Medication level vs how you feel: what the curve can and cannot tell you

Most GLP-1 tracking apps now show a curve labeled something like “medication level”. It is a useful picture, as long as you know what it is made of.

What the curve is made of

Three things go into it:

1. Your logs: the date, time and dose of each shot or pill you record.
2. Published numbers: the half-life and time to peak of your medication, from its prescribing information. About 7 days for semaglutide, about 5 days for tirzepatide.
3. A standard model: the same simple pharmacology model used in textbooks, where each dose is absorbed, peaks, then clears at a steady rate. Each dose adds to what is left of the previous ones.

The result is shown as a share of a reference point, usually the peak your dose reaches once settled.

What it can tell you

• The shape of your week. When your level is likely highest and lowest.
• The build-up on a new dose. Why the first weeks on a dose sit lower than later ones.
• The effect of a late or missed dose on the shape of the curve, after the fact.
• A possible explanation for patterns you already notice, like food noise returning on day 6.

What it cannot tell you

• Your real blood level. Only a lab test measures that, and it is not part of routine GLP-1 care.
• How well the medication works for you. The curve looks the same for someone who responds strongly and someone who does not.
• Side effects. Nausea, tiredness or constipation depend on much more than one number.
• What to do. It is never a reason to change your dose, your timing or your schedule.

Why it is still worth looking at

The curve becomes useful when you put it next to how you feel. If you log a quick daily check-in (hunger, food noise, energy) for a few weeks, you can see whether your own pattern follows the curve. For some people it does very clearly. For others, sleep, stress or their cycle matter more. Both are useful to know, and both are worth sharing with your prescriber.

Try it

The GLP-1 level estimator shows the curve for your medication and shot day, including your first weeks on a dose. Everything is calculated in your browser.

Sources

• Prescribing information for Wegovy, Ozempic, Zepbound and Mounjaro, section 12.3 (pharmacokinetics).