ONE SIGNAL01
SEMAGLUTIDE
GLP-1
The simplest pathway of the three.
APPROVED MEDICINES EXIST
BEGINNER'S GUIDE / METABOLIC SIGNALING
SAME FAMILY.
DIFFERENT SIGNALS.
Think of receptors like biological switches. Semaglutide activates one switch, tirzepatide activates two, and retatrutide activates three.
TWO SIGNALS02
TIRZEPATIDE
GIP+GLP-1
Adds a second metabolic signal.
APPROVED MEDICINES EXIST
THREE SIGNALS03
RETATRUTIDE
GIP+GLP-1+GLUCAGON
Adds a third signal and remains under investigation.
INVESTIGATIONAL — NOT FDA APPROVED
01 / THE ESSENTIALS
THREE THINGS TO REMEMBER.
- 1Related does not mean interchangeable.
- 2Semaglutide and tirzepatide have approved medicines. Retatrutide is still investigational.
- 3More receptor targets do not automatically guarantee better results.
02 / START WITH THE BIG PICTURE
APPETITE IS ONLY PART OF THE STORY.
Semaglutide, tirzepatide, and retatrutide are discussed together because each interacts with hormone-receptor systems involved in metabolic signaling. Those systems help coordinate how the body responds to food, manages glucose, communicates fullness, and handles stored energy.
The molecules are related, but they are not interchangeable. Each has a different receptor profile, a different evidence history, and a different regulatory status.
03 / THE THREE SIGNALS
WHAT DO GLP-1, GIP, AND GLUCAGON ACTUALLY DO?
These summaries describe the receptor systems at a high level. Their effects depend on tissue, physiological context, exposure, and study population.
01
GLP-1
THE SATIETY AND GLUCOSE SIGNAL
GLP-1 receptor signaling participates in glucose-dependent insulin release, glucagon regulation, gastric emptying, and appetite-related signaling. It is the shared pathway across all three molecules.
02
GIP
THE SECOND INCRETIN SIGNAL
GIP receptor signaling also responds to nutrient intake and contributes to glucose-dependent insulin signaling. Tirzepatide and retatrutide add this pathway to GLP-1 activity.
03
GLUCAGON
THE ENERGY-MOBILIZATION SIGNAL
Glucagon receptor signaling is involved in hepatic glucose output and energy metabolism. Retatrutide adds this pathway, which is one reason its full benefit-risk profile requires dedicated clinical study.
THE IMPORTANT DISTINCTION:Target count describes mechanism. It does not, by itself, establish superiority, safety, or the right outcome for a particular population.
04 / THE THREE MOLECULES
SAME CONVERSATION. THREE DIFFERENT EVIDENCE STORIES.
01ONE RECEPTOR TARGET
SEMAGLUTIDE
THE ESTABLISHED GLP-1 REFERENCE POINT.
Semaglutide is a GLP-1 receptor agonist. FDA-approved semaglutide medicines have been evaluated through multiple large clinical programs, giving researchers a substantial human evidence base across defined indications.
- RECEPTOR PROFILE
- GLP-1
- RESEARCH CONTEXT
- Appetite signaling, glucose regulation, body-weight outcomes, cardiovascular outcomes, and metabolic liver disease
- U.S. STATUS
- FDA-approved medicines exist for specific indications
- KEY LIMIT
- Approval of a medicine does not validate a separately supplied research material
02TWO RECEPTOR TARGETS
TIRZEPATIDE
A DUAL INCRETIN APPROACH.
Tirzepatide is a dual GIP and GLP-1 receptor agonist. Its research program asks what changes when two incretin pathways are engaged within one molecule rather than GLP-1 alone.
- RECEPTOR PROFILE
- GIP + GLP-1
- RESEARCH CONTEXT
- Glucose regulation, appetite and body-weight outcomes, metabolic health, and obstructive sleep apnea in adults with obesity
- U.S. STATUS
- FDA-approved medicines exist for specific indications
- KEY LIMIT
- Its two-target mechanism cannot be reduced to “twice” the effect of GLP-1 signaling
03THREE RECEPTOR TARGETS
RETATRUTIDE
THE INVESTIGATIONAL TRIPLE AGONIST.
Retatrutide engages GIP, GLP-1, and glucagon receptors. Five Phase 3 datasets had been disclosed by its sponsor as of this review, while additional studies and regulatory work remained ongoing.
- RECEPTOR PROFILE
- GIP + GLP-1 + glucagon
- RESEARCH CONTEXT
- Obesity, type 2 diabetes, cardiometabolic outcomes, sleep apnea, osteoarthritis-related endpoints, and liver-related research
- U.S. STATUS
- Investigational; not FDA approved
- KEY LIMIT
- Sponsor-reported topline results do not replace full peer review and regulatory evaluation
05 / SIDE-BY-SIDE
COMPARE THE MECHANISMS, EVIDENCE, AND LIMITS.
Trial results only make sense when the population, dose, duration, comparator, and endpoint are considered together.
| COMPARISON POINT | SEMAGLUTIDE | TIRZEPATIDE | RETATRUTIDE |
|---|---|---|---|
| Primary receptor profile | GLP-1 | GIP + GLP-1 | GIP + GLP-1 + glucagon |
| Evidence classification | ESTABLISHED Multiple Phase 3 programs and regulated use | ESTABLISHED Multiple Phase 3 programs and regulated use | INVESTIGATIONAL Peer-reviewed Phase 2 evidence plus disclosed Phase 3 datasets |
| U.S. regulatory context | FDA-approved semaglutide medicines have defined indications | FDA-approved tirzepatide medicines have defined indications | Not FDA approved; sponsor reported that its clinical package could support global submissions |
| Direct comparative evidence | A 2025 randomized head-to-head obesity trial directly compared tirzepatide with semaglutide in adults without diabetes | No completed randomized head-to-head trial against both marketed comparators was available for this review | |
| What remains important | Long-term outcomes, population-specific effects, tolerability, and maintenance | Long-term outcomes, population-specific effects, tolerability, and maintenance | Full peer-reviewed Phase 3 reporting, long-term safety, regulatory review, and comparative effectiveness |
06 / WHAT THE RESEARCH ACTUALLY SAYS
THREE EVIDENCE STORIES.
