Does Semaglutide or Tirzepatide Cause Hair Loss? What the Trial Registries and the Label Actually Report
The US semaglutide label puts hair loss at 3% versus 1% on placebo, and says it was associated with weight reduction and reported several times more often in women than in men. The tirzepatide registry posts alopecia per arm at about 5% versus 1.1%, and as of 7 September 2026 those three arms are also our own database's first eligible clinical rates for the effect — here is every number, the arm and n it belongs to.
Ask "does Ozempic cause hair loss?" and the answer that comes back is usually a percentage with no source attached. This piece is built the other way round: every figure below is quoted from a primary source — the current US prescribing information, or a trial's own results table on ClinicalTrials.gov — with the arm and the number of participants it belongs to. It is the sixth 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 and what is inside a personalised risk number.
The short version: hair loss is listed on the semaglutide label as one of its most common adverse reactions, at a low absolute rate that is roughly three times placebo; a 2,539-participant tirzepatide weight-management trial posts a similar-sized excess; both sources describe the event, neither settles what causes it; and, as of 7 September 2026, our own database holds its first eligible clinical rate for this effect — the tirzepatide trial's own three arms, described below, after a week at zero from zero sources (and, before 31 August 2026, a base that rested only on three seed rows we later excluded) for a reason worth explaining.
What the semaglutide label says
The current US prescribing information for Wegovy (semaglutide 2.4 mg, for weight management), revised June 2026, lists hair loss among the "most common adverse reactions (incidence ≥5%)" in its highlights, alongside nausea, diarrhoea, vomiting and constipation. Its adverse-reactions tables give the numbers:
| Trial population (label table) | Placebo | Semaglutide 2.4 mg | Semaglutide 7.2 mg |
|---|---|---|---|
| Adults with obesity or overweight, pooled placebo-controlled trials (Table 3) | 1% (N=1,261) | 3% (N=2,116) | — |
| Adults with obesity, 7.2 mg trial (Table 4) | 1% (N=303) | 3% (N=304) | 6% (N=1,311) |
| Adolescents aged 12 and older with obesity (Table 5) | 0% (N=67) | 4% (N=133) | — |
The label's narrative section adds the detail that no table shows. Quoted in full: "Hair loss adverse reactions in WEGOVY injection-treated patients were associated with weight reduction. In a pool of studies 2, 3, and 4, hair loss was reported in 3.3% of patients treated with WEGOVY 2.4 mg (4% female, 0.9% male) and in 1% of patients treated with placebo (2% female, 0 male)." And for the higher dose: "hair loss was reported in 5.8% of patients treated with WEGOVY 7.2 mg (8.4% female, 0.2% male), 3.3% of patients treated with WEGOVY 2.4 mg (5.4% female, 0 male), and 1.0% of patients on placebo (1.5% female, 0 male)."
Two things in that passage matter more than the headline 3%. First, the sex split is large: on 2.4 mg, roughly four in a hundred women against fewer than one in a hundred men. Second, the label's own framing is "associated with weight reduction" — it records the event and ties it to the weight lost, and says nothing further about mechanism. (Quoted from the prescribing information via DailyMed, accessed 6 September 2026.)
What the tirzepatide trial registry says
Tirzepatide's US label is a separate document we have not quoted here; the cleanest per-arm source for tirzepatide is the trial registry itself. The results section of SURMOUNT-1 (NCT04184622) — the trial of once-weekly tirzepatide in participants without type 2 diabetes who have obesity or are overweight with weight-related comorbidities — posts alopecia under "skin and subcutaneous tissue disorders" in its non-serious adverse-event table, by arm:
| SURMOUNT-1 arm | Participants with alopecia | At risk | Share |
|---|---|---|---|
| Placebo | 7 | 643 | 1.1% |
| Tirzepatide 5 mg | 33 | 630 | 5.2% |
| Tirzepatide 10 mg | 32 | 636 | 5.0% |
| Tirzepatide 15 mg | 37 | 630 | 5.9% |
(Read from the ClinicalTrials.gov API v2 adverse-events module on 6 September 2026; the shares are our division of the two posted counts.)
