminders — free.Open in PepTimer
Sources: EMA product information (EPAR) for Mounjaro; FDA prescribing information for Mounjaro and Zepbound.
Last updated 12 October 2026. Information — not medical advice. PepTimer does not replace a doctor. Many peptides are not approved medicines in the EU, UK or US. Talk to a qualified healthcare provider before starting, changing or stopping any treatment.
Last updated 12 October 2026. Information — not medical advice. PepTimer does not replace a doctor. Many peptides are not approved medicines in the EU, UK or US. Talk to a qualified healthcare provider before starting, changing or stopping any treatment.