What is the reported incidence of constipation on tirzepatide in SUSTAIN-6?

Concretely: constipation · tirzepatide · SUSTAIN-6.

I would like to know the limits of what can be inferred from this.

What I am trying to avoid is over-reading a single result, which I have done before.

What would I need in addition before this supported a decision?

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.

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.

Injection-site reactions are more often diluent-related than peptide-related. Benzyl alcohol sensitivity is uncommon but real, and it presents as a consistent local reaction at every site with a preserved diluent and no reaction with an unpreserved one — which is a straightforward thing to establish. Injection depth is the other common cause: intradermal placement stings and welts, subcutaneous placement usually does not.

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.

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.

Nausea incidence in the pivotal trials runs to roughly 40 to 45 per cent at the higher doses against 15 to 20 per cent on placebo, with vomiting at roughly 15 to 25 per cent against 5 to 8 per cent. Discontinuation specifically attributable to gastrointestinal adverse events was in the range of 4 to 7 per cent. Those are the numbers to hold in mind when someone describes their experience as unusual.

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.

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

edited 29 Jun 2025 by lipid_panel_q — added the placebo-arm figures

Look at the placebo arm before concluding anything about attribution. The placebo-arm rates for most of these events are not small, because the events themselves are common in the underlying population.

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.

Telogen effluvium following substantial weight loss is documented independently of any pharmacotherapy, which is the cleanest argument that the rate of loss rather than the agent is the primary driver.

One qualification — reported incidence in a monitored trial population is a lower bound on what happens in an unmonitored one, because trial participants were escalated to protocol and supported through it.

If the timing does not fit the escalation, look for another explanation before settling on the drug.

More usefully, the distinction worth making early is between a tolerability problem, which is unpleasant and self-limiting, and a clinical problem, which is neither. They present differently and the thresholds for each are worth writing down before you need them.

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.

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].

Worth being explicit: nothing here is medical advice, and research-use-only compounds are not approved for human use.

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

edited 31 Mar 2025 by Dr_Colm_Fitzhenry — added the method parameters