SEMAGLUTIDE
STEP 1 was a randomized, double-blind Phase 3 trial in 1,961 adults with overweight or obesity without diabetes. It established clinically meaningful weight reduction with semaglutide 2.4 mg plus lifestyle intervention over 68 weeks.
TIRZEPATIDE
SURMOUNT-1 randomized 2,539 adults with obesity or overweight without diabetes. Later, SURMOUNT-5 provided direct randomized evidence comparing tirzepatide with semaglutide rather than relying only on separate trials.
RETATRUTIDE
Peer-reviewed Phase 2 trials reported dose-dependent changes in body weight and metabolic endpoints. Lilly subsequently announced positive 2026 Phase 3 topline results, but topline announcements are not a substitute for complete peer-reviewed reporting and regulatory review.
08 / BEGINNER FAQ
THE QUESTIONS PEOPLE ASK FIRST.
ARE THESE THREE COMPOUNDS THE SAME THING?+
No. They overlap at the GLP-1 receptor, but tirzepatide adds GIP receptor activity and retatrutide adds both GIP and glucagon receptor activity. Their clinical evidence and regulatory status also differ.
DOES THREE RECEPTOR TARGETS AUTOMATICALLY MEAN “BETTER”?+
No. Receptor count describes a mechanism—not a guaranteed outcome. Benefit, risk, tolerability, dose, study duration, and population all have to be evaluated with actual data.
IS RETATRUTIDE FDA APPROVED?+
No. As of September 2026, retatrutide remains investigational and is not FDA approved. Its sponsor has disclosed data from five Phase 3 trials, with additional development and regulatory evaluation still required.
CAN RESULTS FROM THREE SEPARATE TRIALS BE RANKED DIRECTLY?+
Not reliably. Separate trials may use different participants, durations, endpoints, doses, estimands, and missing-data methods. Direct randomized comparisons provide stronger comparative evidence.
IS “GLP-3” THE SCIENTIFIC NAME FOR RETATRUTIDE?+
No. “GLP-3” is an informal and scientifically inaccurate nickname. Retatrutide is more accurately described as a GIP, GLP-1, and glucagon triple receptor agonist.
DO APPROVED MEDICINES VALIDATE RESEARCH MATERIALS WITH THE SAME NAMED MOLECULE?+
No. Published findings and FDA approval concern the specifically studied or regulated medicine. They do not establish the identity, purity, sterility, bioequivalence, safety, or effectiveness of a separate research material.
09 / CONTINUE THE RESEARCH
MOVE FROM COMPARISON TO DOCUMENTATION.
Use the individual research profiles to review each molecule on its own terms—including mechanism, research context, limitations, related literature, and available product documentation.
10 / SOURCES & FURTHER READING
READ THE ACTUAL WORK.
Primary and authoritative sources prioritized.
- WEGOVY (semaglutide) Prescribing InformationFDA LABEL ↗
U.S. Food and Drug Administration. Current mechanism and regulatory labeling.
- ZEPBOUND (tirzepatide) Prescribing InformationFDA LABEL ↗
U.S. Food and Drug Administration. Current mechanism and regulatory labeling.
- Once-Weekly Semaglutide in Adults with Overweight or ObesityPUBMED ↗
Wilding JPH, et al. N Engl J Med. 2021;384:989–1002. STEP 1. PMID 33567185.
- Tirzepatide Once Weekly for the Treatment of ObesityPUBMED ↗
Jastreboff AM, et al. N Engl J Med. 2022;387:205–216. SURMOUNT-1. PMID 35658024.
- Tirzepatide as Compared with Semaglutide for the Treatment of ObesityPUBMED ↗
Aronne LJ, et al. N Engl J Med. 2025. SURMOUNT-5. PMID 40353578.
- Triple-Hormone-Receptor Agonist Retatrutide for ObesityPUBMED ↗
Jastreboff AM, et al. N Engl J Med. 2023;389:514–526. Phase 2. PMID 37366315.
- TRIUMPH-1 Phase 3 Study RecordTRIAL RECORD ↗
ClinicalTrials.gov NCT05929066. Registered study design and status.
- TRIUMPH-1 Topline Phase 3 ResultsSPONSOR RELEASE ↗
Eli Lilly and Company, May 21, 2026. Sponsor-reported topline results; not treated here as a substitute for peer-reviewed publication.
- Retatrutide Phase 3 Development UpdateSPONSOR RELEASE ↗
Eli Lilly and Company, July 23, 2026. Sponsor-reported TRIUMPH-2 and TRIUMPH-3 topline results and current development context.
Source hierarchy: regulatory documents and registered trials first; peer-reviewed human studies second; sponsor topline disclosures clearly labeled. Study findings concern named investigational or regulated medicines and do not independently validate any Ethos research product.
EDITORIAL STANDARD
SHOW THE WORK. LABEL THE LIMITS.
Prepared by the Ethos Bioscience research-content team using FDA documents, registered clinical trials, peer-reviewed publications, and clearly labeled sponsor disclosures. Human and investigational evidence are separated, and the page is dated so readers can see when the review occurred.