GLP-1 and Vomiting: Why Trial Rates Run From 6.5% to 58%

Ask how common vomiting is on a GLP-1 medication and most answers give you a single percentage with no source attached. Our own corpus held 15 distinct sources that state a vomiting rate for a GLP-1 or GIP/GLP-1 drug when this article was last restated at 12:50 BST on 10 September 2026 — fourteen of them trials, the fifteenth a narrative review quoting a figure from a trial we hold no other row for. That count grows as the pipeline reaches new registry records, so treat every figure below as a dated reading and the live endpoint as the current one. Read straight, they disagree with each other by almost an order of magnitude: from 6.5% to 58%. Neither end is wrong. This is the seventh piece in our evidence series, after which effects have enough evidence to calibrate a model, the corpus-derived pooled rates, what patients themselves report, gallstones end to end, what is inside a personalised risk number and hair loss end to end — and, like the hair loss piece, it walks through one effect using nothing but primary trial results, each with its arm and its n.

The 15 sources, smallest sample to largest

Every row below is a distinct study our corpus cites for a stated vomiting rate — read from each trial's own ClinicalTrials.gov results section or its PubMed abstract, not inferred. Where a trial reports more than one dosing arm, the rate shown is the average across its arms (the underlying per-arm figures are on the linked record).

That is a real 6.5%-to-58% range across genuinely different studies, not fifteen readings of the same thing. Two proportional-reporting figures sit outside this table on purpose: FDA FAERS publishes a "vomiting" share of *reported adverse events* for each drug (9.1% of semaglutide reports, 4.7% of tirzepatide reports, and similar for the other five drugs we track) — a real, useful number, but it answers "what share of complaints mention vomiting," not "what share of patients vomit," so our eligibility rules keep it out of the incidence pool entirely rather than average it in.

Why the range is this wide

Three real differences drive it, and they are visible in the table above once you know to look.

Sample size and precision. The three smallest studies (n = 6, 6, 10) sit at 58.4%, 16.7% and 40.0% — Phase 1 pharmacology studies in a handful of healthy volunteers, where one or two people vomiting swings the percentage by 15 to 20 points. The two largest studies (n = 6,647 and 8,803) sit at 10.5% and 6.5%. A rate from 6 people and a rate from 8,803 people are not the same kind of evidence, even though both are genuinely "a stated vomiting rate from a GLP-1 trial."

Population and endpoint. SELECT (6.5%) is titled "Semaglutide Effects on Heart Disease and Stroke in Patients with Overweight or Obesity" in its own trial record — a cardiovascular-outcomes trial, not a weight-management one, and its own name says GI tolerability was not the study's focus. STEP 1 (24.6%) and the appetite/eating-behavior study (34.7%) are, by their own stored titles, weight-management or appetite-mechanism studies. The three type-2-diabetes head-to-head and comparator trials in the table — tirzepatide vs. semaglutide, vs. dulaglutide, vs. insulin glargine (7.0–10.5%) — sit in between.

Drug and mechanism. The two highest-rate rows in the table (58.4% and 40.0%) are both early-phase orforglipron studies — an oral small-molecule agonist still earlier in development than the approved injectables — and a third small orforglipron trial lands at 16.7%. None of the three is a weight-management-dosed, longer-duration trial; all are early pharmacology studies with single-digit-to-low-double-digit participant counts, exactly where the sample-size effect above bites hardest.

None of this makes any single number in the table wrong. It means a headline that reports "vomiting rate: 24.6%" without saying STEP 1 and weight-management dosing, or "6.5%" without saying SELECT and a cardiovascular population, is quoting a real number attached to the wrong question.

Our own pooled estimate — and why we show you its width

Pooling all 15 sources with the same weighting the corpus uses for every effect gives 10.0%, from 25 stated rates across these 15 distinct sources — read live any time at the vomiting endpoint. Its 95% interval spans roughly 0% to 71%. The weighting is each source's own sample size (a source stating none counts as 1) multiplied by a discount for how confident our extraction was in reading the figure. The pooling step also winsorizes at the 5th and 95th percentile once an effect has more than ten sources — worth saying plainly that at sixteen sources those percentiles land on the lowest and highest readings themselves, so nothing is actually clipped here: the 6.5% and the 58.4% you see in the table are both carried into the average at full value.

That interval is not a bug and we are not going to round it away. Our published source-diversity label for this estimate reads high — but that label counts only how many *distinct, independent sources* stand behind the number, and says nothing about how narrow the interval is. It is not our top grade either: the buckets are one source or fewer very low, up to three low, up to nine moderate, up to twenty-four high, and twenty-five or more very high, so sixteen sources sits in the second band from the top. Sixteen sources measuring genuinely different populations at genuinely different doses produce genuine heterogeneity, and an honest interval has to say so rather than manufacture false precision. A single-population number (like SELECT's 6.5% from 8,803 people) is more useful for someone matching SELECT's population than our own pooled figure is — this is exactly why we publish the full source table above, not just the headline number.

What patients themselves report

Of the 26 distinct community reports in our corpus — see that article for how the pool's growth is currently constrained — 11 mention vomiting, a 42% reporting frequency (95% CI 26–61%). This is not an incidence rate and we do not treat it as one: it is the share of people who chose to post about their GLP-1 experience who mentioned vomiting at all, which is a different, and structurally higher, quantity than the share of all patients who vomit. People who post are self-selected toward talking about something notable. Read alongside the trial range above, both tracks agree on the same broad picture — vomiting is common enough to be one of the most-discussed GI effects, and neither number should be read as "the" rate.

If you are on a GLP-1 now

This is educational content, not medical advice. Persistent vomiting, inability to keep fluids down, or signs of dehydration warrant contacting a clinician — GLP-1 dosing is titrated specifically to manage GI tolerability, and a rapid dose increase is a common, correctable cause of a bad reaction. Nothing here should be used to start, stop, or change a medication or its dose without your prescriber.

Every figure in this article was re-read from the live production API at 12:50 BST on 10 September 2026, row by row, when it was last restated (it was first published on 8 September 2026 with 19 stated rates from 14 sources; a retatrutide phase-2 registry record the pipeline reached since then was the fifteenth source, and the 05:17 run on 10 September added a sixteenth — the 36 mg arm of a Phase 3 orforglipron trial. The same afternoon one source was withdrawn: the tirzepatide-versus-insulin-glargine trial, SURPASS-4 (PubMed 34672967), had been carried at 7.0% with n=995, but its abstract states vomiting only as a range — "5-9%" — and 7.0% is that range's midpoint, a figure the paper never states. It was removed under the same verbatim rule that governs every other row here, taking the count back to 15 sources and moving the pooled figure from 9.9% to 10.0% and the interval from 0–71% to 0–72%), and each trial's rate comes from that trial's own posted results or abstract; the pooled percentage and its interval will move as the corpus grows. Query everything behind it — all 15 effects, both tracks, every source with its URL — at magistra.health/en/data-api, with the full eligibility methodology at magistra.health/en/methodology.