Zepbound Half-Life
See the dosage chart to find out how long Zepbound stays in your system.
Chart your Zepbound injection half-life
How Zepbound dosing works
Zepbound starts at 2.5 mg once a week for 4 weeks, then goes up to 5 mg. After that, the dose can increase by 2.5 mg no sooner than every 4 weeks. The maintenance doses are 5 mg, 10 mg or 15 mg, and 15 mg is the maximum.
Zepbound is sold in the United States and, as a KwikPen, in Canada. Elsewhere, the same medicine and dose steps are sold as Mounjaro. Mounjaro dosage chart and half-life →
- Starting doseMonth 1Weeks 1–42.5 mgonce a week
- Maintenance optionMonth 2Weeks 5–85 mgonce a week
- Step upMonth 3Weeks 9–127.5 mgonce a week
- Maintenance optionMonth 4Weeks 13–1610 mgonce a week
- Step upMonth 5Weeks 17–2012.5 mgonce a week
- Maximum doseMonth 6 onwardWeek 21 onward15 mgonce a week
Zepbound dosing schedule by week
| When | Weekly dose | What this step is for |
|---|---|---|
| Weeks 1–4Month 1 | 2.5 mg | Starting doseHelps your body get used to tirzepatide. It is not approved as a maintenance dose. |
| Weeks 5–8Month 2 | 5 mg | Maintenance optionFirst increase, from week 5 at the earliest. The lowest maintenance dose. |
| Weeks 9–12Month 3 | 7.5 mg | Step upNext step from week 9 at the earliest, if your prescriber increases the dose. |
| Weeks 13–16Month 4 | 10 mg | Maintenance optionFrom week 13 at the earliest. A maintenance dose, also for sleep apnoea. |
| Weeks 17–20Month 5 | 12.5 mg | Step upFrom week 17 at the earliest, on the way to 15 mg. |
| Week 21 onwardMonth 6 onward | 15 mg | Maximum doseFrom week 21 at the earliest. The highest maintenance dose. |
Get reminders for every Zepbound jab and track each dose step in Glapp
Rated Excellent on Trustpilot. (opens in a new tab)
How long does Zepbound stay in your system?
Zepbound (tirzepatide) has a half-life of about 5 days, so the amount in your body falls by about half every 5 days after your last jab. About 2 weeks after the last dose roughly 17% of the peak level is left, and after about 4 weeks it is under 3%, so most of it is gone about a month after your last jab.
- Half-life
- About 5 days (the Zepbound label says 5 to 6 days)
- Highest level
- 8 to 72 hours after a jab, typically about 24 hours
- Steady state
- After about 4 weeks on the same dose
- Mostly cleared (under 3%)
- About 4 weeks after the last dose
The Zepbound prescribing information does not say how long tirzepatide stays in the body. A common rule of thumb is 5 half-lives, which for tirzepatide is about 25 to 30 days.
Zepbound is sold in the United States and, as a KwikPen, in Canada. In the EU, the UK, Brazil and many other countries, the same medicine is sold as Mounjaro.
Zepbound half-life chart
Estimated share of the medicine left after your last jab, compared with the highest level just after that jab. It assumes you had been on the same dose for at least 4 weeks.
| Time since your last jab | Estimated level left |
|---|---|
| 1 week (7 days) | 44% |
| 2 weeks (14 days) | 17% |
| 3 weeks (21 days) | 6.4% |
| 4 weeks (28 days) | 2.4% |
| 5 weeks (35 days) | 0.9% |
| 6 weeks (42 days) | 0.3% |
When to increase your Zepbound dose
Each increase comes after at least 4 weeks on the current dose, and only if you tolerate it and your prescriber decides you need a higher dose. Many people stay longer on a dose than the chart shows.
The slow steps help limit nausea, diarrhoea and other stomach side effects. If side effects are hard to manage, your prescriber may keep you on a dose longer before the next step.
What is the maximum dose of Zepbound?
The maximum dose of Zepbound is 15 mg once a week. Following the label schedule, the earliest you can reach it is week 21.
For obstructive sleep apnoea, the label recommends a maintenance dose of 10 mg or 15 mg. For weight management, 5 mg, 10 mg and 15 mg are all maintenance doses.
Zepbound pens and strengths
Single-dose pens come in all six strengths, from 2.5 mg to 15 mg, and each pen delivers one full dose.
In the US, single-dose vials in every strength and the KwikPen, which holds 4 weekly doses, are sold through LillyDirect. In Canada, Zepbound is sold as a KwikPen.
If you miss a dose of Zepbound
If you miss a dose, take it within 4 days (96 hours) of the missed day. If more than 4 days have passed, skip it and take the next dose on your usual day.
You can change your injection day as long as the two doses are at least 3 days (72 hours) apart.
After one dose vs. after months on Zepbound
The level falls by about half every 5 days, whether you took a single jab or have been on Zepbound for months. What changes is the starting point: after several weeks on the same dose the jabs overlap, and the peak is about 1.6 times higher than after one jab, so there is more to clear. As a share of the peak, the timeline in the table above applies either way.
