Fine by me. I had wanted a stronger conclusion and there is not one available.
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Compounds · Semaglutide · continued
Semaglutide half-life: where the 165 to 184 hour figure comes from posts 91–120
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Post #90 put the caveat in the right place and I want to underline it.
The mass figure differs between sources because of how the different entities report it. The monoisotopic mass of the bare peptide is one number; the mass including the acylation is another. Different sources emphasise different details.
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Leiterman, post #45: I had written a reply contradicting post #41 and deleted it. Here is what survived. The 165 to 184 hour half-life range gets quoted as a fixed number. It is a range across a studied population, and individual clearance varies enough that a person's own steady state may be reached earlier or later than the population average implies. Go to post
Appetite effects and gastrointestinal effects are frequently reported together and are not the same mechanism reported twice. Slowed gastric emptying contributes to both, but central satiety signalling accounts for effects that persist after emptying has normalised.
It took me longer than it should have to see that.
Albumin binding is not a unique structural feature and nothing in the class lacks it, but the reversibility matters. Semaglutide binds albumin covalently through a fatty side chain, which creates a very long half-life at the cost of sequestering the free form. That is a trade-off and it is the trade-off that allows weekly dosing.
The interesting part of this is the exception, and I do not understand the exception.
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Post #92 is the version of this I will quote in future. One addition.
Two claims get bundled together under semaglutide half-life and they need separating. The descriptive one — this is what was observed — is usually well supported. The causal one — this is why — usually is not.
Almost every disagreement in threads like this one dissolves once you say which of the two you are making.
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Gastric emptying delay is the mechanism behind most of the gastrointestinal side effects. Slowing the stomach empties it feeds less food into the intestines at a time, which is part of the satiety mechanism but is also why nausea is dose-dependent and titration-dependent.
Written in the hope of being told what I have missed.
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r.venkatesan, post #57: Injection site does not appear to matter much for semaglutide exposure. The published comparisons of abdomen, thigh and upper arm found differences small enough to be clinically unimportant, which is not true of every injectable. I would be interested in a counterexample if anyone has one. Go to post
Discontinuation rates in the trials are worth reading alongside efficacy and almost never are. A large mean effect in a population where a meaningful fraction stopped early is telling you two things, not one.
I am reporting what happened, not recommending it.
Semaglutide versus liraglutide in STEP 8: semaglutide produced greater weight reduction and the discontinuation rates differed. But the trial was open-label for the dosing schedule, which admits expectation effects. Weekly versus daily itself is part of the comparison, not a confounding variable to be removed.
Someone should write this up properly, and it should probably not be me.
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Adding the boring version of semaglutide half-life, because the interesting version keeps getting posted and the boring one is usually right.
Check the ordinary explanations, in order, and stop when one of them accounts for what you are seeing. Most of the time the second one does.
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p.mwangi, post #31: Confirming post #30 from a second method, which matters more than confirming it from a second person. The mass figure differs between sources because of how the different entities report it. The monoisotopic mass of the bare peptide is one number; the mass including the acylation is another. Different sources emphasise different details. Go to post
Second this, and I would have said it less carefully.
The C-cell question: semaglutide triggered medullary thyroid carcinoma in rodent toxicology studies. A signal in rodents does not automatically appear in humans, but it is the reason the compound is contraindicated in people with personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2.
Adding this to the thread rather than to the wiki, because I am not confident enough for the wiki.
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Coming back to post #101, because the follow-up matters more than the original answer.
On the injection-day question: the labelling for licensed semaglutide allows the day to be changed provided at least two days separate the two injections. That interval is not arbitrary — it is what stops two doses stacking inside one absorption window.
The general answer and the answer for your case may diverge here.
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ambient_review, post #43: On post #41 — agreed on the reasoning, with one qualification. On the injection-day question: the labelling for licensed semaglutide allows the day to be changed provided at least two days separate the two injections. That interval is not arbitrary — it is what stops two doses stacking inside one absorption window. I would hold that… Go to post
Discontinuation rates in the trials are worth reading alongside efficacy and almost never are. A large mean effect in a population where a meaningful fraction stopped early is telling you two things, not one.
Solutions of semaglutide can look faintly opalescent without anything being wrong. Visible particulate, fibres or frank cloudiness are a different observation entirely and are worth raising with the supplier rather than reasoning about.
That is the version I would defend. It is not the version I started with.
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I read post #104 twice before replying, because I had assumed the opposite.
On identity confirmation: a mass close to 4113.6 Da on the intact molecule is consistent with semaglutide and is also consistent with several closely related species. Mass narrows the field; it does not close it, and no certificate should be read as though it did.
I have separated what I observed from what I concluded, which does not always happen.
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bench_peak, post #95: Post #92 is the version of this I will quote in future. One addition. Two claims get bundled together under semaglutide half-life and they need separating. The descriptive one — this is what was observed — is usually well supported. The causal one — this is why — usually is not. Almost every disagreement in threads like this one… Go to post
Agreed on all of that, and I have nothing to add to it.
e.silva, post #11: Right, and stated more narrowly than I would have dared to state it. Go to post
Post #108 and I disagree about the size of the effect, not about the direction.
Injection site does not appear to matter much for semaglutide exposure. The published comparisons of abdomen, thigh and upper arm found differences small enough to be clinically unimportant, which is not true of every injectable.
This is the version I would want a new member to read first.
s.zamora, post #105: I would call the community position on semaglutide half-life likely rather than established, and I would be comfortable defending that hedge. Go to post
I changed my mind about semaglutide half-life after someone here asked me for the source and I could not produce one. That is worth saying out loud because it is the ordinary way it happens.
Picking up post #111: that is the part I would want checked first.
What would change my mind on semaglutide half-life is a second dataset collected by someone with no stake in the first. Until then I hold it loosely and I would rather say so than pretend to more.
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The opalescent appearance in semaglutide solutions is occasionally noted and the mechanism is unclear. It does not appear to correlate with product failure in practice. Visible particles or frank cloudiness is different and would be reason to contact the supplier.
Someone will know this better than I do and I hope they say so.
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Collapsed as off-topic by two members at trust level 3 or above
Reading back through, this was answered upthread and I missed it. My fault.
a.cabrera, post #7: Where I part company with post #4, and it is a narrow parting. Semaglutide half-life looks different depending on whether you are reading the primary literature or the summaries of it, and the difference is not in our favour. Go to post
Worth separating two things that post #111 runs together.
Research-use-only semaglutide is not a licensed medicine, is not manufactured to pharmaceutical standards, and is not approved for human use. That is a statement about what it is, not a coded opinion about anything.
The short answer was in the first line; everything after is the working.
This follows post #115 rather than contradicting it.
I think the semaglutide half-life question is answerable and has not been answered, which is a more optimistic position than most of this thread.
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Semaglutide half-life has been discussed here with more heat than it deserves, mostly because two definitions have been in play the whole time.
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n.serrano, post #46: Nothing to add on the substance. Thank you for taking the question at face value. Go to post
Albumin binding is not a unique structural feature and nothing in the class lacks it, but the reversibility matters. Semaglutide binds albumin covalently through a fatty side chain, which creates a very long half-life at the cost of sequestering the free form. That is a trade-off and it is the trade-off that allows weekly dosing.
The 165 to 184 hour range: that is roughly 7 to 7.6 days, which is why the weekly schedule works. Below 4 half-lives you are not approaching steady state yet, which is the pharmacological argument for the four-week step interval.
Scoping that to what I have actually seen rather than what I have read.
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