GLP-3 Retatrutide vs PlexusDx (2026)

Q: Is "GLP-3" a real hormone?

No. Humans produce GLP-1 and GLP-2; there is no GLP-3. GLP-3 is an informal nickname for retatrutide because the drug targets three receptors (GLP-1, GIP, and glucagon). It is not used by Eli Lilly, the FDA, or any peer-reviewed journal - if a vendor uses the term to sell you product, treat that as a red flag.

Q: How does retatrutide compare to tirzepatide on weight loss?

In Phase 3, retatrutide's 12 mg arm produced approximately 28.7% mean body-weight loss at 68 weeks (TRIUMPH-4); tirzepatide's SURMOUNT-1 produced approximately 22.5% at the 15 mg dose at 72 weeks. Retatrutide also showed substantially higher liver-fat reduction in Phase 2 substudy data. Tirzepatide has lower discontinuation rates, no dysesthesia signal, and is available now - PlexusDx prescribes compounded tirzepatide through Tirzepatide Injection at $249/mo.

Last reviewed: May 12, 2026 Last updated: May 12, 2026

Written by: Jay Hastings , CEO of PlexusDx

Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations. He has more than 20 years of experience across healthcare innovation, genomics, laboratory operations, healthcare investing, and strategic finance. His work has included scaling healthcare startups, leading CLIA lab integrations, and helping expand consumer access to precision health tools.

Medically reviewed by: Jayden Lee, PharmD, EMBA

Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Science Liaison with a PharmD and MBA specializing in pharmacogenomics and clinical product development, with a proven ability to bridge the gap between genomic research and practical patient outcomes. Dr. Lee has more than 10 years of professional experience in clinical pharmacy, academia, and research.

This article is part of the PlexusDx Education Hub — your resource for evidence-based guidance on GLP-1 therapies, weight management protocols, and the genetic variables that shape every metabolic decision. Browse all Peptides & GLP-1 education

If you searched “GLP-3 retatrutide,” here is the short version: there is no human hormone called GLP-3. The label is an internet nickname for retatrutide (research code LY3437943), an investigational once-weekly injectable from Eli Lilly that activates three receptors at once — GLP-1, GIP, and glucagon. Phase 3 results from the TRIUMPH program have generated headline weight-loss numbers, but retatrutide is not FDA-approved, is not legally available for prescription or purchase, and is not eligible for compounding under current FDA enforcement. The earliest realistic approval window is 2027, and that timeline is contingent on the rest of the Phase 3 readouts. This guide explains what retatrutide is, what the trial data actually show, why “GLP-3” is misleading, and how PlexusDx’s currently-available compounded semaglutide and tirzepatide protocols — including Semaglutide Injection, Tirzepatide Injection, Microdose GLP-1 Protocol, and GLP-Squared — compare to the pipeline asset many patients are now asking about.

What “GLP-3” actually means — and why the name is wrong

Humans produce GLP-1 (glucagon-like peptide-1) and GLP-2 (glucagon-like peptide-2). There is no third member of the family. The “GLP-3” tag started circulating on social media and in news headlines as shorthand for a drug that hits three receptor targets, but it is not a scientific term and you will not find it in Eli Lilly’s filings, in the New England Journal of Medicine, or in any FDA document. The drug being discussed is retatrutide, sometimes written as “triple-G” or “triple agonist” in clinical literature. Sellers using the “GLP-3 peptide” phrasing are typically unregulated vendors marketing “research use only” vials — a category the FDA has issued explicit warnings about. When you are evaluating a source, look for the word retatrutide or the code LY3437943; that is the actual name in the regulatory and scientific record.

How retatrutide works: the triple-agonist mechanism

Retatrutide is the third generation in a line of incretin-based weight-loss therapies. The first generation — semaglutide — is a single agonist that activates GLP-1 receptors only; it underpins Wegovy and Ozempic, and it is the active ingredient in PlexusDx’s Semaglutide Injection and Semaglutide Oral protocols. The second generation — tirzepatide — is a dual agonist that activates GLP-1 and GIP receptors; it underpins Mounjaro and Zepbound, and it is the active ingredient in PlexusDx’s Tirzepatide Injection and Tirzepatide Oral protocols. Retatrutide adds a third target: the glucagon receptor. Glucagon agonism increases energy expenditure and is associated in preclinical work with marked liver-fat reduction. The same glucagon activity, however, is what makes the safety profile less predictable than the GLP-1 and GIP/GLP-1 classes that already have years of post-marketing data behind them.

