The ceiling is a tolerability finding, not an efficacy one

The approved maximum doses in this class were not set by running out of efficacy. They were set by running out of tolerability at a point where additional efficacy had already become small. Semaglutide at 2.4 mg weekly was selected over higher doses examined in earlier ranging work; tirzepatide at 15 mg sits at the top of a series in which each increment produced less than the one before. That shape — rising benefit, flattening quickly, with symptom burden that does not flatten — is the defining feature of the class and the reason the ceiling exists.

The semaglutide ladder, rung by rung

For weight management, the approved escalation runs 0.25 mg weekly for four weeks, then 0.5 mg, then 1.0 mg, then 1.7 mg, reaching 2.4 mg at week seventeen. For glycaemic indications the ladder is shorter and the maximum lower: 0.25 mg, then 0.5 mg, then 1.0 mg, with a 2.0 mg option added later on the strength of a dedicated dose-comparison study.

Two features are worth noticing. The starting dose is explicitly sub-therapeutic — 0.25 mg is a tolerability rung, not a treatment dose, and describing it as a low dose rather than an initiation dose causes real confusion. And the ratios narrow as the ladder rises: two doublings, then a 1.7-fold step, then a 1.41-fold step.

The 2.4 mg dose was selected on the basis of the phase 2 dose-ranging programme and carried into the STEP trials, where it produced a mean weight reduction of about fifteen per cent at sixty-eight weeks against roughly two and a half per cent on placebo.¹ That is the number the ladder exists to reach, and the ladder itself was never the subject of the trial.

What the protocols allowed and the labels lost

The pivotal protocols in this class permitted escalation to be delayed. In the semaglutide obesity programme, participants unable to tolerate a dose increase could remain at the previous dose and attempt escalation later; the tirzepatide programme contained comparable provisions, with defined windows and a limit on how long a participant could remain below target before being counted as not having reached it.

This matters for how the efficacy figures should be read. The mean weight reductions quoted from STEP and SURMOUNT were produced by populations in which a meaningful minority spent time below their assigned target dose. The trials therefore already contain the effect of flexible titration, and the flexible approach is not a departure from the evidence but part of how the evidence was generated.

What the labels carry forward is the ladder. What they largely omit is the permission. A prescriber who reads only the label sees a fixed calendar; a prescriber who reads the trial documentation sees a calendar with a documented escape valve. The Journal has raised this with two regulatory affairs specialists, both of whom regarded it as a known and unglamorous gap in how trial conduct is translated into prescribing information.²

Stepping down is part of the method

Dose reduction in this class carries a stigma that the pharmacology does not justify. Because the ceiling is set by tolerability and tolerability varies severalfold between people, the only way to find an individual ceiling is to move until it is reached and then move back. A reduction is the second half of that measurement.

There is a practical detail worth stating. Reduction takes effect on the same kinetics as escalation, which means the relief is not immediate: a person dropping from 15 mg to 10 mg is still carrying substantial exposure from the higher dose for a fortnight, and concluding after five days that the reduction has not helped is premature.

There is also an arithmetic trap for vial users. Halving a dose halves exposure at steady state, but the transition takes three to four weeks, and during that transition the person is at neither dose. Anybody adjusting downward to escape a symptom should expect the answer to arrive on a three-week timescale, not a three-day one.

Target dose against maximum dose

The SURMOUNT-1 results are the clearest available illustration of a flattening curve. At seventy-two weeks the mean weight reductions were approximately fifteen per cent at 5 mg, nineteen and a half per cent at 10 mg and twenty-one per cent at 15 mg, against about three per cent on placebo.³ The step from 5 mg to 10 mg bought roughly four and a half percentage points; the step from 10 mg to 15 mg bought roughly one and a half.

Set against that, gastrointestinal adverse events and discontinuation for adverse events both rose across the dose range. The question of whether the top rung is worth climbing is therefore a genuine trade-off rather than a formality, and it will have different answers for different people.

The Journal has no view on where any individual should stop. We have a strong view on how the question should be framed: not as whether to reach the maximum, but as what the next increment is expected to add and what it is expected to cost. Framed that way, a decision to remain at an intermediate dose is a defensible reading of the dose-response data rather than a compromise.

Above the approved maximum

There is no published sustained-dosing human data above the approved maxima for the current generation of incretin agonists. Higher doses were examined in earlier ranging work and in some cases in dedicated comparisons; the pattern was consistently more adverse events and modest incremental efficacy. The dedicated semaglutide dose-comparison study in type 2 diabetes, which compared 2.0 mg against 1.0 mg weekly, found a further HbA1c reduction of a few tenths of a percentage point with a broadly comparable safety profile — a real but small gain at a doubling of dose.⁴

That is the shape of the evidence at the top of the curve: real increments, shrinking fast. Extrapolating it upward past the studied range is not supported, and the Journal declines to speculate about doses for which no human exposure data exists.

