Semaglutide to tirzepatide restarts the escalation and changes three practical numbers: the storage clock, the missed-dose window, the device.
Key points
- 01Two different molecules with two different labels. Wegovy is semaglutide, which acts at the GLP-1 receptor. Zepbound is tirzepatide, which acts at both the GIP and the GLP-1 receptor. They are separate medicines, so nothing carries over automatically, and several of the practical numbers you have memorised over the past year are about to change.
- 02The escalation restarts at the bottom. The Zepbound label opens at 2.5 mg once weekly for four weeks for everyone, whatever they were taking before. Having reached the 2.4 mg maintenance dose of Wegovy does not buy a higher starting rung. Any attempt to map one onto the other belongs with your prescriber, and this page will not attempt it.
- 03The step pattern is different in shape, not just in numbers. Wegovy climbs through four fixed four-week steps to a named maintenance dose. Zepbound starts at 2.5 mg, moves to 5 mg after four weeks, then rises in 2.5 mg increments after at least four weeks each, with 5, 10 and 15 mg as the maintenance doses. The second schedule has more optional rungs.
- 04The missed-dose window changes from two days to four. This is the change that most often catches people out. Wegovy turns on whether the next scheduled dose is more than two days away. Zepbound allows a missed dose to be taken within four days, which is 96 hours, and skipped after that. Two different rules, and the old one no longer applies.
- 05The storage clock changes from 28 days to 21. Both live at 2 to 8 C in the refrigerator. Wegovy is allowed a longer stretch out of the fridge than Zepbound, which the label permits for up to 21 days at no more than 30 C. If your travel and holiday planning was built around the longer number, rebuild it around 21 days.
- 06You may now have a choice of presentation. Zepbound is supplied both as a single-dose pen and as single-dose vials that need a separate sterile syringe. Wegovy users are usually used to a self-contained pen, so the vial route is a genuinely new procedure. Our guide to injecting Zepbound from a vial covers the draw-up if that is what you were dispensed.
- 07The injection sites and rotation do not change. Abdomen, thigh and the back of the upper arm remain the subcutaneous sites, and the reasons to rotate are identical. Keep the pattern you already have rather than resetting it. This is the part of the routine that transfers intact, and it is worth saying because most other parts do not.
- 08Tolerance does not transfer between the two. Whatever your gut adapted to on semaglutide, tirzepatide starts that process again, which is what the four weeks at 2.5 mg are for. Early nausea after a switch is a recognised pattern rather than a sign the switch has failed. Log how many days it lasts, since that is the datum the next appointment turns on.
- 09The gap between the last Wegovy dose and the first Zepbound dose is clinical. How long to leave between the two, and which day of the week to restart on, are decisions for your prescriber. Ask for both in writing at the switch appointment, and write them into your record before you leave, because that interval is not something to reconstruct from memory later.
- 10Do not keep leftover Wegovy pens as a backup. They are a medication you are no longer prescribed, and a saved pen is how a supply gap turns into self-treatment. Handle each one as sharps disposal plus medication disposal, which are two separate problems. Our posts on disposing of needles and of unused medication cover both halves.
- 11Re-read the storage panel, not just the dose. The instructions for use in the new carton carries three numbers: the refrigerated range, the days allowed at room temperature and the conditions that mean discard. People reliably carry over the first from the old product and improvise the others. Write all three on the new carton on day one.
- 12Restart the record rather than continuing the old one. New medication, new strength, new device type, new lot number, new expiry, and a new escalation clock counting four-week blocks. A switch is the most likely moment in a year for a doubled or missed dose, precisely because the weekly rhythm you trusted has just been rebuilt.
- 13Seven questions for the switch appointment. Which day do I start, how long after the last Wegovy dose, pen or vial, which strengths am I getting and for how long, what is the missed-dose rule now, how many days may it sit out of the fridge, and what should I do with the pens I still have.
- 14Three numbers to rewrite on day one. The missed-dose window, the days allowed out of the fridge, and the minimum gap between two doses if you move your injection day. All three differ between the two products, and all three are the numbers people recall wrongly under pressure. Write them on the new carton in pen.
- 15The device may not be a pen at all. Coming from a self-contained single-dose pen, a single-dose vial is a genuinely different procedure with a separate syringe, a draw-up step and sterile handling at the stopper. Find out which one your prescription is for before the first dose, not on the evening of it.
- 16Your sharps container may need resizing. A whole pen and a syringe fill a container at different rates, and a vial route also produces empty glass. Check what a month of the new format actually generates against the container you have, and know where the full one goes before it is full.