Do not read the two tables as a head-to-head. A 5% figure from one trial and a 3.3% figure from a pool of others are different populations, different durations and different reporting conventions — the registry's term "alopecia" and the label's grouped "hair loss" are not guaranteed to be the same coding. The only fair statement is that in both programmes the event ran a few percentage points above placebo, from a placebo baseline near 1%.
Where semaglutide's own registry entries fall silent. The registry records for SELECT (NCT03574597), STEP 1 (NCT03548935) and STEP 2 (NCT03552757) contain no hair-loss or alopecia term at all, because each posts its non-serious adverse events at a 5% reporting threshold and hair loss sits below it. That is why the label's pooled table, not any single semaglutide trial record, is the per-arm source for semaglutide — and why, until we corrected it on 4 September 2026, our own methodology preprint wrongly credited SELECT with a 3% hair-loss rate SELECT never reported (item 8 of its corrections log, v5.5).
What our own evidence base holds (as of 7 September 2026)
Our database holds 39 hair-loss-tagged data points — 14 clinical, 14 user-report and 11 news points — and the eligible clinical rate base for the effect was, until 13 September 2026 (see the update below), 3 stated rates from 1 distinct source: the three tirzepatide arms of SURMOUNT-1's posted adverse-event table (5.2%, 5.0% and 5.9% on 5, 10 and 15 mg; n=630, 636 and 630), stored on 7 September 2026. The hair-loss endpoint pools them to 5.4% (95% CI 4–7%) and labels the source diversity "very low" — one trial. That interval is narrow for a reason that is the opposite of reassuring: with a single contributing source the between-study heterogeneity term is 0 by construction, so 4–7% describes SURMOUNT-1's own sampling and says nothing about whether a second trial would land anywhere near 5.4%. The endpoint has said so explicitly since 11 September 2026 (`intervalBasis: "sampling_only_single_source"`). The exclusions are itemised beside it: 8 clinical points that discuss the effect without stating a comparable numeric rate, and 3 April-2026 seed rows excluded on 31 August 2026 because they restated our own static table under a trial URL no extraction ever read. From 31 August to 7 September 2026 the base was 0 from 0 and the endpoint served a labelled published-literature fallback (the label's 3% from 4 September; before that, a 1–3% range with no recorded derivation, corrected the same day); until 31 August the base had counted the three seed rows.
Update, 14 September 2026 (21:56 BST). The paragraph above describes the 7 September corpus. In the morning run of 14 September 2026 the registry re-collection reached a second source: NCT05548647 (semaglutide; a mechanistic study of appetite and eating behaviour) posts alopecia in two arms — 7 of 72 participants (9.7%) and 0 of 10 — which our per-source list shows as the arm average, 4.9%, beside the larger arm's n. The hair-loss endpoint published, until 15 September 2026, 5 stated rates from 2 distinct studies, pooled 5.3% (95% CI 4–7%), source diversity "low" rather than "very low", and its interval carried a between-study term again (`intervalBasis` reads `sampling_plus_between_study`, no longer `sampling_only_single_source`). Update, 15 September 2026 (10:39 BST). The 15 September run stored a third source: NCT05971940, an orforglipron trial, posts alopecia in three arms — 0 of 143 (0%), 1 of 137 (0.7%) and 2 of 141 (1.4%), shown in our per-source list as the arm average, 0.7%, beside the largest arm's n — so from 15 September 2026 until the 23 September run the endpoint published 8 stated rates from 3 distinct studies, pooled 4.5% (95% CI 2–12%), still "low"; the interval widened because the new source sits well below the first two. Update, 24 September 2026. The 23 September run stored the alopecia rows of both arms of SURMOUNT-5 (NCT05822830, tirzepatide vs semaglutide), so the 15 September counts are no longer current; the live endpoint carries today's figures. The corpus holds 47 hair-loss-tagged points (20 clinical, 14 user-report, 13 news). So "one trial" in the question and bullets below, and "the base above is tirzepatide-only", describe the 7 September state: SELECT, STEP 1 and STEP 2 still post no alopecia term, so the label remains the only per-arm semaglutide 2.4 mg source, and the second study is a small semaglutide mechanistic trial, not a pivotal one.
