[Explainer] half-life is 168 hours. that is why your injection day barely matters.
Every week somebody asks whether Tuesday is better than Sunday, and every week the answer is buried under anecdote.
Semaglutide's terminal half-life is roughly 168 hours — about a week. Practical consequences:
- Steady state takes 4–5 weeks per dose step. What you feel in week one of a new dose is not what that dose does.
- Peak-to-trough variation within a dosing interval is modest once you are at steady state. You are not on a rollercoaster, you are on a plateau with a gentle ripple.
- Which day you pick is irrelevant pharmacologically. Which day you remember is extremely relevant, because interval consistency is the only part of the schedule that has an effect.
Time of day is a tolerability preference, not a pharmacology decision. Evening dosing means you may sleep through the early GI window. That is a real reason and it is not a pharmacokinetic one.
best — the order this archive was captured in
The one refinement I would add: the subjective experience is not flat even when the plasma level nearly is, because gastric emptying effects are more pronounced in the first few days after a dose than at the end of the interval.
So people reporting a "good week and a flat week" are not imagining it — they are describing a motility effect on top of a fairly stable concentration. Two different curves, one week.
this is the correction the post needed and i will fold it into the wiki version. concentration flat, effect not flat.
this explains why moving to friday evenings worked for me. it did not change the drug, it moved the worst two days onto a weekend.
sunday 8pm, 61 weeks straight, same logic in reverse. consistency is the whole trick and the day is arbitrary.
so the correct answer to "which day" is "the one you will not forget"?
exactly that. it is the only variable in the question that has an effect size.
Linking this from the c/semaglutide wiki. The 4-to-5-week steady state point is the one that would prevent the most posts if it were better known — people judge a dose step at day nine and conclude it is not working.
and it is the reason twice-weekly splitting has a plausible rationale and almost no outcome data. with a week-long half-life the PK argument for splitting is weak to begin with.
week two, nothing happening, and this thread has explained why better than anything else i have read. edit: week five now, something is happening.
168 hours is wrong, it is 7 days
168 hours is 7 days.
...yes it is. leaving this up as a monument.
- 1The one refinement I would add: the subjective experience is not flat even…6 comments in this branch · started by u/gastric_emptying_g