# How a weekly jab builds up

> Over about a month. Mounjaro’s product information says its level settles after 4 weeks of weekly doses, and Ozempic’s says 4 to 5. Both peak within a few days of each jab, then fade slowly, so the next lands before the last has gone and the level climbs in steps. Ozempic’s stays about 5 weeks after a last dose.

Canonical: https://jabwise.app/guides/how-a-weekly-jab-builds-up. Sources checked 12 October 2026. General information, not medical advice: follow your prescriber.

## See it build

Drawn from the published models Jabwise uses, for the same dose on time every week. It shows the shape of a build-up, not your own level: bodies and doses differ.


## In their own words

From each medicine’s product information, written for prescribers.

- **Mounjaro**: Peak after a dose: "reached 8 to 72 hours post dose" ([Mounjaro product information (SmPC)](https://www.medicines.org.uk/emc/product/15481/smpc)); Half-life: "elimination half-life of approximately 5 days" ([Mounjaro product information (SmPC)](https://www.medicines.org.uk/emc/product/15481/smpc)); Settled after: "4 weeks of once weekly administration" ([Mounjaro product information (SmPC)](https://www.medicines.org.uk/emc/product/15481/smpc))
- **Ozempic**: Peak after a dose: "reached 1 to 3 days post dose" ([Ozempic product information (SmPC)](https://www.medicines.org.uk/emc/product/9750/smpc)); Half-life: "elimination half-life of approximately 1 week" ([Ozempic product information (SmPC)](https://www.medicines.org.uk/emc/product/9750/smpc)); Settled after: "4–5 weeks of once weekly administration" ([Ozempic product information (SmPC)](https://www.medicines.org.uk/emc/product/9750/smpc))
- **Wegovy**: Peak after a dose: Not stated; Half-life: "prolonged half-life of around 1 week" ([Wegovy product information (SmPC)](https://www.medicines.org.uk/emc/product/102093/smpc)); Settled after: Not stated

## What the numbers say

- **A few days to peak**: 8 to 72 hours after a Mounjaro dose, and 1 to 3 days after an Ozempic dose, their product information says.
- **A month to settle**: Mounjaro settles after 4 weeks of weekly doses, and Ozempic after 4 to 5, their product information says.
- **Weeks to leave**: Their product information says about 5 weeks after a last Ozempic dose, 7 after a last 2.4mg Wegovy dose.

## Questions

### Why does a weekly jab build up?

Each dose fades slowly. Tirzepatide’s half-life is approximately 5 days and semaglutide’s about 1 week, so some of last week’s dose is still there when the next one goes in.

### How long does it stay after a last dose?

Ozempic’s product information says semaglutide will be present for about 5 weeks after the last dose, and Wegovy’s says approximately 7 weeks after the last 2.4mg dose. If you’re thinking of stopping, the NHS says talk to your doctor and don’t stop suddenly.

### Is the chart my actual level?

No. It’s an estimate from published models of how these medicines behave on average. Jabwise draws the same estimate from your own logged doses, and labels it as one.

## In Jabwise: Medication level

See your own week in Jabwise. Jabwise draws the same estimate from your dose history, as a share of your usual peak, and says whether it’s building up, rising or easing. It’s an estimate, never a measurement.

## Getting real advice

- **A pharmacist, your doctor or NHS 111**: If you’re not sure how to use your medicine, or a side effect bothers you or won’t go away. NHS 111 if you think you might be having serious side effects, or you’ve used too much. [NHS: Semaglutide](https://www.nhs.uk/medicines/semaglutide/), [NHS: Tirzepatide](https://www.nhs.uk/medicines/tirzepatide/), [NHS 111 online](https://111.nhs.uk/)
- **Report a side effect**: Anyone can, not only doctors. [Yellow Card (UK)](https://yellowcard.mhra.gov.uk/), [MedWatch (US)](https://www.fda.gov/safety/medwatch-fda-safety-information-and-adverse-event-reporting-program)

## Sources

- [Mounjaro product information (SmPC)](https://www.medicines.org.uk/emc/product/15481/smpc)
- [Ozempic product information (SmPC)](https://www.medicines.org.uk/emc/product/9750/smpc)
- [Wegovy product information (SmPC)](https://www.medicines.org.uk/emc/product/102093/smpc)
- [NHS: Semaglutide](https://www.nhs.uk/medicines/semaglutide/)
- [NHS: Tirzepatide](https://www.nhs.uk/medicines/tirzepatide/)