What does 15 percent weight loss mean?

It means losing 15 pounds for every 100 pounds of starting weight. A person starting at 220 pounds would lose 33 pounds and weigh 187 pounds. The percentage is simple arithmetic; it does not predict how quickly the loss happens, where it comes from on the body or which other health measures will change.

How many STEP 1 participants lost at least 15 percent?

Just over half did. At 68 weeks, 50.5% of participants assigned to semaglutide had lost at least 15% of their starting weight, compared with 4.9% assigned to placebo. The semaglutide group's average was 14.9%, so the trial included people both well above and well below that headline number.

Does 15 percent weight loss mean five inches off the waist?

Not necessarily. The STEP 1 semaglutide group averaged a 13.54 cm waist reduction, about 5.3 inches, while averaging 14.9% weight loss. That was a group result, not a fixed conversion. Waist change varies by starting measurements and body-fat distribution, and the study did not translate centimeters into clothing sizes.

What health measures changed in STEP 1?

The semaglutide group had larger average reductions than placebo in waist circumference, systolic blood pressure, HbA1c, triglycerides and C-reactive protein at 68 weeks. Participants also reported better physical function on two questionnaires. These measures came from the full trial groups, so they cannot be assigned automatically to every person who reaches 15% weight loss.

Will everyone lose 15 percent with semaglutide?

No. STEP 1 reported a 14.9% group average, while 50.5% of semaglutide participants reached at least 15% and the rest did not. The study followed adults without diabetes for 68 weeks alongside lifestyle support. Starting health, treatment duration, tolerated dose, other medicines and individual biology can all move a result away from that average.

15 Percent Weight Loss: What the Numbers Show

15 percent weight loss means 15 pounds for every 100 pounds of starting weight. For someone starting at 220 pounds, it is 33 pounds, taking the scale to 187. In STEP 1, the average loss with semaglutide was 14.9% over 68 weeks—close enough to make 15% the useful shorthand. But it was a group average, not a forecast, and it did not look the same for everyone.

What 15 percent weight loss means in pounds

The calculation is starting weight multiplied by 0.15. It is a proportion, so the number of pounds changes with the starting point.

Starting weight	15% of that weight	Weight after that loss
180 lb	27 lb	153 lb
220 lb	33 lb	187 lb
260 lb	39 lb	221 lb
300 lb	45 lb	255 lb

STEP 1 was a randomized trial, meaning its 1,961 adults were assigned by chance to semaglutide or placebo (an inactive injection). Everyone also received lifestyle support. Participants had obesity, or overweight with a related health condition, and none had diabetes.

At week 68, the semaglutide group averaged 14.9% weight loss, compared with 2.4% for placebo. Just over half of the semaglutide group—50.5%—lost at least 15%. That split matters: an average near 15% does not mean everyone landed there. The broader semaglutide weight-loss results page follows the full range. (Wilding et al., New England Journal of Medicine, 2021)

What changed besides weight in STEP 1

The study measured more than the scale. These are averages for the full assigned groups, not a list of changes that every person who lost 15% experienced.

Measure at 68 weeks	Semaglutide group	Placebo group	In everyday words
Waist circumference	−13.54 cm	−4.13 cm	About 5.3 inches versus 1.6 inches
Systolic blood pressure	−6.16 mm Hg	−1.06 mm Hg	About six points versus one point on the top number
HbA1c	−0.45 percentage points	−0.15 points	A small shift in average blood sugar over two to three months
Triglycerides	−21.9%	−7.3%	A larger drop in this blood fat
C-reactive protein	−53%	−15%	A larger drop in CRP, a marker of inflammation

The waist figure is real, but it cannot be converted into a clothing size. Brands size clothes differently, bodies lose from different places, and the trial did not record that outcome.

The blood-pressure result also needs scale. A six-point group average is meaningful data, but it is not a reason to change blood-pressure medicine without the clinician who prescribed it. STEP 1 found favorable changes in several markers; it did not prove that reaching exactly 15% causes each one.

Physical function was something people reported

STEP 1 used two questionnaires about daily physical function. On the SF-36 physical-function scale, the average change was 2.21 points with semaglutide and 0.41 with placebo. On the weight-focused IWQOL scale, it was 14.67 points versus 5.25. Higher scores meant people reported functioning better.

A later analysis made those scores easier to read. A meaningful improvement was reported by 39.8% of the semaglutide group versus 24.1% of the placebo group on SF-36, and by 51.8% versus 28.3% on the weight-focused measure. These were questionnaire responses, not direct tests of strength or walking speed. (Rubino et al., Diabetes, Obesity and Metabolism, 2024)

The 15 percent mark also appeared with tirzepatide

SURMOUNT-1 tested tirzepatide, a medicine that acts on two gut-hormone signals involved in appetite and blood sugar. At the 5 mg maintenance dose studied, the group averaged 15.0% weight loss over 72 weeks. Its waist circumference fell by an average of 14.0 cm, compared with 4.0 cm for placebo. Higher-dose results belong in the broader tirzepatide weight-loss results guide; the useful point here is that another trial reached a similar 15% landmark with a different medicine and timeline. (Jastreboff et al., New England Journal of Medicine, 2022)

SURMOUNT-OSA asked a narrower question in adults with obesity and moderate-to-severe obstructive sleep apnea. AHI, the number of breathing pauses or shallow breaths per hour of sleep, fell by 25.3 events per hour with tirzepatide versus 5.3 with placebo in the trial without positive-airway-pressure therapy. In the separate trial of people already using that therapy, the drops were 29.3 versus 5.5 events per hour. Those results describe people with diagnosed sleep apnea, not everyone who loses 15%. (Malhotra et al., New England Journal of Medicine, 2024)

Knee pain had its own measurement

STEP 9 enrolled 407 adults with obesity and moderate-to-severe knee osteoarthritis pain. At 68 weeks, average weight change was −13.7% with semaglutide and −3.2% with placebo.

Pain was scored on the 100-point WOMAC scale, where a lower number means less reported pain. The average change was −41.7 points with semaglutide and −27.5 with placebo. SF-36 physical function rose 12.0 points versus 6.5. This does not show what happens to a knee without osteoarthritis, and a symptom score is not proof that joint tissue was repaired. It shows what this particular trial measured in this particular group. (Bliddal et al., New England Journal of Medicine, 2024)

A fresh check on the headline number

As of September 9, 2026, the day this article was written, an updated analysis published August 29, 2026 combined nine semaglutide trials with 6,239 adults. Compared with placebo, the combined averages were 12.04 percentage points more weight loss, 9.36 cm more waist reduction and a 40.9% larger CRP drop. Results differed considerably among trials, and one study of a higher dose accounted for some of that variation. That is the clearest reason to treat 15% as a research landmark, not a personal deadline. (Milluzzo et al., International Journal of Obesity, 2026)

What the number cannot decide

A percentage cannot say which medicine fits, whether a health marker will move, or how a person will feel. The trials above studied branded medicines under research protocols. They do not test Promise's compounded formulations.

Through Promise, semaglutide is dispensed as a compounded medication, which is different from an FDA-approved product: the formulation offered here is not FDA-approved. A compounded medication is prepared by a licensed U.S. compounding pharmacy for an individual prescription. A licensed provider may still prescribe a compounded formulation; that decision belongs to the patient and doctor.

At Promise, a licensed provider reviews every request and not everyone qualifies. The useful conversation puts the percentage beside medical history, current medicines, side effects and the measures that matter for that person's health.