Zepbound and Mounjaro pens: how many doses, how long they last, and how to manage them
Zepbound and Mounjaro each come in two pens: a single-dose pen that holds one weekly dose, and a KwikPen that holds four. A single-dose pen can spend up to 21 days in total out of the refrigerator, and a KwikPen is finished 30 days after its first use or after its fourth dose, whichever comes first.
Everything below is taken from the FDA labels and Lilly's Instructions for Use, with the revision date of each document beside the claim.
The two kinds of pen
The single-dose pen is the older format. The Instructions for Use for both brands carry the same sentence, with the brand name swapped: "ZEPBOUND is a single-dose prefilled pen" (Zepbound pen Instructions for Use, within the Zepbound label, revised April 2026). One pen, one injection, and the pen goes in a sharps container. A carton holds four.
The KwikPen is the multi-dose format. "Each pen contains 4 fixed doses, one dose taken weekly" (Zepbound KwikPen Instructions for Use, within the Zepbound label, revised January 2026). A carton holds one pen, which covers four weeks.
Both labels list both formats. The Zepbound prescribing information and the Mounjaro prescribing information, both revised August 2026, describe a single-dose pen and a single-patient-use KwikPen side by side.
What each pen holds
| Pen | Doses in the pen | Strength per dose | Volume per dose | Pens per carton |
|---|---|---|---|---|
| Zepbound single-dose pen | 1 | 2.5, 5, 7.5, 10, 12.5 or 15 mg | 0.5 mL | 4 |
| Zepbound KwikPen | 4 | 2.5 mg to 15 mg | 0.6 mL | 1 |
| Mounjaro single-dose pen | 1 | 2.5, 5, 7.5, 10, 12.5 or 15 mg | 0.5 mL | 4 |
| Mounjaro KwikPen | 4 | 2.5, 5, 7.5, 10, 12.5 or 15 mg | 0.6 mL | 1 |
A KwikPen's dose is fixed. The pen for a given strength delivers that strength four times, and the Zepbound label describes it that way: "10 mg/2.4 mL (4.17 mg/mL) for four 2.5 mg/0.6 mL doses" at the low end, "60 mg/2.4 mL (25 mg/mL) for four 15 mg/0.6 mL" at the high end.
Pen needles are a separate item with the Zepbound KwikPen. Its Instructions for Use list a "KwikPen-compatible Pen Needle (not included)" and say to "Always use a new pen needle for each injection".
When a KwikPen is finished
A KwikPen is finished after four doses, even though it will not look empty. The Zepbound KwikPen instructions say: "After 4 doses, throw away (discard) the Pen, including the unused medicine. The Pen will prevent you from dialing a full dose after you have given yourself 4 weekly doses."
The leftover is there by design. Both labels state that "Each single-patient-use KwikPen contains additional volume to allow for device priming."
There is also a clock. The Zepbound KwikPen instructions say to "Throw away the Pen 30 days after first use". The Mounjaro label puts all three limits in one sentence: "Throw away opened multi-dose vial or single-patient-use KwikPen after a total of 30 days at room temperature, 30 days after first use, or after taking 4 weekly doses, even if there is medicine left in it."
How long each pen keeps
All four pens are stored in a refrigerator at 2°C to 8°C (36°F to 46°F), in the original carton, and are never frozen. The labels differ on what happens outside it.
A single-dose pen gets 21 days. Both labels use the same wording: "each single-dose pen or single-dose vial can be stored unrefrigerated at temperatures not to exceed 30°C (86°F) for up to a total of 21 days." The 21 days are a total, so two trips of ten days each use nearly all of it.
A KwikPen gets 30. Unopened and kept cold, it lasts to the expiry date on its label. Per the Mounjaro label, an unopened KwikPen stored at room temperature, up to 30°C (86°F), is thrown away after 30 days, and an opened one can be kept cold or at room temperature until one of the three limits above is reached.
Rotating sites with a pen
Both labels name the same sites and give the same instruction: the abdomen or thigh, or the back of the upper arm when another person injects, and "Rotate injection sites with each dose."
The Zepbound KwikPen instructions add the detail that matters: "Change (rotate) your injection site each week. You may use the same area of your body but be sure to choose a different injection site in that area."
Read plainly, the instruction is about the spot. The same thigh can come up again; the same place on it is what changes. The research on how far apart is far enough is in injection site rotation, which covers insulin as well.
A missed dose, in the label's words
The labels address a missed dose directly, and this page only quotes them. From the Zepbound prescribing information: "If a dose is missed, instruct patients to administer ZEPBOUND as soon as possible within 4 days (96 hours) after the missed dose. If more than 4 days have passed, skip the missed dose and administer the next dose on the regularly scheduled day."
On moving the weekly day, both labels say: "The day of weekly administration can be changed, if necessary, as long as the time between the two doses is at least 3 days (72 hours)." The Mounjaro label gives the same 4 days (96 hours) for a missed dose.
For the injection steps themselves, use Lilly's Instructions for Use for your pen. They are the documents linked above, and this page does not restate them.
Managing a pen in PinTrax
Add the pen and set how many doses it holds: four for a KwikPen, four for a carton of single-dose pens, one for a single pen. Each log takes one off, and the pen reads the way the label counts it: "3 of 4 doses left." There is nothing to mix, so the reconstitution calculator stays out of it. That is for powder vials, and the ready-to-use vial has its own page.
Give the pen an expiry date. For a KwikPen that is 30 days after the first dose, and writing it down on day one beats counting back later.
Log each injection by tapping the exact spot on the body map. PinTrax warns when a tap falls within about 1.4 cm (on a 175 cm body) of any injection from the last 14 days, and suggests the zone that has rested longest. That is the label's "different injection site in that area" turned into something you can see.
A weekly schedule sets the reminder, and the reminder names the compound. When the strength changes, a titration step changes the logged dose from the date you choose.
PinTrax is free for two compounds, with everything stored on your phone and no account. Pricing is here.
Questions
How many doses are in a Zepbound KwikPen?
Four. The Instructions for Use, revised January 2026, say "Each pen contains 4 fixed doses, one dose taken weekly", and the pen will not dial a full dose after the fourth. It is thrown away at that point with the medicine that remains.
What is the difference between the single-dose pen and the KwikPen?
A single-dose pen holds one 0.5 mL dose and is used once; a carton holds four pens. A KwikPen holds four fixed 0.6 mL doses in one pen, and a carton holds one. Both labels list both formats in strengths from 2.5 mg to 15 mg.
How long can a KwikPen be used after the first dose?
Thirty days. The Zepbound KwikPen instructions say to "Throw away the Pen 30 days after first use", and the Mounjaro label gives the same limit alongside four weekly doses, whichever is reached first.
Do I rotate injection sites with a pen?
Yes, per both labels: "Rotate injection sites with each dose." The Zepbound KwikPen instructions add that you may use the same area of the body as long as you choose a different site within it.
Is there a pen tracker for Zepbound or Mounjaro doses and injection sites?
PinTrax counts a pen down in doses, keeps its expiry date, and records each injection as an exact spot on a body map with a proximity warning. It runs on Android, keeps everything on the phone, and needs no account.