GLP-1 Dose Calculator: Switching Between Medications
Where the label starts you on the new medication, and why no equipotency conversion between these drugs exists.
Read this first. There is no published equipotency between semaglutide, tirzepatide and liraglutide. No conversion table exists because the trials that would produce one have not been run. What this page shows is where the label starts each drug, and what prescribers commonly do when someone moves across. It is not a dose recommendation and it is not a substitute for the conversation with the person writing your prescription.
There is no direct milligram-to-milligram conversion when switching between semaglutide (Ozempic/Wegovy) and tirzepatide (Mounjaro/Zepbound). Because semaglutide is a selective GLP-1 receptor agonist and tirzepatide is a dual GIP/GLP-1 receptor agonist, gastrointestinal tolerance built on one medication does not transfer to the other. Official FDA prescribing guidance requires starting at the lowest label starting dose (2.5 mg weekly for tirzepatide; 0.25 mg weekly for semaglutide) with a 7-day washout from your last injection to avoid severe nausea, vomiting, or pancreatitis.
The dose you are on now, not the one you are aiming for.
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The titration path from there
These are the label's steps. Prescribers hold people longer at a step all the time, usually for tolerability. Moving faster than this is what produces the nausea stories.
GLP-1 Medication Switching & FDA Starting Doses Reference Table
If you are switching medications due to insurance formulary exclusions, supply shortages, or reaching a weight plateau, here is how standard FDA clinical protocols structure the transition:
| Current Medication & Dose | Switching To | FDA Starting Step | Clinical Protocol & Timing Guidance |
|---|---|---|---|
| Ozempic 0.25 mg – 2.0 mg weekly (Semaglutide) |
Mounjaro or Zepbound (Tirzepatide) |
2.5 mg weekly | Wait 7 days after your final Ozempic injection. Standard protocol requires initiating tirzepatide at 2.5 mg for 4 weeks before stepping up to 5.0 mg. Some prescribers transition patients on 2.0 mg Ozempic to 5.0 mg Mounjaro if tolerated with zero GI adverse events, but label starting dose remains 2.5 mg. |
| Wegovy 0.25 mg – 2.4 mg weekly (Semaglutide) |
Zepbound or Mounjaro (Tirzepatide) |
2.5 mg weekly | Wait 7 days after last Wegovy shot. Do not jump straight to 7.5 mg, 10 mg, or 15 mg tirzepatide; tirzepatide's additional GIP agonism creates severe nausea and gastric distress if not introduced gradually. |
| Mounjaro or Zepbound 2.5 mg – 15 mg weekly (Tirzepatide) |
Ozempic or Wegovy (Semaglutide) |
0.25 mg weekly | Wait 7 days after last tirzepatide dose. Even patients coming off maximum 15 mg tirzepatide generally restart at 0.25 mg (or 0.5 mg maximum under direct clinician oversight), because semaglutide's GLP-1 receptor binding affinity is notably different. |
| Compounded Semaglutide Syringe units (e.g. 10–100 units) |
Compounded Tirzepatide (Syringes / Vials) |
2.5 mg equivalent (25 units at 10 mg/mL) |
Never match syringe unit markings across different medications or vial strengths. Compounding pharmacies formulate tirzepatide at various concentrations (10 mg/mL, 20 mg/mL). Always calculate the exact syringe mark using our tirzepatide units calculator. |
| Saxenda 0.6 mg – 3.0 mg daily (Liraglutide) |
Wegovy or Ozempic (Semaglutide) |
0.25 mg weekly | Administer your first weekly semaglutide dose 24 hours after your last daily Saxenda injection. Transitioning from a daily to a weekly peptide requires resetting the titration ladder to 0.25 mg. |
| Rybelsus 3 mg, 7 mg, 14 mg oral daily |
Ozempic (Subcutaneous weekly) |
0.5 mg weekly (from 14 mg) 0.25 mg weekly (from 7 mg) |
Per FDA Rybelsus label instructions: Patients taking oral Rybelsus 14 mg daily can transition directly to Ozempic 0.5 mg SubQ weekly. Take the first subcutaneous injection on the day following the last oral tablet. |
Why there is no conversion table
People expect a chart that says 1 mg of semaglutide equals some number of milligrams of tirzepatide. That chart does not exist, and the reason is not laziness.
