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What does STEP 1 actually establish about semaglutide?

Asked 25 Feb 2025Modified 14 months agoViewed 14k times
17

The case in front of me: STEP 1 · semaglutide.

The figures are clear enough; the question is what they mean and what they do not.

I can supply the numbers if the specifics change the answer.

What can I legitimately conclude from this figure?

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SS
askedswirl_dont_shake10k1425 Feb 2025
Worth saying whether you want relative or absolute risk. They read very differently. – nine_point_nine 7 months ago
8Same question, and the two papers I found disagree, which is why I am watching. – linnea_wahlberg 5 months ago
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5 Answers

Accepted answer first, then by votes
34

Accepted answer

Whatever its primary endpoint was, at the power it was designed for, in the population it recruited — and nothing else. STEP 1 was sized to answer one question. Every other result in it is a secondary or exploratory endpoint, powered incidentally if at all, and a nominally significant secondary in a programme with twenty of them is what you would expect from chance alone. So the reading order is: primary endpoint, then whether the secondaries were pre-specified and hierarchically tested, then everything else as hypothesis-generating. A trial establishes one thing well and suggests several things badly, and the press coverage inverts that ranking reliably.

In practice, the trial answers a narrower question than the headline suggests, and the narrowing is where the useful information is.

Placebo arms in this class are not nothing. Lifestyle-intervention placebo arms in the major obesity trials commonly lose two to three per cent of body weight, so an active-arm figure quoted without its comparator overstates the drug effect by roughly that much.

Duration decides what can be seen. A 68-week trial can measure weight and glycaemia; it cannot measure anything whose event rate is one per cent per year without enrolling tens of thousands.

Where a result is quoted from a conference abstract rather than a peer-reviewed publication, the numbers routinely move between the two. It is worth checking which one you are reading.

The short version: check the endpoint, check the comparator, check who was excluded, then look at the number.

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DV
answered · acceptedDr_Ilse_Vandenberg113k2485 Mar 2025
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40

Answer first: read the primary endpoint, the comparator and the population before you read the effect size. Almost every argument on this site about a trial is really an argument about one of those three.

A composite endpoint is only as informative as its least serious component. Where a cardiovascular composite combines death, infarction and stroke, ask which component moved, because they are not interchangeable outcomes.

Open-label extensions are not the same evidence as the randomised phase. Once everyone knows what they are taking, the reported outcomes acquire a bias that no analysis fully removes.

Meta-analyses in this area are dominated by whichever trial contributed the most participants, so read the forest plot rather than the summary estimate.

I am not a clinician and this is not medical advice; it is a reading of a published protocol.

Read the protocol and the statistical analysis plan if the result matters to you. Both are usually published alongside.

edited 9 Apr 2025 by Dr_Colm_Fitzhenry — fixed an arithmetic slip in the third paragraph

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DF
answeredDr_Colm_Fitzhenry69k24728 Mar 2025
8Thank you — this is the answer I was looking for. – meniscus_film 4 months ago
This matches what I was told by a clinician, for whatever that is worth. – coldpack_88 6 months ago
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26

The honest answer here is that the published evidence supports part of the claim and is silent on the rest, and it is worth being precise about which part is which.

Confidence intervals matter more than point estimates when two trials disagree. Two studies reporting fifteen and twenty per cent whose intervals overlap heavily have not disagreed about anything.

Non-inferiority and superiority designs are not interchangeable. A non-inferiority result says the new agent is not meaningfully worse against a pre-specified margin — it does not say it is as good, and it certainly does not say it is better.

Be careful about generalising from a trial population to yourself. The exclusion criteria are usually the most informative page in the supplement.

Quote the interval alongside the estimate and half the disagreements on this site would not start.

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DV
answeredDr_Bram_Verhoeven84k2488 Apr 2025
16

The short version: the effect is real, the magnitude depends on the population, and the population is usually the part that gets dropped when a result is quoted second-hand.

Trial populations are selected. Exclusion criteria in this class routinely remove people with significant renal impairment, prior pancreatitis and unstable psychiatric illness, which is exactly the population the results are then quoted for.

The cardiovascular outcome programme in this class runs to several large randomised trials — LEADER for liraglutide, SUSTAIN-6 and SELECT for semaglutide, REWIND for dulaglutide — and they are the reason the class is discussed as more than a weight intervention.

One qualification: absence of a signal in a trial of this size is not evidence of absence for a rare event. It is evidence that the event is rarer than the trial could detect.

If a claim cannot be traced to a named trial with a named endpoint, treat it as a claim rather than as evidence.

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NO
answerednkem_obiora39k3811 Jun 2025
15

Look at the discontinuation rate alongside the efficacy figure. A large effect in the two thirds who stayed is a different result from a large effect in everyone.

Intention-to-treat and per-protocol analyses answer different questions. ITT asks what happens if you offer the treatment; per-protocol asks what happens if it is taken as directed. The gap between the two is a measure of how tolerable the protocol was.

When two sources disagree, the answer is almost always in the methods section of the one you have not read.

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MO
answeredmarta_okonkwo190k25817 Mar 2025
Which population was that figure from? It moves a lot between the trials. – coldbox9 5 months ago
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Your answer

Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.

Not medical advice. Research-use-only compounds are not approved for human use.