The first thing to establish is which rulebook applies. Each product has its own written instruction for a missed injection, and the two are not the same instruction. A transition means the rule changes on a specific date, and a gap deliberately placed between the last dose of one and the first of the other is not a missed dose at all.
Two rules, measured from opposite ends
The tirzepatide labeling measures forward from the injection that was missed. A dose can be given as soon as possible within four days, or 96 hours, of the missed dose. Past that, the missed dose is skipped and the next one is given on the regular day.
The semaglutide injection labeling measures backward from the next injection that is due. If one dose is missed and the next scheduled dose is more than two days away, the missed dose is given as soon as possible. If the next scheduled dose is less than two days away, the missed dose is not given, and dosing resumes on the regular day of the week.
Those two instructions can point in opposite directions on the same calendar day, which is why the answer depends on which product the person was actually taking that week. Someone mid-transition who applies the old rule to the new product is answering a question that was never asked.
Because the two products carry different missed-dose windows, it helps to understand how else they diverge before a transition, and a plain comparison is the quickest way in. The telehealth field offers these unevenly: Ro, LifeMD and Henry Meds present their own programs, while HealthRX publishes a Wegovy vs Zepbound guide that lays the two schedules and dose ranges side by side. Knowing where the products differ makes the change in rulebook on the switch date less of a surprise.
The rule that has no counterpart
One instruction on the semaglutide side deserves separate attention. If two or more consecutive injections are missed, the labeling directs reinitiating dosage escalation at a lower dosage, specifically to reduce the risk of gastrointestinal adverse reactions. A fortnight away from the drug is treated as a reason to climb again rather than resume where the schedule stopped.
The tirzepatide missed-dose instruction contains no equivalent sentence. That absence is not permission to resume at any dose after a long gap. It means the decision sits with the prescriber rather than with a printed rule, and the underlying logic is the same on both molecules: tolerability is built by continued exposure, and it fades when exposure stops.
The semaglutide tablet form has a third instruction again. A missed tablet is skipped, and the next is taken the following day. Anyone moving between forms as well as between molecules is holding three sets of instructions.
A transition interval is a plan, not a lapse
The tirzepatide labeling states that coadministration with any GLP-1 receptor agonist is not recommended, which is why the last dose of one product and the first of the other are placed deliberately rather than allowed to overlap. That placement is a prescribing decision. It depends on the last dose taken and when it was taken, and it is written down before the transition rather than worked out during it.
The practical consequence is that a blank week on the calendar during a switch has two possible meanings. Either it was the planned interval, in which case nothing has gone wrong, or it was an unplanned gap on top of the planned one, in which case the schedule the prescriber wrote no longer describes what happened. Reporting which of the two occurred is more useful than reporting that a dose was missed.
What different gaps change
| Situation | Which instruction governs | What to raise |
|---|---|---|
| Injection missed while still on the previous product | That product’s own missed-dose instruction | Whether the transition date still holds |
| Injection missed in the first weeks of the new product | The new product’s instruction, from the day the switch took effect | Whether the four-week initiation clock is affected |
| The planned interval between products | Neither, it is the prescriber’s plan | Nothing, unless it lengthened unexpectedly |
| Two or more consecutive injections missed | Escalation is reconsidered rather than resumed | What dose to restart at, and at what pace |
| A late shipment or denied refill | Supply problem, not an adherence problem | The cause, so the fix matches it |
| Doses spaced out to make a supply last | Outside every labeled allowance | Cost, before it becomes a dosing decision |
Doubling up is not in either document
The instinct to compensate for a lost week by giving extra appears nowhere in either prescribing information. Both labels handle a missed dose by giving it inside a window or skipping it, never by adding it to another. A doubled injection is a larger dose that no one prescribed.
