Numbers first: 4 mg · retatrutide.
This is a planning question. I know what my options are; I do not know how to weigh them.
What I want is the minimum viable version, which I suspect is smaller than what I would design.
How do I make this decision on evidence rather than on feel?
4 mg a week is 0.571 mg a day averaged out and 208 mg over a year — but "defensible" is not a property of the number, it is a property of where the number came from. A maintenance dose is defensible when a trial randomised people to it and reported what happened, and indefensible when it was arrived at by interpolation between two doses that were studied. So the question to ask of 4 mg is which arm it corresponds to: if a programme ran 4 mg as a maintenance level, there is an efficacy figure, a tolerability figure and a discontinuation rate attached to it. If it sits between two studied levels, everything said about it is extrapolation, and the burden of that is on whoever proposed it. The other half of the arithmetic is supply: at 4 mg a week a 10 mg vial is 2.5 weeks and you will need about 21 of them a year, which is worth knowing before the dose is settled rather than after. Maintenance doses are set by a prescriber against an individual; nothing here is medical advice.
Put another way, any reduction takes four to five weeks to express itself, so the search proceeds in months.
A downward search proceeds one step at a time with at least eight weeks at each level, because a weekly agent takes four to five weeks to reach the new steady state and then needs time for the trend to be readable.
| Week | Fraction of steady state | Trough as × dose |
|---|---|---|
| 1 | 50 % | 0.50 |
| 2 | 75 % | 0.75 |
| 3 | 88 % | 0.88 |
| 4 | 94 % | 0.94 |
| 5 | 97 % | 0.97 |
| 6 | 98 % | 0.98 |
This is why a four-week step interval is approximately, but not exactly, steady state.
If the result deteriorates on a lower dose, returning to the previous one is straightforward and does not require re-titration from the bottom provided the gap has been short.
STEP-4 and SURMOUNT-4 evaluated withdrawal rather than dose reduction, which is the limit of the direct evidence on this question.
The caveat is that dose reduction is a clinical decision and this is a description of a search strategy rather than a recommendation.
Search downward, one step, eight weeks each, on a rolling average.
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsAsk PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.