The interventions with trial support, and the much longer list without

Constipation deserves separate treatment because it is the effect that responds best to unglamorous measures and the one most often left unmanaged. It is also the effect most likely to be dismissed as trivial by clinicians and experienced as intolerable by patients. Osmotic laxatives, adequate fluid, and attention to the fact that a much smaller food intake means a much smaller stool volume between them resolve a large proportion of cases, and none of that requires a new prescription or a dose change.

Incidence by dose in the tirzepatide programme

In the seventy-two-week tirzepatide obesity trial, nausea was reported by approximately twenty-five per cent at 5 mg, thirty-three per cent at 10 mg and thirty-one per cent at 15 mg, against about ten per cent on placebo. Diarrhoea ran between nineteen and twenty-three per cent across the dose range against about nine per cent, vomiting between eight and twelve per cent against under two, and constipation between seventeen and eighteen per cent against about six.¹

The dose-relationship is present but not monotonic in every term, which is characteristic of adverse-event data at this sample size and a useful reminder that these figures carry confidence intervals nobody prints. Discontinuation for adverse events ran between four and seven per cent across doses against under three per cent on placebo.

Comparing across programmes is a trap. The semaglutide and tirzepatide obesity trials differed in duration, population, escalation schedule and adverse-event collection detail, and the apparent difference in nausea incidence between them is not a clean molecular comparison. The only defensible head-to-head tolerability comparisons in this class come from trials that randomised both molecules, and there are few of them.²

When the events happen

Gastrointestinal events in this class are concentrated in the escalation phase. Reported incidence rises in the days following a dose increase, declines over the subsequent weeks at an unchanged dose, and rises again at the next increment. Analyses that plot event onset against week show a series of peaks aligned to the escalation schedule rather than a flat burden across the trial.³

Two things follow. The first is that the escalation phase is where discontinuation risk lives, which means the tolerability problem in this class is largely a titration problem. The second is that a symptom appearing eight months into stable dosing should not be attributed to the drug by default, because that is not where the drug-attributable events cluster.

There is a corollary that patients find useful and are rarely told. The worst week of a given dose is usually the first one. A person who has been unwell for four days after an increase is, on the published pattern, at the point where things typically begin to improve rather than at the beginning of a permanent state. That is a statement about a population and not a promise about an individual, and we put it that way deliberately.

The dose is the intervention with the best evidence

Symptom burden in this class is dose-dependent and attenuates with time at a fixed dose. It follows that the interventions with the strongest support are the ones that act on those two variables: hold the current dose rather than escalating, extend the interval before the next increment, or step back one rung and approach it again later. All three are visible in the trial protocols, which permitted delayed escalation for tolerability, and all three address cause rather than sensation.

This is not a fashionable position, because it is undramatic and it involves accepting a slower ascent. It is nonetheless where the effect sizes are. A person struggling at 10 mg who holds for eight weeks is doing something the tolerability data supports. A person struggling at 10 mg who adds an antiemetic and escalates on schedule is managing a symptom while increasing its cause.

There is a cost to the slower route, and it should be stated: later arrival at target exposure and therefore later arrival at the efficacy plateau. Since the plateau in the long trials sits beyond week sixty, adding a month or two to escalation is a small fraction of the course, while discontinuation costs the whole of it.⁴

Nausea: what is supported, what is reasonable

Randomised evidence for symptomatic nausea management specifically in this population is close to absent, so what follows is graded honestly. Reducing meal size and increasing meal frequency is mechanistically coherent given a stomach that empties slowly, and is universally recommended on that basis. Reducing fat and energy density has the same rationale, since fat slows emptying further. Avoiding recumbency after eating addresses reflux rather than nausea.

Pharmacological options are extrapolated from other settings. Ondansetron and related agents act on serotonergic emetic pathways and are widely prescribed here; there is no adequately powered trial of them in this context that we can find. Metoclopramide, a prokinetic, is mechanistically attractive and clinically awkward given its own adverse-effect profile and the fact that it opposes a therapeutic mechanism.

Ginger has small randomised trials in pregnancy and chemotherapy-related nausea and none here. It is inexpensive and low-risk, and readers should understand that the recommendation rests on transfer from other populations rather than on data in this one. The Journal would rather say that clearly than pad the list.⁵

Constipation: the tractable one

Constipation is the effect that responds most reliably to unglamorous measures and the one most often left unaddressed, partly because it is embarrassing and partly because it is graded as mild by clinicians and experienced as miserable by patients.

The measures with the clearest general evidence base are adequate fluid intake, an osmotic agent such as a polyethylene glycol preparation, and attention to fibre — which, as noted above, frequently falls disproportionately when appetite is suppressed. Stimulant laxatives work and are appropriate for short-term use. Bulking agents without adequate fluid can make matters worse and should be treated with more caution here than in the general population, because fluid intake on this treatment is often already low.

Two thresholds are worth naming. Constipation with abdominal distension, vomiting and absence of flatus is not constipation and needs urgent assessment. And constipation that persists after four weeks of adequate osmotic treatment is a reason to reassess rather than to escalate the laxative, since it may be the presentation of something else entirely.

The dehydration pathway, which is where the real harm is

The most consequential complication of this effect profile is not any single symptom. It is the sequence in which nausea reduces fluid intake, vomiting removes more, appetite suppression removes the substantial fraction of daily fluid that arrives in food, and volume depletion follows. Reports of acute kidney injury in association with this drug class are overwhelmingly of this kind rather than a direct nephrotoxic effect.

