A supply gap is a pharmacological event

An interruption in this class is not simply a pause. Because plasma concentrations decline with a half-life of roughly a week for the long-acting agonists, four weeks without a dose leaves something on the order of six per cent of steady-state exposure in circulation. Tolerability adaptations that took two months to establish substantially unwind over that period. A person resuming at their previous dose is therefore not continuing treatment; they are starting a new escalation at a rung they have not occupied for a month, and the symptom response is often indistinguishable from a first exposure.

What the withdrawal designs established

Two trials in this class were built specifically to answer what happens when treatment stops. In the semaglutide programme, participants who had escalated to the top dose over twenty weeks were then randomised to continue or to switch to placebo; those continuing lost a further eight per cent of body weight over the following forty-eight weeks while those withdrawn regained about seven per cent.¹ In the tirzepatide programme, a thirty-six-week open-label lead-in was followed by randomised continuation or withdrawal, with the continuation group losing a further five and a half per cent and the withdrawal group regaining approximately fourteen per cent.²

These are among the most informative results in the field and they are frequently over-read. What they establish is that the effect is maintained by continued exposure and reverses without it. What they do not establish, because neither design examined it, is whether a reduced maintenance dose would hold the result. The comparison was full dose against nothing.

Given that cost is the leading reported reason for stopping, a randomised comparison of full-dose against half-dose maintenance would be one of the highest-value trials nobody has run.

A gap, quantified

Residual exposure after an interruption follows from the half-life alone. For a seven-day half-life at steady state, one missed week leaves about half of accumulated concentration at the point the next dose was due, two weeks about a quarter, three weeks about an eighth, four weeks roughly six per cent, and six weeks under two per cent.

That table does most of the practical work. A single omission is a minor perturbation and the labels reflect this, generally permitting the dose to be taken within a defined window and otherwise skipped, with an explicit instruction not to double up. A gap of a fortnight leaves enough drug that resumption at the previous dose is usually uneventful. A gap of a month or more is functionally a fresh start.

The Journal notes that the labels handle the first case clearly and the third case briefly, and that the second case — the two-to-three-week gap that supply problems produce most often — is where guidance is thinnest and where the numbers above are most useful.³

Re-titration in practice

The convention after a long interruption is to resume one or two rungs below the previous dose and re-escalate on the standard interval. Clinicians described re-escalation as generally faster than the original ascent, on the grounds that a person who previously tolerated a rung is likely to tolerate it again, but there is no trial evidence for accelerated re-titration and the kinetic argument for four-week steps applies unchanged.

Two failure modes recur. The first is resuming at the previous top dose because that was the dose on the last prescription, which reproduces first-exposure symptoms in someone who has forgotten what they were like. The second is the opposite: restarting at the initiation dose after a two-week gap, which discards several weeks of adaptation for no reason.

Both are avoidable with the residual-exposure figures and a note of the date of the last injection. The Journal has come to regard that date as the single most useful piece of information a person on this treatment can keep, and the one most reliably absent when it is needed.

Supply interruption as a dosing event

In this market, gaps are usually structural rather than personal. Shortage listings, restrictions on compounded supply, price movements, customs interdiction and vendors ceasing to trade all produce interruptions that arrive without notice and end without warning. We have documented gaps of one to eleven weeks arising purely from supply, in people who missed no dose voluntarily.

The practical consequence is that anyone dependent on a single source is also dependent on that source for the continuity of their titration. Several people described re-escalating three times in a year for reasons that had nothing to do with their tolerance of the drug.

There is a second-order effect worth naming. Resuming with material from a different supplier compounds the uncertainty: the person is re-escalating and simultaneously changing the actual content of the vial. Reports from Janoshik, Medutest, PeptideMeter and VendorInvestigate consistently show that nominal strength and measured peptide content are not the same quantity, and a supplier change during a re-titration makes any symptom change uninterpretable. Change one variable at a time is a laboratory principle, and it applies here.

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.

One question is worth putting to the sponsors of the next generation of these molecules, and we intend to keep putting it. Escalation is the phase in which most discontinuation occurs, and discontinuation costs the entire treatment effect. A dose-escalation trial would be inexpensive relative to a cardiovascular outcome programme and would settle the most frequently asked practical question in the field. Nobody has run one.