What is the reported incidence of constipation on a GLP-1 receptor agonist in SURPASS-3?

What I am working with: constipation · a GLP-1 receptor agonist · SURPASS-3.

I have read the primary source rather than the summary, which has left me with more questions.

I understand the headline. I do not understand the footnotes, and the footnotes look important.

How should I read this, and where are the traps?

The underlying point is that the mechanism explains the pattern. Delayed gastric emptying plus central appetite suppression produces early satiety, and early satiety plus a slowed transit produces exactly the symptom cluster people report.

Pancreatitis red flags worth memorising rather than looking up: severe, persistent epigastric pain radiating to the back, worse lying flat and better sitting forward, with nausea and vomiting that does not settle. That combination is an urgent assessment, not a dose adjustment. An isolated lipase elevation without that picture is common and usually not pancreatitis.

To be exact about it, vomiting matters mostly through its consequences. Loss of gastric fluid depletes sodium, chloride and potassium, and hypokalaemia presents as exactly the fatigue and cramping people attribute to the drug. Persistent vomiting also makes a renal panel uninterpretable, because a pre-renal picture looks like renal impairment.

Fix the fixable causes first — fluid, electrolytes, sleep, intake — before concluding that the compound is responsible.

To be exact about it, the honest framing is that this is very common, usually self-limiting, and occasionally the presentation of something that is not self-limiting at all — and the differentiating features are specific enough to be worth knowing.

Constipation outlasts the nausea because it has two causes and only one of them resolves. Gastric emptying accommodates over weeks; total intake, and therefore stool volume and the osmotic load reaching the colon, does not recover until intake does. This is why fibre alone can make it worse — you add bulk to a system that is short of water and short of motility.

Fatigue attribution is a subtraction problem. Take out the energy deficit, the dehydration, the electrolyte shortfall and the poor sleep, and what remains attributable to the drug in the trials was modest — placebo-arm fatigue rates were within a few points of active-arm rates in most of the programme. The corollary is that the fixable causes are usually the actual causes.

The prescribing information for each agent lists adverse reaction frequencies against placebo in a table, and reading that table is more informative than reading a hundred anecdotes, because it has a denominator.

The caveat that actually matters: this is pattern recognition from published data, not a clinical assessment of you. Anything severe, persistent or accompanied by systemic features belongs with a clinician the same day.

Most of this resolves. The point of knowing the pattern is to recognise the small fraction that does not.

edited 28 Jan 2025 by ines_brandt — corrected a unit error in the worked example

Timing is the most useful diagnostic feature here and it is the one most often omitted from the question.

Distinguishing an injection-site nodule from an infection: a nodule is firm, non-tender or mildly tender, not warm, not expanding, and appears within a day or two. Cellulitis is warm, tender, expanding, and often accompanied by systemic features. A sterile abscess sits between the two and is fluctuant. Warmth plus expansion plus fever is the combination that stops being a forum question.

Pooled analyses of gallbladder-related events with GLP-1 receptor agonists find a modest increase in relative risk, with the effect larger at higher doses and longer durations — consistent with a rate-of-loss mechanism as much as a direct one[1].

Write down in advance which symptoms mean stop and seek care. It is a short list and it is much easier to write when you are well.

The incidence figures are dose-related but the timing is escalation-related, and conflating the two produces most of the bad advice in this area. Adverse events cluster in the one to two weeks following each dose increase, then decay.

The telogen effluvium timing signature is the diagnostic feature: hair enters the shedding phase two to four months after the insult, so shedding that starts at month three of rapid loss and peaks around month four to five is the expected pattern. Shedding that starts in week two is not telogen effluvium and warrants a different question. In either case the follicle is not destroyed and regrowth is the rule.

The pooled gastrointestinal adverse-event rates across the STEP programme and the SURMOUNT programme are reported in the primary publications and in the FDA and EMA assessment reports, and the assessment reports are more useful because they give the placebo-arm rates alongside the active-arm rates in the same table.

A symptom diary with dates against dose steps answers most of these questions without anyone needing to guess.

edited 29 Dec 2024 by esther_vandeVelde — added a caveat about sampling