Clinical trial results: what the Phase 2 and Phase 3 data show

The Phase 2 trial published in NEJM (Jastreboff et al., 2023) reported approximately 24.2% mean body-weight loss at 48 weeks on the 12 mg dose, with concurrent 82% liver-fat reduction at 24 weeks reported in a Phase 2 substudy (Sanyal et al., Nature Medicine 2024). Eli Lilly’s December 2025 topline release for TRIUMPH-4 reported a mean ~28.7% body-weight loss (~71 lbs) over 68 weeks at the 12 mg dose — among the largest average reductions reported in any Phase 3 obesity trial to date. TRIUMPH-4 enrolled patients with knee osteoarthritis, so generalization to the broader population still depends on the TRIUMPH-1 readout and the rest of the seven-trial program expected through 2026. Discontinuation rates trended higher than with semaglutide or tirzepatide, and a novel adverse-event signal — dysesthesia — was reported in up to ~21% of participants on the 12 mg dose versus ~0.7% on placebo. None of this changes the headline efficacy story, but it is the reason the FDA approval timeline is not a foregone conclusion.

Retatrutide vs semaglutide vs tirzepatide — how the classes compare

Semaglutide’s pivotal STEP 1 trial reported ~14.9% mean body-weight loss at 68 weeks on the 2.4 mg weekly dose. Tirzepatide’s SURMOUNT-1 reported ~22.5% at the 15 mg weekly dose at 72 weeks. Retatrutide’s TRIUMPH-4 12 mg arm reported ~28.7% at 68 weeks. The efficiency gradient is real, but only two of those three classes are available outside a clinical trial right now — semaglutide and tirzepatide. PlexusDx prescribes both through licensed U.S. compounding pharmacies. Semaglutide Injection runs $149/mo across five weekly dose levels (0.25 mg to 2.0 mg). Tirzepatide Injection runs $249/mo across six weekly dose levels (2.5 mg to 15 mg). For patients who want stacked dual-mechanism therapy without waiting for retatrutide, GLP-Squared pairs compounded semaglutide with compounded tirzepatide across six provider-titrated dose levels at $249/mo. None of these are FDA-approved finished products — only the branded versions (Wegovy, Ozempic, Zepbound, Mounjaro) carry that designation — but they share the same active ingredients that ran the SUSTAIN, STEP, and SURMOUNT trials.

Side effects, safety signals, and the dysesthesia question

Across the GLP-1 receptor agonist class, gastrointestinal side effects (nausea, vomiting, diarrhea, constipation) are the most common; pancreatitis, gallbladder disease, and acute kidney injury are less common but documented. The boxed warning for thyroid C-cell tumors based on rodent studies applies to BOTH semaglutide and tirzepatide. Retatrutide adds a glucagon-driven elevation in heart rate and the dysesthesia signal mentioned above — abnormal skin sensations (tingling, burning, or altered touch perception) that have not been reported at material rates with either semaglutide or tirzepatide. The dysesthesia rate on 12 mg in TRIUMPH-4 (~20.9%) versus placebo (~0.7%) is the kind of finding regulators ask follow-up questions about, and it is one reason the 4 mg maintenance dose is being studied separately. None of this means retatrutide will fail to reach approval — it means the safety package will get extra scrutiny on the way there.

Is retatrutide FDA-approved? Compounding status and the “research peptide” trap

No. Retatrutide is investigational. The TRIUMPH Phase 3 program has seven readouts expected in 2026, with the earliest realistic FDA filing late 2026 and approval no sooner than 2027. Compounding is also not a workaround: the FDA has issued warning letters stating that compounded retatrutide products are unapproved new drugs and misbranded, and retatrutide is not eligible for compounding under the 503A or 503B exemptions that govern legitimate pharmacy-prepared semaglutide and tirzepatide. Online vendors selling “retatrutide peptide” or “GLP-3” vials marketed as “research use only” are operating outside the regulatory framework — purity, dosage accuracy, and sterility are unverified, and the FDA has issued explicit consumer warnings. The only legitimate way to access retatrutide today is enrollment in a TRIUMPH trial through ClinicalTrials.gov.

How PlexusDx fits if you don’t want to wait

Most patients reading about retatrutide are not in a position to enroll in a clinical trial — eligibility criteria are narrow (BMI thresholds, comorbidities, geographic proximity to a study site), and the trial timelines run years. The pragmatic alternative is a currently-available compounded GLP-1 protocol with a real prescribing clinician and a measurable genetic baseline. PlexusDx Weight Management Protocols cover four mechanism classes across six compounded products: Microdose GLP-1 Protocol at $129/mo flat (capsule, troche, lozenge, or sublingual delivery), Semaglutide Oral from $249/mo across six daily dose levels (3 mg to 24 mg), Semaglutide Injection at $149/mo, Tirzepatide Injection at $249/mo, Tirzepatide Oral at $279/mo across seven daily dose levels (5 mg to 25 mg), and GLP-Squared at $249/mo for stacked dual-compound therapy. All protocols are all-inclusive (async clinician consult, prescription, compounded medication, shipping), cash-pay with no membership fee, and available in all 50 states (five require a scheduled live consult instead of async intake).

