The question
Semaglutide produced greater average weight loss than liraglutide in STEP 8. The useful question is what that comparison included: particular injectable regimens, a defined population and a shared observation period. A result for those conditions is more informative than a blanket claim that one ingredient is universally better.
In the randomized study, 338 adults with overweight or obesity, without diabetes, entered active-treatment or placebo groups. At 68 weeks, estimated mean weight change was −15.8% with semaglutide and −6.4% with liraglutide. The between-group difference was −9.4 percentage points, with a 95% confidence interval from −12.0 to −6.8. Novo Nordisk funded the trial and participated in its design and analysis. Original STEP 8 report.
What “9.4 percentage points” tells you
Subtracting 6.4 from 15.8 gives 9.4. That is a difference between two percentages, so its unit is percentage points. Calling it “9.4% more weight loss” introduces a different calculation without telling the reader which denominator was used.
Consider an explicitly hypothetical starting weight of 100 kilograms. A 15.8% reduction would equal 15.8 kilograms; a 6.4% reduction would equal 6.4 kilograms. The difference would be 9.4 kilograms in this example. At another starting weight, the kilogram amounts change. This arithmetic illustrates the units; it is not a participant story or a personal forecast.
There is another distinction hiding in the word “average.” A mean compares groups, while an individual response belongs to a distribution. Two people can fall on opposite sides of the group averages without contradicting the trial. The headline tells us about the comparison, not exactly what will happen to a particular reader.
Read the trial as a treatment comparison
STEP 8 used weekly subcutaneous semaglutide and daily subcutaneous liraglutide, with lifestyle intervention. The active comparison was open-label. Its primary analysis evaluated treatment assignment regardless of treatment discontinuation or rescue intervention. These design features matter when interpreting the reported difference. Study methods.
An assignment-based analysis and an analysis restricted to continued treatment ask different questions. The former is closer to “what happened after people were assigned this strategy?” The latter narrows attention to treatment exposure. Neither label should disappear when numbers are copied into a comparison table.
For a reader checking a claim, a practical exercise is to underline the intervention and circle the outcome. “Semaglutide versus liraglutide” identifies the comparison only partially. The formulation, route, study population and time point complete the sentence. If a webpage swaps in a tablet, another formulation or a different population, it needs evidence for that additional claim.
More weight loss is not a complete safety comparison
Adverse events led to treatment discontinuation in 3.2% of the semaglutide group and 12.6% of the liraglutide group. Gastrointestinal events were common. These trial observations do not prove that either option is suitable for every person. STEP 8 safety results.
It is tempting to put efficacy and tolerability into a single winner-and-loser ranking. That shortcut hides the decision a clinician and patient actually face. Prior medical history, contraindications and the specific medicine's current labeling still matter. A trial average cannot resolve those questions on its own.
Saxenda's prescribing information, for example, includes contraindications and a boxed warning about thyroid C-cell tumors observed in rodents, with uncertain human relevance. A comparison of average weight change does not cancel those warnings. Saxenda prescribing information.
Match evidence to the actual medicine
FDA identifies Saxenda and Wegovy as approved weight-reduction medicines for defined populations. Approval belongs to the product and its labeled use; it does not transfer to every online preparation using the same ingredient name. FDA separately warns about unapproved GLP-1 products. FDA product context · FDA on unapproved products.
When reading the next comparison headline, keep four items together: the medicine studied, the participants, the outcome and the time point. Our tirzepatide versus semaglutide guide applies that approach to a different head-to-head trial. For the formulation question, see oral semaglutide absorption.
Sources & further reading
Research context last reviewed October 7, 2026. Last updated October 7, 2026. Educational reading, not individual medical advice. How this article was prepared.
