Why people actually stop, in the order they actually stop

The shortage years produced an unintentional natural experiment in interrupted treatment, and its main lesson was about escalation rather than about regain. People who had been stable at a maintenance dose for months, lost access for six or eight weeks, and then resumed at the dose they had been on, frequently found the resumption far less tolerable than the original escalation had been. That is exactly what the pharmacokinetics predicts, it was widely experienced, and it was almost never explained in advance.

The arithmetic of a fortnightly schedule

For a drug eliminated with first-order kinetics, the accumulation ratio at steady state is approximately one divided by one minus the exponential of minus the elimination rate constant times the dosing interval. For a seven-day half-life given weekly, that yields a ratio of about two. Given fortnightly, the interval is two half-lives, the residual fraction at the next dose is a quarter, and the accumulation ratio falls to about one and a third.

Two consequences follow. Average concentration on a fortnightly schedule at the same nominal dose is roughly a third lower than weekly, not half, because accumulation differs. And the peak-to-trough ratio rises from modest to fourfold, so the exposure pattern is qualitatively different: the person spends part of each cycle at an exposure that would be sub-therapeutic on a weekly schedule and part at a higher peak.

What the arithmetic cannot tell you is whether that pattern is better, worse or equivalent for maintaining weight, because the relationship between exposure pattern and weight effect is not known — only the relationship between average exposure and weight effect at steady state. The modelling is solid and it answers a different question from the one people bring to it.

Resuming after an interruption is a fresh escalation

This is the most practically consequential item in the whole subject and the one least often stated in advance. Gastrointestinal tolerability to these agents develops over weeks of continued exposure and decays when exposure is removed. After four weeks without the drug, plasma concentrations are a small fraction of steady state and the tolerability accommodation has substantially reset. Resuming at the previous maintenance dose therefore presents the system with an exposure step it has not experienced for a month.

The clinical convention — resume at a lower dose and re-escalate — follows from the pharmacokinetics rather than from caution.¹ Product labelling for several agents in the class advises consideration of re-initiation at a lower dose after an extended interruption, and the threshold at which this applies differs between products, which is a detail worth checking against the specific label rather than a general rule.

The shortage period demonstrated the consequence of ignoring this at scale. Large numbers of people lost access for six to ten weeks, resumed where they had left off, and experienced nausea and vomiting considerably worse than during their original escalation. It was predictable, it was predicted by anybody who had read the label carefully, and it was almost never communicated.

Cost is the modal reason, and it is missing from the clinical literature

Analyses of pharmacy claims consistently find that persistence with these agents for weight management is poor relative to their efficacy, with a large minority of people no longer filling prescriptions within a year of starting and discontinuation concentrated in the first three months.² The pattern tracks coverage, deductible reset timing and cash price far more closely than it tracks clinical response, which is the signature of an economic rather than a therapeutic discontinuation.

Almost none of this appears in the clinical literature on withdrawal. The trials studied people who stopped because a protocol told them to, with the drug supplied free, in a population willing to be randomised. That is close to the opposite of the situation in which most discontinuation actually occurs: unplanned, unsupervised, at a time set by an insurer or a price rise rather than by a clinical assessment, and frequently without anybody being told it has happened.

The Journal reports discontinuation in both this department and The Ledger for that reason. The clinical trajectory after stopping is a Patient Notes question; why people stop is an economics question; and the two literatures currently do not speak to one another at all.

The supply interruption as a clinical event

A supply gap is a discontinuation with no notice, no plan and no taper. It differs from every other route to stopping in that it is imposed on both the patient and the prescriber, its duration is unknown at the outset, and it frequently ends as abruptly as it began. The shortage listings of recent years produced these events at population scale, and they have not been studied as a clinical exposure.

Three features make them distinctive. The patient cannot plan a maintenance strategy around an interruption of unknown length. Substitution — to a different agent, a different dose, or a compounded preparation — happens under time pressure and often without a dose-equivalence basis, since no head-to-head equivalence data exists between agents in this class. And the resumption problem described above applies in full, because the gaps were typically long enough to reset tolerability.

The Journal reported these events as they occurred and continues to think they represent the largest uncontrolled interruption experiment in the history of the class. What nobody collected was outcome data: how much weight was regained during the gaps, how many people never resumed, and what happened to the glycaemic control of those taking the drugs for diabetes rather than for weight.

When the indication is not weight

The withdrawal question changes shape when the drug was prescribed for something other than weight. In the cardiovascular outcome trial of semaglutide in overweight and obesity without diabetes, the reduction in major adverse cardiovascular events emerged over years of continued treatment, and the trial provides no information about what happens to that benefit on cessation.³ The same applies to the renal outcome data in chronic kidney disease with type 2 diabetes, where the effect on kidney disease progression was measured over a median of several years of treatment.⁴

There is no reason to expect an outcome benefit that accrues over years to persist after the exposure ends, and no trial has tested it. For a person taking the drug for glycaemic control, stopping has an immediate and measurable consequence in HbA1c over the following three months. For a person taking it for cardiovascular or renal risk, stopping has no measurable short-term consequence at all, which makes the decision harder rather than easier.