We report that off-label escalation occurs because it does and because pretending otherwise makes coverage useless. We do not report it as a strategy, and readers should note that research-use-only material is not approved for human use in any jurisdiction and carries no assurance of identity, content, sterility or endotoxin limit.

The shape of the curve, stated numerically

Across the programmes the exposure-response relationship for weight is approximately log-linear over the lower and middle range and flattens above it, while the relationship for gastrointestinal adverse events is closer to linear in dose and does not flatten in the same range. That divergence is the ceiling.

In glycaemic endpoints the flattening is even more pronounced. HbA1c reduction in the tirzepatide diabetes programme differed by roughly a quarter of a percentage point between the 5 mg and 15 mg arms in the head-to-head against semaglutide, which is a small difference against a threefold dose range.⁵ For a person whose objective is glycaemic control rather than weight, the argument for the upper rungs is correspondingly weaker.

The general point is that the class has two dose-response curves running in parallel and only one of them flattens. Any discussion of escalation that quotes the efficacy curve without the tolerability curve is quoting half a graph, which is how the top of the ladder came to be treated as an obvious destination.

A dose is a number about a vial

Everything above assumes the dose administered is the dose intended. For licensed pens that assumption is reasonable. For research-grade lyophilised powder it is an assumption that should be examined, because a titration schedule built on an unreliable starting figure propagates the error through every subsequent rung.

Two distinct quantities are involved. Chromatographic purity describes the proportion of peptide-related material that is the intended peptide. Peptide content describes what fraction of the vial mass is peptide at all, the remainder being counter-ions, residual solvent, water and excipient. A vial can be ninety-nine per cent pure and contain substantially less peptide than its label states, and content is the figure that determines a dose.

Of the four independent services this market relies on, all report purity and only some report content routinely. Janoshik, Medutest, PeptideMeter and VendorInvestigate have each published results in which nominal and measured strength diverged. The Journal has argued in Analytics that content should be reported as standard, and we repeat it here for a titration-specific reason: without it, the arithmetic of a step is being performed on a number nobody has measured.

Non-standard concentrations and the errors they cause

Compounded and grey-market preparations are frequently supplied at concentrations that do not correspond to any licensed presentation. That is not in itself a quality problem, but it removes every mental shortcut a person may have acquired, and it interacts badly with escalation.

The recurring error is arithmetic rather than clinical: a person who has learned that a particular volume equals a particular dose changes vial, keeps the volume, and changes the dose without intending to. We have seen this reported in both directions and at magnitudes exceeding a full rung on the ladder.

Two habits protect against it. Recompute the volume-to-dose conversion whenever the vial changes, from the stated content and the reconstitution volume, rather than carrying the old figure forward. And write the result down somewhere attached to the vial, because the calculation is easy and the recall is not. The Journal covers the underlying arithmetic in the injection-practice file; the point here is that changing vials mid-titration converts a titration decision into a units problem, and units problems are where the largest errors in this field occur.

How the Journal reports dose figures

Three conventions govern the numbers in this file. Weight-change figures are quoted with the estimand named, because the treatment-policy and trial-product analyses in the obesity programmes differ by two to three percentage points and secondary coverage habitually mixes them. Doses are quoted as the weekly amount, not as a pen volume or a unit count, because volume and units depend on concentration and concentration varies. And where a figure derives from a responder analysis rather than a primary endpoint, we say so.

Where we describe practice rather than evidence, the text says so explicitly. A substantial part of what is known about titration in this class is craft knowledge held by clinicians, and reporting it is legitimate journalism. Presenting it as trial data is not.

Nothing in this file is medical advice. The Journal does not recommend doses, schedules, products or suppliers. Several compounds discussed here are sold for research use only and are not approved for human use in any jurisdiction. Decisions about treatment belong with a licensed clinician who has examined the person concerned.

Five things about titration nobody can currently answer

First, the optimal escalation interval. No adequately powered randomised comparison of intervals at a fixed target dose exists for any molecule in this class.

Second, the optimal hold duration for a person who has not adapted at four weeks. Practice ranges from four to twelve weeks on no comparative evidence at all.

Third, the lowest maintenance dose that preserves a result. The withdrawal trials compared full dose with nothing.

Fourth, whether tolerability at one rung predicts tolerability at the next. Clinicians assume it does, plausibly, and the published dose-ranging data is not analysed in a way that answers the question.

Fifth, whether any measurable baseline characteristic predicts the ceiling. Nothing published does so usefully, which mirrors the situation for efficacy: mean behaviour in this class is well characterised and individual variation is not.⁶

The Journal lists these not as a complaint about researchers but as a map of where confident advice is currently outrunning its evidence. Anyone offering a precise answer to any of the five is offering an opinion, and should be read as doing so.

What follows this file in the department is the other half of the same problem: not how to raise the dose, but what to do about the symptoms that decide whether raising it is possible at all. Titration and tolerability are one subject examined from two ends, and the second end is where most people actually live.