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How comparable are tirzepatide and liraglutide on the evidence available?

Asked 16 Feb 2025Modified 17 months agoViewed 16k times
6

What I am working with: tirzepatide · liraglutide.

I am trying to choose between two options that are usually discussed as though only one exists.

I am not optimising for price, but I am not indifferent to it either.

Which axes does this decision turn on?

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TM
askedtwo_two_micron9.3k1616 Feb 2025
5Do you have the population it was measured in? The figure moves a lot between them. – e_dziedzic 2 months ago
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3 Answers

Accepted answer first, then by votes
87

Accepted answer

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.

The relevant detail is that 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.

Registry entries at ClinicalTrials.gov carry the pre-specified primary endpoint with a timestamp, which is the cheapest available check on whether an endpoint was changed after the data were seen.

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

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CR
answered · acceptedcoring_risk27k2715 Mar 2025
4The number needed to treat is the framing that finally made this concrete for me. – plate_count_9k 2 months ago
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35

Before comparing two trials, check whether they share an endpoint definition. Frequently they do not, and the numbers then are not comparable in any sense.

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.

Put another way, 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.

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

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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DK
answeredDr_Tomas_Kral53k383 Mar 2025
5Which population was that figure from? It moves a lot between the trials. – j_wierzbicki 9 months ago
4Adding a vote because this deserves more of them. – Dr_Sara_Kuusela 7 months ago
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24

Start with what the trial was powered for. Everything else in the publication is secondary, exploratory, or a subgroup, and those three words mean three different things.

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.

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.

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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answeredDr_Rosalind_Achebe69k14720 Feb 2025
2This matches what I was told by a clinician, for whatever that is worth. – nkem_obiora 2 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.