Why Zepbound can feel weaker before your next jab
Zepbound peaks about 20 hours after a jab, once you are on a steady dose. By the day of your next weekly jab, the estimated level is about 44% of that peak, so some people notice more hunger or fewer side effects late in the week. This is expected with once-weekly dosing. If it bothers you, talk to your prescriber rather than changing your schedule on your own.
Can you flush Zepbound out of your system faster?
No. There is no proven way to speed up how your body clears tirzepatide. Drinking more water, exercising or fasting does not shorten its half-life, because it is broken down slowly by normal metabolism rather than flushed out. If side effects are the problem, contact your healthcare professional.
Stopping Zepbound before surgery or pregnancy
Pregnancy: the US label says to stop Zepbound when a pregnancy is recognised. In the EU and the UK, where tirzepatide is sold as Mounjaro, the label advises stopping at least 1 month before a planned pregnancy because of the long half-life.
Birth control pills: Zepbound can make them less reliable. The label advises switching to a non-oral method, or adding a barrier method, for 4 weeks after starting Zepbound and for 4 weeks after each dose increase.
Surgery: Zepbound slows stomach emptying, which matters for anaesthesia and deep sedation. The label asks you to tell your healthcare team about any planned surgery or procedure; they decide whether and when to pause it.
Frequently asked questions about Zepbound
What is the starting dose of Zepbound?
2.5 mg once a week for the first 4 weeks. It is a starting dose only; the label does not approve 2.5 mg for maintenance.
How often can you increase the Zepbound dose?
No sooner than every 4 weeks, in 2.5 mg steps, and only if you tolerate the current dose. Your prescriber decides whether and when to increase.
Do you have to go up to 15 mg?
No. The maintenance doses are 5 mg, 10 mg and 15 mg. You can stay on 5 mg or 10 mg if that dose works for you, as agreed with your prescriber.
How long does it take to reach the maximum Zepbound dose?
At least 20 weeks: 4 weeks each on 2.5 mg, 5 mg, 7.5 mg, 10 mg and 12.5 mg, so 15 mg starts in week 21 at the earliest.
What if I miss several Zepbound doses?
For one missed dose, take it within 4 days or skip it. The label does not give a rule for several missed doses, so ask your prescriber before restarting; you may need a lower dose again.
Is the Zepbound dosage the same as Mounjaro?
Yes. Both use the same tirzepatide dose steps from 2.5 mg to 15 mg. Only the brand name and the approved uses differ.
What is the half-life of Zepbound?
About 5 days. The Zepbound prescribing information gives 5 to 6 days for adults with overweight or obesity. This long half-life is what allows one jab a week.
How long does Zepbound stay in your system after one jab?
After a single jab the level also halves about every 5 days and drops under 3% of its peak after about 4 weeks. The difference from stopping after months is the starting point: one jab gives a lower peak, so there is less to clear.
When does Zepbound peak after an injection?
Tirzepatide reaches its highest level 8 to 72 hours after a jab, typically about 24 hours, according to the prescribing information.
Why does Zepbound seem to wear off before the next dose?
With weekly jabs, the estimated level just before the next dose is about 44% of the peak, so some people notice more hunger late in the week. If this bothers you, discuss it with your prescriber instead of changing your dose or schedule yourself.
Does a higher Zepbound dose stay in your system longer?
Not as a share of the peak. The half-life is the same from 2.5 mg to 15 mg, so the level halves about every 5 days at any dose. A higher dose starts from a higher level, so it takes a few more days before only a trace is left.
Are Zepbound and Mounjaro the same medicine?
Yes. Both contain tirzepatide made by Eli Lilly and have the same half-life. In the US, Zepbound is approved for weight management and obstructive sleep apnoea, while Mounjaro is approved for type 2 diabetes.
Does it matter if I use a pen, a vial or the KwikPen?
No. Single-dose pens, vials and the KwikPen deliver the same tirzepatide, so the estimate depends only on your dose and the dates of your jabs.
How the estimate works
The calculator uses a one-compartment model with first-order absorption, the standard way to describe a weekly injection. It uses average values for tirzepatide: a half-life of 5 days, a peak 1 day after a single jab and 80% absorption from the injection site. Real levels vary from person to person, and the model does not show how well the medicine works for you.
Data Sources
Label facts on this page come from these sources:
- Zepbound US prescribing information — Eli Lilly, FDA-approved label
- Mounjaro EU product information — EMA summary of product characteristics
- Tirzepatide clinical pharmacology review — FDA, NDA 215866
Check Our Other Free Tools
- Mounjaro dosage chart and half-life
- Zepbound pen clicks
- Zepbound vial units
- Split dose calculator
- GLP-1 dose plotter
- Titration planner
- Missed dose guide
Important
This page is general information, not medical advice. Levels shown are estimates from a model, not lab results. Follow your prescriber and the instructions that come with your medicine.