Why one trial, when the two tables above exist? Two mechanisms, both verifiable:
On the community track, 1 of 42 distinct community reports (2.4%) mentions hair loss (Restated 25 September 2026 from 1 of 26 (3.8%) when ten GLP-1 communities were admitted to the report pool, taking it from 26 to 42.) — a reporting frequency, not an incidence rate, from a pool that cannot currently grow. It is worth remembering that before 14 August 2026 this same effect carried a "39%" real-world figure on our site, produced by averaging what individual posts claimed — one X/Twitter post claiming "76%" did most of the work. That number was withdrawn, the method replaced, and the correction published; the honest community figure for hair loss today is one report in forty-two.
Is it the drug or the weight loss?
The sources do not say, and we are not going to say for them. The semaglutide label's wording is "associated with weight reduction"; the SURMOUNT-1 registry posts counts and attributes nothing. What the two sources do agree on is the shape: an event reported by a few percent of participants, a few points above placebo — and the label adds that, for semaglutide, it is concentrated in women.
A correction of our own belongs here. Until today, the hair-loss description served by our API and predictor read "likely caused by nutritional deficiency from rapid weight loss and reduced caloric intake, not a direct drug effect" — a plausible hypothesis typed in April 2026 that no primary source we hold (the label, the registries) states. It now carries the label's own wording and nothing beyond it. We publish the correction rather than quietly editing because a confident mechanism claim with no citation is precisely the kind of sentence this series exists to remove.
What the 2026 meta-analyses add (section added 7 September 2026)
Two pooled analyses published this year answer the question the label and the registry leave open — how much more often hair loss is reported on a GLP-1 than on placebo — and one of them states an absolute rate. Both were read from their PubMed abstracts on 7 September 2026; the figures below are quoted, not derived.
Two things to keep in view when using these numbers. A risk ratio of 3.3 from interventional studies and an odds ratio of 1.4 from three cohort studies are not in conflict: they pool different study designs over different denominators, and a ratio says nothing about the absolute rate until it is anchored to one — which is why the 3.9% event rate and the label's 3% are the figures to quote to a patient, and the ratios are the figures that answer "more than placebo?". And a third 2026 review (Gupta et al., Science Progress, PMID 41998799, 24 studies) reports no pooled estimate but describes the same pattern qualitatively: semaglutide and tirzepatide carry the highest reported incidence, hair loss with semaglutide "appeared to be dose-dependent" with doses under 2 mg weekly "rarely implicated", and females "appeared to be disproportionately affected" — consistent with the label's sex split above.
We have not typed any of these figures into our own database: its eligible base is built from per-study stated rates with their n, and a ratio pooled across studies is a different kind of number. They are cited here so that anyone quoting "does it cause hair loss?" has the strongest available answer beside the primary tables, with the paper it came from.
If you are on a GLP-1 now
This is educational content, not medical advice. Hair loss is listed on the semaglutide label as a common adverse reaction; the same label, in its patient section, tells readers to talk to their healthcare provider about any side effect that bothers them or does not go away. Nothing here should be used to start, stop or change a medication — that is a conversation with a clinician who knows your history.
Every figure in this article was read from the cited primary source or from our live production API on 6 September 2026 (the meta-analysis section: from PubMed abstracts on 7 September 2026; the evidence-base update: from the live API on 14 September 2026) and is stated as of that date. 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.
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