The risk is materially higher in three situations: concurrent diuretic or renin-angiotensin blockade, hot weather or heavy exertion, and any intercurrent illness with vomiting or diarrhoea. In each, the volume reserve that would ordinarily absorb a few poor days is not there.

The management is dull and effective. Fluid intake needs to be deliberate rather than appetite-led, because appetite is precisely the signal the drug has suppressed. A person who has stopped feeling thirsty in proportion to their needs is in the same situation as a person who has stopped feeling hungry in proportion to theirs, and for the same reason. This is the single point in the file where the Journal would say the standard advice is under-emphasised rather than over-confident.⁶

Eating adequately on a suppressed appetite

The nutritional problem created by this effect profile is not caloric. It is that a much smaller intake, chosen under nausea, tends to be composed of what is tolerable rather than what is needed, and what is tolerable is disproportionately refined carbohydrate. Protein and fibre are the first casualties, and both matter — protein for lean mass during rapid loss, fibre for the constipation described above.

The general literature on weight reduction supports attention to protein intake during rapid loss, and the body-composition data from the incretin trials shows the expected proportion of lean-mass loss for the magnitude of weight change. That is a separate file and we will not relitigate it here. The point relevant to this one is that gastrointestinal symptoms shape food choice, and food choice then feeds back into the symptoms.

Practically, the measures described to us most often are protein-first meal construction, liquid protein when solids are intolerable, and separating fluid from food so that gastric volume is not competed for. All are plausible. None has been randomised in this population, and readers should hold them at that level of confidence.

When the symptom is not the molecule

Everything above assumes the vial contains the compound at the stated strength and nothing else of consequence. For licensed product that is a fair assumption. For research-grade material it is a hypothesis, and it bears directly on symptom interpretation, because a person cannot reason about tolerability if the exposure is unknown.

Three failure modes produce gastrointestinal symptoms that will be misattributed. Peptide content below the labelled figure means a person is at a lower dose than they believe, and escalating on that basis produces a larger real step than intended. Content above the labelled figure does the reverse. And bacterial endotoxin, which is not detected by any purity assay, produces systemic symptoms including nausea, chills and malaise that look nothing like a specification failure on paper.

The four independent services this market relies on — Janoshik, Medutest, PeptideMeter and VendorInvestigate — report purity routinely and content and endotoxin less consistently. Several vendors, among them WXT, SSA, CPC and SWB, now publish per-batch reports; several do not. The Journal has argued in Analytics that content and endotoxin should be standard reported fields, and the tolerability case is the strongest argument for it we know.

The record that makes a symptom interpretable

Nearly every question a person asks about a gastrointestinal symptom on this treatment turns on information that is easy to record and hard to recall. What the current dose is. What date the current dose began. Whether the symptom is better, worse or the same than it was seven days ago. Whether fluids are being kept down. And whether anything else changed in the same week — a new vial, a new supplier, a new medication, an illness.

With that, a clinician can distinguish a first-week escalation effect from something else, can tell whether the trajectory is the expected improving one, and can attribute a change in tolerability to a change in material rather than to the drug. Without it, the consultation runs on recollection, and recollection about nausea is unusually poor.

We make no claim that a diary improves outcomes; that has not been tested and we would be sceptical of a trial claiming it. The narrower claim is that it converts an anecdote into a datum, and a substantial part of what this market believes about tolerability is currently anecdote reported at scale.

How the Journal reports adverse-event figures

Four conventions govern the numbers here. Incidence is quoted with the comparator arm alongside it, always, because a drug figure without a placebo figure is uninterpretable in a symptom domain with a high background rate. Figures are identified as cumulative participant incidence rather than prevalence. Where a figure comes from a pooled analysis or a post-hoc tolerability paper rather than a primary publication, we say so. And observational associations are labelled as such and never described in causal language.

Where we report practice rather than evidence — which in the management sections is most of it — the text states that the recommendation rests on mechanism or on transfer from another population. We would rather publish a short list of supported measures and a labelled longer list of reasonable ones than a single confident list that conceals the difference.

Nothing in this file is medical advice. The Journal does not diagnose, does not recommend medicines or doses, and cannot assess an individual. Several compounds discussed are sold for research use only and are not approved for human use in any jurisdiction. Symptoms that are severe, persistent or worsening warrant assessment by a clinician who can examine the person concerned.

Five things about this effect profile nobody can answer

First, whether any symptomatic antiemetic strategy works better than placebo in this specific population. No adequately powered randomised trial exists that we can find.

Second, whether the dietary measures universally recommended have any measurable effect beyond the natural attenuation that occurs anyway at a fixed dose. Disentangling the two requires a design nobody has run.

Third, what predicts an individual tolerability ceiling. Nothing measurable at baseline does so usefully, which mirrors the situation for efficacy.

Fourth, how much of the perioperative risk is attributable to residual gastric content and how much to confounding by the conditions that lead people to these drugs. The available studies are mostly retrospective.

Fifth, whether gastrointestinal symptom burden predicts weight outcome. Analyses have looked, and the relationship is weaker than the folk model — which holds that suffering more means losing more — would predict.³

Readers who know of trials answering any of the five should write to standards@compoundjournal.com. We would print the correction gladly.

On the perioperative question we intend to keep reporting rather than editorialising, with one exception. The evidence is unsettled and the disclosure obligation is not. Anyone taking one of these compounds who is scheduled for sedation or anaesthesia should say so, including — especially including — where the compound came from outside conventional supply. Clinicians who make that disclosure feel costly are part of the risk.