- 17Give the pharmacy notice, not a same-day request. A switch is a new product and often a new authorisation. Ask about lead time before your last dose of the old medicine, so that any gap between the two is an interval your prescriber chose rather than one the paperwork imposed.
- 18Comparing week two against your old maintenance dose is unfair. You are moving from a fully titrated dose to a starting dose, so the first month is not a like-for-like test of the new medicine. Most disappointment after a switch comes from making that comparison anyway. Judge it at a comparable point in the schedule.
- 19Bring the old problems to the switch appointment. A recurring lump at one site, a reaction that only ever appeared in the thigh, a pen that failed part-way through a dose. Much of that is device-related rather than drug-related, and the switch appointment is the natural moment to raise it while the whole picture is being reviewed.
Common mistakes
Carrying the two-day missed-dose rule across
FixThe new rule is a four-day window, meaning 96 hours, after which the dose is skipped. Write the new rule on the carton, because the old one will be the first thing that comes to mind under pressure.
Planning travel on the old storage number
FixTirzepatide is allowed up to 21 days at no more than 30 C, which is shorter than what you were working with. Recount any trip that was planned around the longer allowance.
Assuming you will get a pen
FixBoth a single-dose pen and single-dose vials exist, and the vial route needs a separate sterile syringe for every dose. Ask the pharmacy which one your prescription is written for before you need it.
Expecting to start above 2.5 mg
FixThe label opens everyone at 2.5 mg once weekly for four weeks whatever they took before. Reaching a maintenance dose on semaglutide does not shorten the tirzepatide ramp.
Continuing the old injection record
FixStart a fresh one. New medication, new strength, new device, new lot number and a new four-week escalation clock, all of which the old sheet will quietly misrepresent.
Keeping leftover Wegovy pens for a supply gap
FixThey are a medication you are no longer prescribed. Handle the sharps and the medicine as two separate disposal problems, both covered in our disposal guides.
When to call a clinician
- Severe upper abdominal pain that may radiate to the back, with or without vomiting, which can indicate pancreatitis.
- A lump or swelling in the neck, hoarseness or trouble swallowing. Both medicines carry a boxed warning for thyroid C-cell tumours.
- Swelling of the face, lips, tongue or throat, or difficulty breathing, which can indicate a serious allergic reaction. Seek emergency care.
- Vomiting or diarrhoea severe enough that fluids will not stay down during the reintroduction weeks.
- Severe pain in the upper right abdomen with fever, nausea or yellowing of the skin, which can indicate gallbladder disease.
Frequently asked questions
Is there a dose conversion from Wegovy to Zepbound?+
No published equivalence exists. The Zepbound label starts everyone at 2.5 mg once weekly for four weeks regardless of prior treatment, and your prescriber sets the plan. Educational information only, not medical advice.
Does the missed-dose rule change?+
Yes, and this is the change people miss. Zepbound allows a missed dose to be taken within four days, which is 96 hours, and skipped after that. Wegovy turns on whether the next scheduled dose is more than two days away.
How long can Zepbound stay out of the fridge compared with Wegovy?+
Zepbound is allowed up to 21 days at no more than 30 C. That is shorter than the room-temperature allowance you were working with on Wegovy, so travel plans need rebuilding around the smaller number.
Will I get a pen or a vial?+
Both presentations exist. The pen is self-contained, while a single-dose vial needs a separate sterile syringe for each dose. Ask the pharmacy which one your prescription was written for, because the procedures are not the same.
Will the side effects come back?+
Tolerance built on semaglutide does not transfer to tirzepatide, so the reintroduction at 2.5 mg often brings early gastrointestinal effects back for a while. Record how long they last for your next appointment.
Can I keep my remaining Wegovy pens?+
No. They are a medication you are no longer prescribed. Dispose of the sharps in a hard container and handle the medication itself through a take-back route or your local rules.
Do I need to change my injection sites?+
No. The sites and the rotation are the same, and keeping your existing pattern is better than starting a fresh one. Only the device and the numbers around it change.
Which numbers actually change?+
The missed-dose window, the room-temperature allowance and the minimum gap between doses when you move your injection day. Write all three on the new carton, because the old ones are what will come to mind first.
How much notice does the pharmacy need?+
Ask before your last dose of the old medicine. A switch is a new product and often a new authorisation, and you want any gap between the two to be a chosen interval rather than a paperwork delay.
Why does the new medicine seem weaker in the first month?+
You are comparing a starting dose with the maintenance dose you had reached. It is not a like-for-like comparison, which is why the first month is a poor moment to judge the switch.