Semaglutide half-life and steady state
7 days modelled half-life, peaking 40 h after a dose. What that means for how long it lasts, how much it builds up, and when bloodwork is worth drawing.
- Also known as
- Ozempic, Wegovy
- Class
- GLP-1 / Metabolic
- Modelled half-life
- 7 days
- Time to peak
- 40 h
- Formulation
- Aqueous (reconstituted powder)
- Cleared per dosing interval
- 50% gone, 50% still present after 7 days
- Time to steady state
- ~35 days (about five half-lives)
- Accumulation at that cadence
- 2× a single dose
- Peak-to-trough at steady state
- 1.67×
- Regulatory status
- FDA APPROVED for T2 diabetes (Ozempic) and obesity (Wegovy). Off-label for general weight loss.
- Monitoring panel
- HbA1c, fasting glucose, lipids, amylase if abdominal pain, weight monthly.
- Before mixing
- Sealed powder tolerates room temperature in transit, but keep it refrigerated at 2–8 °C (36–46 °F) for anything beyond a few weeks, or frozen for months. Keep it dark — the carton it shipped in is doing a job.
- After mixing
- Once reconstituted with bacteriostatic water: refrigerate at 2–8 °C and use within about 28 days. The benzyl alcohol in bacteriostatic water is what buys that window — plain sterile water has no preservative, so a vial mixed with it should be treated as one sitting only. Kits are usually ten vials: only the one you mixed is on that 28-day clock — the sealed ones keep their own, much longer shelf life, so store them as powder, not as solution.
- What ruins it
- Do not freeze a reconstituted vial. Repeated freeze–thaw is one of the more reliable ways to degrade a peptide.
- Handling caveat
- General handling practice for this formulation. Your supplier’s own insert or COA overrides anything here.
Semaglutide's roughly one-week half-life is the whole reason it is a once-weekly injection, and it is unusual for a peptide. Native GLP-1 is cleared in minutes; semaglutide survives days because it is engineered to — a fatty-acid side chain binds it to albumin, and a substitution at position 8 blocks the DPP-4 enzyme that dismantles the natural hormone. The molecule is essentially a GLP-1 with a half-life problem solved.
What that means in practice is that semaglutide accumulates for about five weeks. Dosing weekly against a seven-day half-life leaves half of each dose still present when the next arrives, so the level roughly doubles before it plateaus. Two consequences follow. A dose that was comfortable in week one can be considerably less so in week four with nothing having changed but arithmetic — which is what the four-week titration steps in the approved labelling are pacing. And going the other way, stopping does not clear it quickly: appetite effects fade over weeks, not days, and the "rebound" people describe after discontinuation is partly that long tail ending.
The flip side of a long half-life is a flat curve. Dosed weekly the modelled peak-to-trough swing is small, which is why semaglutide does not produce a day-of-injection effect the way a short-acting compound does. A missed dose is also forgiving for the same reason: at this half-life, a dose taken a day or two late barely registers on the curve.
One dose
pkCurve function — a
one-compartment absorption-and-elimination model with the absorption rate fitted so the
peak lands at the published time to peak.Dosed once weekly
Charted at once weekly because that is the approved schedule for both the diabetes and the obesity indications. It is what the numbers below are indexed to, not a recommendation about frequency — that is a prescribing decision.
The arithmetic behind those numbers
fraction left after one interval = 2^(−1.00) = 0.500
accumulation ratio = 1 ÷ (1 − 0.500) = 2
time to steady state ≈ 5 × half-life = 35 days
peak-to-trough = simulated, 2.079 ÷ 1.2455 = 1.67
The accumulation ratio is a closed form; the peak-to-trough figure is not. The generator adds up enough repeated curves for the total to stop changing, then reads the highest and lowest points of the last interval — which is what steady state means in practice. The vertical axis is relative, not a concentration: the shape and the ratios carry across people, the absolute levels do not.
Interaction rules that name Semaglutide
From the app's own interaction data. Not exhaustive, and not a safety clearance — a combination that is not listed is one nobody has documented here, which is not the same as one that is fine. The full combination checker has the rest.
Never Combine GLP-1 Agonists
Combining two GLP-1 or dual GLP-1/GIP agonists dramatically increases risk of severe GI side effects, pancreatitis, and offers no additive benefit. Choose one.
What to watch: Do not combine. If switching agents, wash out first GLP-1 before starting the second.
GLP-1 + Testosterone — Essential Muscle Preservation
GLP-1 agents cause significant muscle loss without adequate testosterone support. Running TRT-dose testosterone alongside semaglutide is strongly recommended to preserve lean mass during weight loss. Resistance training is also essential.
What to watch: Body composition (DEXA preferred), Total T, HbA1c, fasting glucose, lipids.
Metformin + GLP-1 — Additive Metabolic Benefits
Metformin and GLP-1 agents work via complementary mechanisms (AMPK activation vs GLP-1 receptor) and are commonly combined in diabetes management. Both reduce HbA1c and fasting glucose. Monitor for additive GI side effects.
What to watch: HbA1c, fasting glucose, weight, GI tolerance. B12 levels with long-term metformin.
Insulin + GLP-1 agonist — Additive Hypoglycemia
A recognised clinical interaction, not a theoretical one. GLP-1 agonists lower glucose and suppress appetite, so a person on both eats less and clears glucose faster while the insulin dose stays where it was. Diabetes guidelines call for the insulin dose to be reduced when a GLP-1 is started or escalated. The same applies to tirzepatide. Severe hypoglycemia in this combination is well documented and is why it belongs to a prescriber, not to a spreadsheet.
What to watch: Glucose before and after every dose and before sleep, and a continuous monitor if one is available. Reduce insulin under medical supervision when starting or increasing a GLP-1 — never in the other order.
Never Combine GLP-1 Class Agents
Same as above — retatrutide and semaglutide both target GLP-1 receptors. Never combine two agents from this class.
What to watch: Do not combine. If switching agents, appropriate washout period required.
Cagrilintide + Semaglutide — Intended Combination (CagriSema)
Cagrilintide is specifically being developed in combination with semaglutide as CagriSema — a fixed-dose combination. Clinical trials show superior weight loss compared to either alone. This is an intended therapeutic combination, not a dangerous one. Monitor GI tolerance carefully.
What to watch: GI tolerance, weight, HbA1c, fasting glucose. This combination requires gradual titration of both agents.
The dosing rows this cadence came from
Established clinical use Reproduced from the app's entry so you can see what the chart above is indexed to. Which row applies to a particular person, if any, is a clinical decision this page does not make.
| Label | Amount | Route and frequency |
|---|---|---|
| Starting | 0.25mg/week | Weekly SubQ |
| Maintenance | 0.5-1.0mg/week | Weekly SubQ |
| Max (Wegovy) | 2.4mg/week | Weekly SubQ |
When to draw bloodwork
The panel the app records for Semaglutide is: HbA1c, fasting glucose, lipids, amylase if abdominal pain, weight monthly.. The pharmacokinetic point is the timing rather than the list: after any change, a level takes about 35 days to settle, so a panel drawn sooner measures something still moving. And because the peak-to-trough swing here is 1.67×, when in the interval you draw changes the result materially — a result without a stated draw time relative to the last dose is hard to compare with anything. Whether a result means anything is a question for the clinician who ordered it, read against the reference range your own lab printed. The lab-marker pages cover what the individual analytes measure.
Related: the interactive half-life calculator to try other cadences, and the Semaglutide reconstitution calculator.
The app draws this curve from the doses you actually logged — your dates, your cadence — and projects seven days forward from the last one.
Save this dose to your log