This is the situation in which the Journal thinks the withdrawal-trial coverage has done the most damage. Framing discontinuation as a weight question invites a person taking the drug for kidney disease to reason about it in the wrong currency entirely.

The first six weeks after the last injection

Exposure falls on a predictable schedule. A week after a final weekly injection roughly half the steady-state concentration remains; at two weeks a quarter; at four weeks a few per cent. Appetite returns along a curve that lags the concentration curve somewhat, and delayed gastric emptying resolves over a similar interval, so the sensation of early fullness that has been governing meal size for months disappears over about a month.

What people report, and the Journal reports it as report rather than as measurement, is that the appetite return is experienced as abrupt rather than gradual — as a threshold being crossed somewhere in the third or fourth week rather than as a smooth ramp. That is consistent with a non-linear relationship between receptor occupancy and the perceived effect, which is what the dose-response data would predict, and it is not consistent with the exposure curve alone.

Glycaemic parameters follow their own timescale. Fasting glucose responds within days to weeks; HbA1c, which reflects the preceding three months with the recent weeks weighted most heavily, will not show the full consequence of stopping for a full quarter. A panel drawn four weeks after cessation will understate the change, and this is a specific and common misreading. In the trial population with type 2 diabetes, where glycaemic control was a co-primary concern, the treatment effect on HbA1c was of the order of one and a half percentage points, which is the scale of what a cessation eventually undoes.⁵

Restarting after a long gap: what to expect

Restarting after months away is well tolerated in general and the response is broadly reproducible: people who lost weight on an agent and stopped generally lose weight again on resuming, at a similar rate. There is no established phenomenon of a diminished second response in this class, and the withdrawal trials that re-offered treatment after their observation periods did not report one.

Three practical features recur. Escalation has to start again from a low dose for tolerability reasons, which means several weeks before the previous maintenance exposure is re-established. The nausea of a second escalation is frequently reported as worse than the first, for which the Journal has seen no mechanistic explanation and would not rule out reporting bias. And the weight trajectory on restarting begins from wherever the person now is, so a second course is a longer project than the first if regain was substantial.

None of this constitutes advice about whether to restart, which is a clinical decision. It is offered as a description of what the trial reports and the correspondence describe, and readers should note that no trial has been designed to study re-initiation as its primary question.

How the Journal reports a regain figure

Four things accompany every regain number in these pages. Which withdrawal design it comes from, because an off-treatment extension and a randomised placebo switch are different experiments. Whether the lifestyle intervention continued in the arm being described. What the denominator is — regain as a percentage of body weight, as a percentage of the weight lost, or as a final position relative to original baseline, three quantities that are routinely quoted interchangeably. And the follow-up duration, because the regain curve decelerates and a figure at six months is not a figure at a year.

The third of those is where most of the misreporting happens. A statement that participants regained two-thirds is a proportion of loss; a statement that they regained eleven per cent is a proportion of body weight; a statement that they finished 5.6 per cent below baseline is a final position. All three can describe the same arm and they are not interchangeable.

Where a source we are quoting has not stated its denominator, we say that rather than inferring it. Readers who find a regain figure in these pages without its design and its denominator have found an error, and the standards desk would like to hear about it at standards@compoundjournal.com.

What this piece is not

This is reporting on a body of trial evidence and it is not advice about whether or how to stop taking a medicine. The decision to discontinue an agent prescribed for glycaemic control, cardiovascular risk or kidney disease is materially different from the decision to discontinue one prescribed for weight, and in every case it belongs with a clinician who has seen the person and knows why the drug was started.

Two further notes. Compounds sold for research use only are not approved for human use in any jurisdiction, and nothing here should be read as guidance about using them or about stopping their use. And where this piece describes what clinicians report doing about maintenance dosing, that is description of practice and not a schedule anybody should adopt from a magazine.

The Journal takes correspondence on this subject at letters@compoundjournal.com and factual challenges at standards@compoundjournal.com. Letters describing a personal experience of stopping are read with attention and are published, where they are published, as accounts rather than as evidence — a distinction this department tries hard to preserve in both directions.

Two practical items follow from the pharmacology rather than from the trials, and only two. An interruption long enough to clear the drug is long enough to reset tolerability, so resumption is a fresh escalation and should be planned as one. And a laboratory panel drawn less than three months after stopping will not yet show the full glycaemic consequence, whatever it turns out to be.