Why genetics matter when you’re comparing options

Whether you eventually start retatrutide or you start a semaglutide or tirzepatide protocol now, individual response varies. Variants in GLP1R, GIPR (rs1800437 in particular), FTO, MC4R, and TCF7L2 are associated with differential response patterns to GLP-1 receptor agonists and dual agonists. The Precision Peptide Genetic Test maps 48 genes and 57 variants across 14 health pathways, including 34 weight-management insights. Standalone pricing is $298; as a $99 add-on after your first month on any PlexusDx protocol, it gives the prescribing clinician a measurable starting point for titration decisions rather than a population-average titration schedule. If retatrutide does reach approval, the same baseline informs whether a triple-agonist is likely to fit your biology or whether a single or dual agonist is the better mechanism class for you specifically.

Cost picture: what retatrutide will likely cost vs PlexusDx today

Lilly has not announced retatrutide pricing — that decision will follow approval. For class reference, Wegovy lists at approximately $1,349/mo (about $349/mo through Novo Nordisk’s self-pay program), and Zepbound lists at approximately $1,086/mo (with $249-$369/mo Lilly Direct self-pay vials). Retatrutide pricing will likely be benchmarked against those figures. Today, PlexusDx’s annualized cost on the entry tier — Microdose GLP-1 Protocol at $129/mo — is $1,548/year. Semaglutide Injection runs $2,148–$2,748/year. Tirzepatide Injection runs $2,748–$3,708/year. GLP-Squared runs $2,148–$3,900/year. None of those are FDA-approved finished drugs, but they are available now, in all 50 states, with no membership fee. Pricing as of April 2026.

Frequently asked questions

Is “GLP-3” a real hormone?

No. Humans produce GLP-1 and GLP-2; there is no GLP-3. “GLP-3” is an informal nickname for retatrutide because the drug targets three receptors (GLP-1, GIP, and glucagon). It is not used by Eli Lilly, the FDA, or any peer-reviewed journal — if a vendor uses the term to sell you product, treat that as a red flag.

Is retatrutide FDA-approved or available by prescription?

No. Retatrutide is investigational and in Phase 3 trials. The earliest realistic FDA approval is estimated for 2027 and is not confirmed by Lilly or the FDA. The only legitimate access today is enrollment in a TRIUMPH clinical trial through ClinicalTrials.gov. PlexusDx does not prescribe retatrutide.

Can PlexusDx prescribe compounded retatrutide?

No. The FDA has issued warning letters stating compounded retatrutide products are unapproved new drugs and misbranded. PlexusDx prescribes only compounded semaglutide and tirzepatide, which are eligible for licensed pharmacy compounding. If you want a currently-available GLP-1 option, see Semaglutide Injection, Tirzepatide Injection, or GLP-Squared.

How does retatrutide compare to tirzepatide on weight loss?

In Phase 3, retatrutide’s 12 mg arm produced ~28.7% mean body-weight loss at 68 weeks (TRIUMPH-4); tirzepatide’s SURMOUNT-1 produced ~22.5% at the 15 mg dose at 72 weeks. Retatrutide also showed substantially higher liver-fat reduction in Phase 2 substudy data. Tirzepatide has lower discontinuation rates, no dysesthesia signal, and is available now — PlexusDx prescribes compounded tirzepatide through Tirzepatide Injection at $249/mo.

What is dysesthesia and why does it matter?

Dysesthesia is an abnormal touch sensation — tingling, burning, or altered skin perception. It was reported in up to ~20.9% of TRIUMPH-4 participants on the 12 mg dose versus ~0.7% on placebo. Most cases were mild, but the signal has not been seen at material rates with semaglutide or tirzepatide, and regulators will scrutinize it across the rest of the Phase 3 program.

Can I buy retatrutide as a “research peptide” online?

No. The FDA has issued explicit warnings against unapproved retatrutide products marketed as “research use only.” These products have unverified purity, dosage accuracy, and sterility, and the agency has sent warning letters to companies selling compounded retatrutide. Buying outside a clinical trial is not legal and is not safe.

What should I do now if I want to lose weight and don’t want to wait for retatrutide?

Compare PlexusDx’s currently-available GLP-1 protocols against your eligibility and budget. Microdose GLP-1 Protocol is the entry tier at $129/mo flat. Semaglutide Injection ($149/mo) and Tirzepatide Injection ($249/mo) cover the two mechanism classes with the most clinical evidence. Add the Precision Peptide Genetic Test ($99 as an add-on after month one) so dose decisions are anchored to your biology. If retatrutide reaches approval, switching is always an option.

GLP-3 Retatrutide Explained (2026): Pipeline Triple-Agonist vs PlexusDx GLP-1 Options Available Today | PlexusDx