Semaglutide is a GLP-1 receptor agonist. Tirzepatide acts on GLP-1 and GIP receptors. They are not the same drug at different strengths, they are different mechanisms with different side effect profiles and different tolerability curves in the same person. A dose you tolerate well on one can be miserable on the other, in either direction.
Head-to-head trials measured outcomes, not dose equivalence. Nobody has run the study that would let anyone publish a conversion, so anyone who hands you one made it up.
What prescribers actually do
The common case: restart at the bottom
Most prescribers restart the new drug at its label starting dose and titrate up from there, regardless of where you were on the old one. It is slower and it is frustrating if you were already at a high dose, but it is the approach with the safety data behind it.
The faster case: start one step up
Some prescribers will begin a step above the lowest for someone who was tolerating a high dose of the previous drug with no significant gastrointestinal effects. This is a clinical judgement about your specific history. It is not something to decide from a web page, and it is not something a compounding pharmacy can decide for you either.
Either way, the gap matters
If several weeks passed between the last dose of the old drug and the first of the new one, the tolerance you built is gone. Prescribers generally treat a long gap as starting fresh.
What changes when you switch
Your injection day can move
Both weekly drugs are once a week on any day you pick, so a switch is a natural moment to move to a day that suits you better. Moving to Saxenda means moving to daily injections, which is a bigger change in routine than people expect.
Your supply math changes
Different concentrations, different pen sizes, different refill intervals. Recalculate what you need with the supply calculator before you run out mid-switch.
Side effects can reset
The nausea that faded on your old medication may return at the start of the new one, because the adaptation is drug-specific. This is expected and usually temporary.
Common questions
- I am on 2.4 mg Wegovy. What Zepbound dose is that?
- There is no equivalent. The Zepbound label starts everyone at 2.5 mg weekly. Some prescribers begin at 5 mg for someone who tolerated a high semaglutide dose well, but that is a judgement about you, not a conversion of the number.
- What dose of Mounjaro corresponds to 1 mg of Ozempic?
- There is no direct equivalent. Under FDA guidance, patients switching from 1 mg Ozempic to Mounjaro restart at 2.5 mg weekly for 4 weeks. In select clinical cases where patients demonstrated complete GI tolerance, prescribers may consider starting at 5 mg, but starting at 2.5 mg remains the standard protocol.
- Do I have to re-titrate from the beginning?
- Usually yes. The tolerance you built is largely specific to the drug you built it on, particularly moving between semaglutide and tirzepatide, which act on different receptors.
- How long should I wait between the last old dose and the first new one?
- For two weekly medications, prescribers commonly start the new one on the day the next old dose would have been due, so one week. That is a question for your prescriber, not a rule you can read off a page.
- How do I switch from Saxenda to Wegovy or Ozempic?
- Because Saxenda (liraglutide) is taken daily while Wegovy/Ozempic (semaglutide) is taken weekly, administer your first 0.25 mg semaglutide injection 24 hours after your last daily Saxenda dose. You must begin at the 0.25 mg starting dose rather than jumping ahead.
- Can I use the same syringe units when switching compounded medications?
- Never. Syringe units depend entirely on the specific concentration (mg/mL) prepared by your compounding pharmacy. 20 units of semaglutide at 2.5 mg/mL is 0.5 mg, whereas 20 units of tirzepatide at 10 mg/mL is 2.0 mg. Always convert using the actual vial concentration.
- Is switching because of a shortage different?
- The dosing considerations are identical. The practical difference is that shortage switches often happen with little notice, which is exactly when people are tempted to guess at a conversion. Do not.
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