Switching GLP-1 medications: what to track
People switch between GLP-1 medications for lots of reasons — supply, cost, coverage, tolerability, or a prescriber's judgement. Whatever the reason, the switch itself creates a specific record-keeping problem, because the numbers on one product do not translate to the numbers on another.
Doses do not convert between products
This is the single most important thing to understand, and it catches people out constantly. A dose in milligrams on one GLP-1 medication is not equivalent to the same number of milligrams on another. The compounds differ, the labeled ladders differ, and the maximum labeled doses differ.
Semaglutide products run on ladders topping out at 2 mg or 2.4 mg depending on the product. Tirzepatide products run in 2.5 mg increments up to 15 mg. A person at "the top" of one is not at "the top" of the other, and there is no conversion factor you can apply yourself.
Where you start on a new product is a prescriber's decision. Most labeled schedules describe starting a new medication at its own initiation step rather than matching a previous dose, but that is a decision for your prescriber, not an inference from a chart.
What actually changes at a switch
- The dose ladder. Different steps, different increments, sometimes a different number of steps before maintenance.
- The elimination half-life. Semaglutide and tirzepatide clear at different rates, which changes the shape of the curve between injections. The Half-Life Data Table lists the published figures with an evidence tag for each.
- The delivery format. Moving between a pre-filled pen and a vial changes the arithmetic entirely — a vial adds reconstitution, concentration and syringe units. See the GLP-1 Dose Calculator.
- Cost per dose. Frequently the reason for the switch, and frequently miscalculated. Cost per dose depends on your step, not just the price of the box.
- Supply timing. Old supply and new supply rarely align neatly, and the gap is where people get stuck.
What to keep in your record through the change
The temptation at a switch is to start a fresh log. Resist it. The value of the record is precisely that it spans the change.
- The last dose of the old medication — product, dose, date. This is the anchor for everything that follows.
- The date of the switch itself, as a distinct event rather than an implied one.
- The starting step on the new product, as agreed with your prescriber.
- Any leftover supply of the old product, including its expiry — it does not stop expiring because you stopped using it.
- How the weeks after the switch went, in whatever detail is useful to you. This is the part people most often wish they had written down.
Peptide Plug handles more than one compound on the same timeline for exactly this reason: a switch is a continuation of your record, not the end of one and the start of another.
The gap between supplies
A practical point that gets overlooked. If the switch is driven by supply or coverage, there is often a gap between running out of one product and starting another. That gap is worth planning deliberately rather than discovering.
Work out the run-out date on your current supply from your actual logged doses rather than an assumed schedule — the Vial Longevity Calculator does this — and raise the timing with your prescriber before you are inside the gap rather than after.
Frequently asked
Can I convert my dose from one GLP-1 to another?
Do I start over at the lowest dose when switching?
Should I start a new log when I switch?
What do I do with leftover medication from the old product?
Will the switch change my cost per dose?
Tools for a switch
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