Seasonal use, holiday use, and the honest state of the evidence

The word microdosing has migrated into this field from an unrelated context and carries an implication it has not earned: that a small dose produces a distinct and desirable class of effect. For these agents there is no evidence of any such thing. A low dose produces a smaller version of the same effect, with the caveat that the dose-response relationships for weight, for glycaemia and for gastrointestinal tolerability have different shapes, so the ratio of benefit to burden does change across the range. That is worth knowing and it is not what the borrowed word implies.

The physiology was described before the drugs existed

The homeostatic response to weight loss was characterised in a study that predates this drug class and remains the clearest account of it. After a substantial diet-induced reduction, circulating leptin fell and remained suppressed, ghrelin rose and remained elevated, satiety hormones including peptide YY and cholecystokinin fell, and subjective hunger was significantly greater than baseline — and all of these persisted at twelve months, long after active dieting had ended.¹

Alongside the hormonal changes sits a reduction in resting energy expenditure larger than the loss of metabolically active tissue predicts, an effect usually termed adaptive thermogenesis. Its magnitude and persistence are contested, but in the most extreme documented cohort — participants in a televised competitive weight-loss programme followed for six years — resting metabolic rate remained substantially suppressed relative to prediction long after most of the weight had returned.²

Both findings explain regain after drug withdrawal without invoking anything specific to incretins. A drug that suppresses appetite is holding a system away from a defended state. Remove the drug and the system, which has been signalling for restoration throughout, gets what it has been asking for. That is not a drug effect; it is the condition the drug was treating becoming visible again.

What comes back, and in what proportion

The composition of regained weight is the thinnest part of this literature. None of the three withdrawal designs measured body composition after cessation. The concern most often voiced — that weight lost in a favourable fat-to-lean ratio returns in a less favourable one, so that repeated cycles progressively worsen composition — is physiologically plausible and, in this drug class, entirely unmeasured.

What exists comes from the dietary weight-cycling literature, where the picture is mixed rather than alarming: several studies find that regained weight is disproportionately fat, several find no such asymmetry, and the meta-analytic position is that weight cycling has not been shown to produce a cumulative composition penalty in humans. The Journal regards that as genuinely unresolved rather than as reassurance.

One dataset does bear on it indirectly. In the maintenance trial that randomised exercise, a GLP-1 receptor agonist, both or neither after a diet-induced loss, composition was tracked throughout, and the arms that trained retained a more favourable composition through the maintenance year.³ That is a statement about maintenance rather than about regain after withdrawal, and it is the closest thing to relevant evidence anybody has.

The dose-reduction trial that has never been run

Set the three withdrawal trials side by side and a conspicuous absence appears. All three compared a full maintenance dose against placebo. None compared a full dose against a reduced one. The comparison that the great majority of successfully treated people actually face — can I take less of this and hold what I have — has not been randomised at any dose, in any programme, for any agent in this class.

The commercial explanation is straightforward and the Journal states it without much comment: a trial demonstrating that a third of the dose maintains most of the effect would reduce the revenue per treated patient by roughly the same fraction, and sponsors are not obliged to run trials against their own interest. The regulatory explanation is that maintenance dosing falls outside the approved label question, which is whether the product is effective at the studied dose.

The result is that an enormous amount of clinical practice is being conducted on inference. What can be inferred is that the dose-response curve for weight effect flattens at the top of the range, which suggests a step down would cost less than proportionally. Whether the curve is the same shape descending as ascending is unknown, and hysteresis in either direction would not be surprising.

It is worth noting what the one head-to-head weight trial in this class did and did not do. It compared two agents at their respective licensed doses and reported the difference in weight outcome; it did not establish dose equivalence between them, and it cannot be used to convert a maintenance dose of one into a maintenance dose of the other.⁴ Pharmacies asked to substitute during the shortage period had no equivalence basis to work from, whatever the conversion tables in circulation implied.

Intermittent schedules: the evidence, stated in full

This section is short because the evidence is. The Journal has searched the trial registries and the published literature for any randomised comparison of an intermittent schedule against a standard weekly schedule for any GLP-1 receptor agonist or dual agonist, at any dose, for any indication. We have found none. We have also found no observational cohort large enough to characterise outcomes on such a schedule with the standard confounders addressed.

What exists is dose-ranging data from the phase 2 programmes, which establishes that lower average exposures produce smaller weight effects, and pharmacokinetic modelling, which establishes what average exposure and what peak-to-trough ratio a given interval would produce. Neither tells you whether a fortnightly schedule maintains weight in somebody who has already lost it, which is the question actually being asked.

An absence of evidence is not evidence of harm and the Journal does not present it as such. It is, however, the entire evidentiary position, and readers encountering confident protocols for intermittent use should know that the confidence is not coming from data. Nothing in this section is advice, and the compounds sold for research use only that appear in some of these protocols are not approved for human use.

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.⁵ 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.

The case for tapering, stated as fairly as we can

There is no withdrawal syndrome from these agents, no dependence, and no pharmacological reason to reduce gradually rather than to stop. A seven-day half-life produces its own taper: concentrations halve within a week and fall to a few per cent within a month regardless of intent. On the pharmacology alone, a planned taper accomplishes nothing that stopping does not.

The behavioural argument is different and better. Appetite returns over weeks. A person whose dose is reduced in steps experiences that return in stages, while continuing to have some pharmacological support, and has a window in which to establish eating patterns that will have to hold without the drug. A person who stops outright experiences the same return without that window. Whether the window produces better outcomes is an empirical question that has not been asked in a trial.

The Journal’s position is that the behavioural argument is worth making on its own terms and worth not dressing in pharmacological clothing. What a taper cannot do is prevent regain, since the withdrawal trials establish that ongoing exposure is what holds the weight. Presenting a taper as a way of stopping without regaining is a claim the evidence does not support in any form.

What would settle the maintenance question

The Journal’s position is that three trials would resolve almost everything currently argued about in this area, and that all three are straightforward. The first is a dose-reduction design: after a lead-in to target, randomise to full dose, one step down, two steps down, or placebo, and follow for a year with weight as the primary endpoint. It would establish the shape of the descending dose-response curve and would cost a fraction of a pivotal programme.

The second is an interval design: after a lead-in, randomise to weekly, fortnightly and three-weekly administration at the same nominal dose. It would answer the intermittent-schedule question directly and would settle whether the exposure pattern matters independently of average exposure.

The third is a taper design: randomise abrupt cessation against a stepped reduction over twelve weeks, with appetite, eating behaviour and weight measured for a year afterwards. It would test the only argument for tapering that is worth testing.

None of the three is under way as far as the Journal can establish. Readers who know otherwise should write to letters@compoundjournal.com; a registered protocol for any of them would be news in this department.

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.

Readers deciding whether to stop should be told the two things the trials do establish and the one thing they do not. Regain begins promptly and decelerates; the residual benefit at a year is real but modest; and no dataset anywhere permits a personal prediction. Any source offering an individual probability of holding weight after cessation is presenting a group mean as a forecast.