Interruption during a switch is not a neutral event
In STEP 4, participants who reached the 2.4 mg semaglutide maintenance dose over a 20-week run-in were randomized to continue or to switch to placebo; from week 20 to week 68 the continuing group changed by 7.9 percent while the placebo group gained 6.9 percent. In the STEP 1 extension, participants regained roughly two-thirds of their prior weight loss in the year after withdrawal.
Those trials studied planned discontinuation rather than a missed week. What they establish is that exposure is doing continuous work, which is why a transition is planned tightly and why a repeated pattern of gaps is a clinical conversation rather than a scheduling one.
Most repeated gaps are supply or cost, not forgetfulness
Missed weeks are logged as adherence problems far more often than they are one. Prior authorization lapsing at the turn of the year, a formulary change, a backorder, or a shipment held in transit all produce identical blank squares and all need a different response.
How a service behaves during a gap is the clearest signal of what it is. A practice with the chart can decide whether to bridge, hold or restart lower. What a compounded GLP-1 provider does when a shipment is late, and whether a clinician rather than a support queue makes that call, is worth asking about before a transition rather than during one, since a switch is exactly when an interruption is most disruptive.
Compounded supply has no labeled fallback
Compounded semaglutide and tirzepatide are not FDA-approved products, and their preparations are not covered by either manufacturer’s prescribing information. There is no labeled missed-dose window for them, because there is no label. Concentrations differ between pharmacies, so a gap in a compounded supply cannot be reasoned about using an approved product’s instruction, and the prescriber needs the exact strength and source in order to advise on it.
Frequently asked questions
Does the previous product’s missed-dose rule still apply during a switch?
Only for injections of that product. Each prescribing information describes its own medicine, and the two windows are measured from different reference points. Once the new product has started, its instruction governs, and applying the old one produces a timing decision the labeling does not support.
Is the gap between the two products a missed dose?
No, when it was planned. The interval between the last dose of one and the first of the other is set by the prescriber, partly because coadministration with another GLP-1 receptor agonist is not recommended. A gap becomes reportable when it turns out longer than the plan specified.
What if two or more injections in a row are missed?
The semaglutide labeling directs reinitiating escalation at a lower dosage in that situation. The tirzepatide labeling has no equivalent statement, which leaves the restarting dose to the prescriber. Either way, resuming at the previous dose after a long gap is not a decision to make alone.
Can a missed injection be made up by taking extra?
Neither label provides for it. Both offer a window in which the missed dose may be given and instruct skipping it after that, with the schedule resuming as normal. Adding a missed dose to a scheduled one creates an unprescribed larger dose during the phase when tolerability is most fragile.
Does a gap restart the four-week initiation period?
That is a prescriber’s call and depends on the length of the gap. The initiation period exists to manage tolerability before any increase, so an interruption inside it changes what the following weeks mean, and the minimum interval before an increase is not shortened to make up lost time.
Sources
- DailyMed, WEGOVY (semaglutide) injection and tablet prescribing information: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ee06186f-2aa3-4990-a760-757579d8f77b
- DailyMed, ZEPBOUND (tirzepatide) injection prescribing information: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=487cd7e7-434c-4925-99fa-aa80b1cc776b
- Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance, STEP 4. PubMed: https://pubmed.ncbi.nlm.nih.gov/33755728/
- Weight regain and cardiometabolic effects after withdrawal of semaglutide, STEP 1 trial extension. PubMed: https://pubmed.ncbi.nlm.nih.gov/35441470/
- Weight Regain After GLP-1-Based Therapy Discontinuation: Failure, Physiology, or Follow-Up Gap. PubMed: https://pubmed.ncbi.nlm.nih.gov/41909366/
- FDA, Compounding and the FDA: Questions and Answers: https://www.fda.gov/drugs/human-drug-compounding/compounding-and-fda-questions-and-answers
- FDA, BeSafeRx: Your Source for Online Pharmacy Information: https://www.fda.gov/drugs/buying-using-medicine-safely/besaferx-your-source-online-pharmacy-information
