Does Semaglutide or Tirzepatide Cause Hair Loss? What the Trial Registries and the Label Actually Report

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 our own database currently holds no eligible clinical rate at all for this effect, 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:

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:

(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 6 September 2026)

Our database holds 36 hair-loss-tagged data points — 11 clinical, 14 user-report and 11 news points — and the eligible clinical rate base for the effect is 0 stated rates from 0 distinct sources. The hair-loss endpoint therefore serves the label's 3% as a labelled published-literature fallback rather than a corpus-derived estimate, with the exclusions 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.

Why zero, when the two tables above exist? Two mechanisms, both verifiable:

Abstracts describe hair loss; results tables count it. Our PubMed collector reads abstracts, and the pivotal trials' abstracts mention hair loss qualitatively if at all — the per-arm percentages live in the labels and the registry tables, which is exactly where we had to go for this article.

Our registry collector has not reached SURMOUNT-1. It stores posted adverse-event tables per arm, and has stored 73 per-arm adverse-event rows from 26 trials so far, but each of its queries reads the ten most recently updated studies, and SURMOUNT-1 is not among the 26. The figure exists, in a form our pipeline can read; the rotation simply has not surfaced it. If and when it does, the endpoint above is where the change would show.

On the community track, 1 of 26 distinct community reports (3.8%) mentions hair loss — 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 twenty-six.

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 source we hold actually 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.

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 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.