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From cells to people: understand the research stages
A promising mechanism, an animal experiment and a human trial answer different questions. Here is how to tell which kind of evidence you are reading.
Peptide science,
explained simply.
Clear guides to 38 peptides, the latest research news and doctors’ videos, so you can see what’s proven and what isn’t.
Results
What the weight-loss trials found.
Average weight lost in the main published trials of today’s leading medicines, each compared with a placebo.
Each medicine compared with a placebo in its own trial. Ordered by reported average; this is not a head-to-head ranking.
- Medicine
- Placebo
Retatrutide · Experimental
12 mg weekly
Phase 2 · 48 weeks · 338 people
24.2%
2.1%
Tirzepatide · Approved
15 mg weekly (Zepbound)
SURMOUNT-1 · 72 weeks · 2,539 people
20.9%
3.1%
Semaglutide · Approved
2.4 mg weekly injection (Wegovy)
STEP 1 · 68 weeks · 1,961 people
14.9%
2.4%
Semaglutide · Approved (US)
25 mg daily pill (Wegovy pill)
OASIS 4 · 64 weeks · 307 people
13.6%
2.2%
Average body weight lost
Each human trial had different people, doses and lengths, so compare with care. The bars describe approved or experimental medicines studied under medical supervision with diet and exercise advice, not laboratory research products. They use full journal reports; conference findings and different endpoints appear separately below.
Show these numbers as a table
| Medicine | Trial | People | Weeks | Medicine | Placebo | Source |
|---|---|---|---|---|---|---|
| Retatrutide, 12 mg weekly | Phase 2 | 338 | 48 | 24.2% | 2.1% | PubMed |
| Tirzepatide, 15 mg weekly (Zepbound) | SURMOUNT-1 | 2,539 | 72 | 20.9% | 3.1% | PubMed |
| Semaglutide, 2.4 mg weekly injection (Wegovy) | STEP 1 | 1,961 | 68 | 14.9% | 2.4% | PubMed |
| Semaglutide, 25 mg daily pill (Wegovy pill) | OASIS 4 | 307 | 64 | 13.6% | 2.2% | PubMed |
PTT-A and CBL-514: evidence so far
Neither has a comparable average human body-weight-loss result in the research below. Animal body weight and human fat volume measure different things, so they are shown separately from the bars.
Animal research · conference abstract
PTT-A
- Average human body-weight loss
- Not established in the cited research
- What was measured
- Body weight in diet-induced obese rats over 21 days
- Reported finding
- Body weight was 19.2% lower versus vehicle at the higher studied exposure; tirzepatide was 12.1% lower versus vehicle in the same experiment.
A difference versus vehicle in rats is not average weight lost by people. It cannot establish superiority to retatrutide in humans.
Human fat-volume subgroup · conference report
CBL-514
- Average human body-weight loss
- Not established by this fat-volume result
- What was measured
- MRI-measured visceral-fat volume, four weeks after final treatment
- Reported finding
- Visceral-fat volume fell 12.01%; placebo rose 5.68%. The small phase 2 subgroup had 40 participants with later follow-up data.
12.01% less visceral fat is not 12.01% less body weight. CBL-514 is an experimental small molecule, not a peptide.
News & articles
New research, explained.
Recent studies and decisions, written so anyone can follow them, with every source linked.
GuideReading the evidence
Body weight, fat and muscle: read the right result
A percentage means little without its denominator. Learn why changes in body weight, a fat deposit and a measurement in rats belong in different comparisons.
StudyWeight management
PTT-A targets four receptors. The evidence is still in animals
The experimental peptide combines GLP-1, GIP, amylin and calcitonin activity. Here is what the original research can tell us about weight loss.
GuideRecovery & mobility
BPC-157 has dozens of animal studies. The human evidence fits on one page
A 2025 systematic review found 35 preclinical studies and a single clinical one. Here is what the few human reports did, and did not, show.
Videos
Doctors explain.
Hand-picked videos, mostly from doctors, including some skeptical ones.
Nick Norwitz
The science behind Ozempic and other GLP-1 medications
How GLP-1 medicines work in the gut and brain, in clear language.
Nick Norwitz, MD, PhD
Watch on YouTubePeter Attia MD
Pros and cons of GLP-1 weight-loss drugs
Two doctors weigh the benefits against the downsides, including muscle loss and cost.
Peter Attia, MD, with diabetes researcher Ralph DeFronzo, MD
Watch on YouTubeDoctor Mike
Exposing the truth about peptides
A practicing doctor looks at the peptide trend and separates the evidence from the hype.
Mikhail Varshavski, DO, family medicine physician
Watch on YouTubeShop
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