Molecular mass of semaglutide and why the figure differs between sources

Molecular mass of semaglutide and why the figure differs between sources — setting out what I have, and where I think it stops being reliable.

Putting the numbers in the first post, because a question about a compound without them turns into a question about somebody's impression of it.

semaglutide, monoisotopic mass near 4113.6 Da, 30 weeks of my own notes, and 9 lots from 4 suppliers with a purity figure on each. That is the whole basis of what follows.

What I want checked is the reasoning I have built on top of it, not the figures themselves.

Adding the measurement that the opening post says would settle it.

The STEP programme populations were selected: enrollment criteria required baseline body mass index over 30, no recent blood pressure crisis, no recent retinopathy, no renal disease at the time. Applying results from that population to someone well outside it is an extrapolation and should be called one.

The reasoning is more useful than the number, which is why I have shown it.

Reading back through, this was answered upthread and I missed it. My fault.

Adding the boring version of molecular mass of semaglutide, 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.

Answering the question post #4 raises rather than the one it answers.

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.

I would put the burden of proof on the interesting explanation, not the dull one.

The oral formulation is a genuinely different pharmaceutical problem from the injectable and shares only the active molecule. Absorption enhancers, fasting requirements and a very different bioavailability mean dose numbers do not translate between the two at all.

A single observation, in a thread that deserves better than single observations.

I keep a log for molecular mass of semaglutide specifically because my memory of it turned out to be systematically wrong in one direction. Six weeks of notes cost nothing and settled it.

For anyone finding this later: the short answer on molecular mass of semaglutide is that it depends on one thing, and the rest of the thread is people identifying which thing.

On alcohol: the labelling does not contraindicate it, but it raises gastric irritation risk and semaglutide already does that. There is no published interaction study and the conservative position is to limit it if you are titrating or if gastrointestinal symptoms are troublesome.

Worth reading the earlier posts in this thread before acting on mine.

Practical note on molecular mass of semaglutide: write down what you expect before you look. The number of times I have found what I went looking for is higher than chance would allow.

Renal outcomes moved this compound out of the metabolic-only conversation. FLOW reported on kidney endpoints in people with type 2 diabetes and chronic kidney disease, which is a narrower population than the discussion here usually assumes.

Adding a source would improve this post and I do not have one to hand.

I had written a reply contradicting post #10 and deleted it. Here is what survived.

The claim about molecular mass of semaglutide upthread is stronger than its source supports. I have read the source. The source says "associated with" and the post says "causes".

Acknowledging rather than arguing. The reasoning holds as far as I can follow it.

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.

That is a description of practice, not a recommendation of it.