# Semaglutide at 68 and 104 weeks

> Longer treatment | Boston Weight Loss Clinics — Semaglutide at 68 and 104 weeks, and why duration matters: a follow-up essay from Boston Weight Loss Clinics.

**Continued treatment**

The early weight result is impressive. The longer trial earns attention by staying with the question.

## The STEP 1 result

At first, I was preoccupied by the size of the reduction. The more useful question turned out to be how long the observation lasted, and under what conditions. That adjustment begins with giving the initial finding its full strength.

[STEP 1 enrolled 1,961 adults with overweight or obesity without diabetes](https://pubmed.ncbi.nlm.nih.gov/33567185/). The trial studied subcutaneous semaglutide, meaning an injection under the skin. At 68 weeks, mean body-weight change was −14.9% with semaglutide and −2.4% with placebo. Those results came from the trial's once-weekly 2.4 mg regimen.

I respect the size of that result on its own terms. There is no need to make it more dramatic by turning a group mean into the experience of a particular person. The comparison already carries an argument: the semaglutide group had a much larger mean reduction than the placebo group over the period measured.

Still, an endpoint has an ending built into it. The trial's result answers the question at 68 weeks. The later trial adds confidence by examining whether a meaningful reduction remains over a longer period of treatment.

## The STEP 5 follow-up

[STEP 5 reported sustained, clinically meaningful mean weight loss over 104 weeks](https://pubmed.ncbi.nlm.nih.gov/36216945/). Adults with overweight or obesity received semaglutide or placebo; the semaglutide regimen studied was 2.4 mg once weekly by subcutaneous injection. Mean weight reduction remained significantly greater than with placebo.

This quieter paper deserves a place beside the celebrated initial result. Continuing to observe an effect makes a difference to the argument. It gives duration some substance, beyond the hope that the earlier endpoint will simply hold.

On this question, I favour the longer observation over another contest for the most eye-catching weight-loss number. That preference rests on the sustained result STEP 5 reported. The paper concerns continued treatment. A conclusion about persistence under that condition leaves the withdrawal question open.

I value the ordinary persistence of this question. An initial change can dominate an account because it is so easy to state. Asking about a later result gives the duration of treatment some of the attention already paid to the magnitude of the change.

There is also a difference between finding the result exciting and finding the sequel satisfying. The first result supplies the reason to look further. The longer result adds something the initial observation could only leave open: evidence of a sustained reduction during the longer period studied.

![Two illustrated technicians checking a freestanding weighing instrument beside an arched window](images/repeat-measurement.webp)

*An imagined measurement room, drawn for this essay; it depicts no named laboratory or trial event.*

## Body composition in SURMOUNT-1

The scale total has components, too. Here the research moves to tirzepatide: a [post hoc SURMOUNT-1 body-composition substudy found that about 75% of the weight lost was fat mass and about 25% was lean mass](https://pubmed.ncbi.nlm.nih.gov/39996356/). These proportions occurred in both tirzepatide and placebo groups and were consistent across most subgroup analyses.

[The substudy included 160 people, with 124 in the pooled tirzepatide group and 36 receiving placebo](https://pubmed.ncbi.nlm.nih.gov/39996356/). It used DXA, an imaging method for assessing body composition. The later measurement at 72 weeks examined what had changed within the total weight.

I welcome the complication this introduces. A falling total can contain changes in both fat and lean tissue. The comparison also resists treating the observed proportion as peculiar to tirzepatide, since both groups had a similar split in the weight lost. That makes the finding more interesting than a simple celebration of fat loss or alarm about lean mass alone.

Duration and composition add different things to the original weight result. The consequences of these composition changes are the follow-up question I hope later work will answer. For now, the explicit breakdown gives the follow-up another worthwhile question. The next turn is [tirzepatide after withdrawal](/stopping).

That seems a much richer account of progress than the total on its own. It also makes the next observation worth waiting for.

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I follow the later chapters of published research at Boston Weight Loss Clinics, an editorial site rather than a clinical business, and nothing here supplies medical advice.