An education-first walkthrough of retatrutide (LY3437943), the triple GLP-1/GIP/glucagon agonist. Covers the Phase 2 NEJM trial data at 24 and 48 weeks, the trial titration schedule, side effects, reconstitution, and honest sourcing. Research-use-only, not FDA-approved, not medical advice.
retatrutide is the compound everyone in the peptide world keeps asking about, and most of what's written on it is either hype or a wall of made-up numbers. this is the corrected version. everything trial-derived here traces back to one source: the Phase 2 study Jastreboff and colleagues published in NEJM in 2023 PMID: 37366315 (DOI). where a number isn't in that trial, i say so, or i cut it.
one thing up front, repeated on purpose: retatrutide is a research compound. it is NOT FDA-approved. Phase 3 (TRIUMPH) is still running. nothing below is medical advice or a prescription. it's a report on what the trial did and what the research community describes. talk to a licensed clinician before you do anything with this.
what retatrutide actually is
retatrutide, developed by Eli Lilly and known in the literature as LY3437943, is a single-molecule triple agonist. it hits three receptors at once: GLP-1, GIP, and glucagon. that third one is what sets it apart. semaglutide is a GLP-1 agonist. tirzepatide is a dual GLP-1/GIP agonist. retatrutide adds glucagon-receptor activity on top, which is why people describe it as the follow-on to tirzepatide from the same lab.
if you want the head-to-head framing, we keep two comparisons updated: retatrutide vs tirzepatide and retatrutide vs semaglutide. the compound overview lives at /compound/retatrutide.
the phase 2 trial data
here's the study in one breath. it was a Phase 2, double-blind, randomized, placebo-controlled trial of 338 adults with obesity (51.8% men), given once-weekly subcutaneous retatrutide or placebo for 48 weeks. the primary endpoint was percent body-weight change at 24 weeks. registered as NCT04881760, funded by Eli Lilly PMID: 37366315.
these are the 24-week primary-endpoint numbers, the ones the trial was actually designed to measure:
Placebo (24 wk)
-1.6%
primary endpoint
1 mg (24 wk)
-7.2%
primary endpoint
4 mg (24 wk)
-12.9%
primary endpoint
8 mg (24 wk)
-17.3%
primary endpoint
12 mg (24 wk)
-17.5%
primary endpoint
by 48 weeks, with full titration, the separation widened. these are the least-squares mean weight changes at week 48 PMID: 37366315:
Placebo (48 wk)
-2.1%
48 weeks
1 mg (48 wk)
-8.7%
48 weeks
4 mg (48 wk)
-17.1%
48 weeks
8 mg (48 wk)
-22.8%
48 weeks
12 mg (48 wk)
-24.2%
48 weeks
averages hide the spread, so here's the responder data instead, which is more honest about what people actually experienced. this is the share of participants hitting each weight-loss threshold at 48 weeks PMID: 37366315:
| Dose | >=5% loss | >=10% loss | >=15% loss |
|---|---|---|---|
| Placebo | 27% | 9% | 2% |
| 4 mg | 92% | 75% | 60% |
| 8 mg | 100% | 91% | 75% |
| 12 mg | 100% | 93% | 83% |
note what's NOT in that table: no >=20%, >=25%, or >=30% responder rates. the trial didn't report them, so i'm not going to invent them. if you've seen those figures floating around, they weren't from this study.
why the glucagon receptor matters
the glucagon angle
the trial dose schedule
this is where most write-ups go wrong, so read the framing. what follows is the schedule the TRIAL used, plus what the research community commonly reports. it is not a set of instructions for you to dose yourself.
in the trial, retatrutide was given once weekly by subcutaneous injection, escalated in roughly four-week steps PMID: 37366315. the maintenance arms were 4, 8, and 12 mg weekly. importantly, the study found that a 2 mg initial dose (rather than starting at 4 mg) partially mitigated gastrointestinal side effects. so the slow start wasn't cosmetic. it changed tolerability.
the common titration pattern researchers describe mirrors that: start at 2 mg weekly, hold for about four weeks, then step up (2 -> 4 -> 8 -> 12 mg) with roughly four weeks at each level, moving to the next step only if the current one is tolerated.
don't skip the steps - community reports, anecdotal
reconstitution & handling
retatrutide ships as a lyophilized powder and has to be reconstituted before anything else. treat this as lab handling, not a kitchen task. run the numbers through our reconstitution calculator so your concentration math is right before you touch the vial.
the general handling picture: reconstitute with bacteriostatic water, add it slowly against the vial wall rather than blasting it onto the powder, and let it dissolve without shaking. swirl gently if you need to. store reconstituted solution refrigerated. don't shake it, and don't leave it out at room temperature longer than necessary. exact volumes depend on your vial size and target concentration, which is exactly what the calculator is for.
what the trial and community report over time
people want a week-by-week timeline. here's the honest split between what the trial actually measured and what the community anecdotally describes.
from the trial: weight loss accelerated over the full 48 weeks, and the curves for the higher doses hadn't clearly flattened by the end, which is part of why the 48-week numbers beat the 24-week ones PMID: 37366315. gastrointestinal effects clustered around dose increases, and heart-rate changes peaked around 24 weeks before declining PMID: 37366315. those are the load-bearing time-course facts, and they're all i'll state as trial data.
anecdotal community reports - not trial data, unvalidated
side effects
the most common adverse events in the trial were gastrointestinal: nausea and related GI complaints. they were dose-related and mostly mild to moderate PMID: 37366315. the 2 mg start existed specifically to blunt them. the other notable signal was heart rate: dose-dependent increases that peaked at around 24 weeks and then declined PMID: 37366315.
that's the trial-verified safety picture. i'm not going to hand you a fake "85% tolerated it" stat or an invented bpm number, because the trial didn't frame it that way.
community management tips - anecdotal, not medical advice
what the evidence supports
strip out the hype and here's what actually stands: in a Phase 2 trial, retatrutide produced dose-dependent weight loss up to about -24.2% at 48 weeks on 12 mg, and at that dose 100% of participants lost at least 5%, 93% lost at least 10%, and 83% lost at least 15% PMID: 37366315. that's a strong Phase 2 signal.
the real-world caveat: this was a controlled trial with a fixed schedule, a supported population, and 48 weeks of follow-up. it is not FDA-approved, Phase 3 is still running, and long-term safety and durability aren't settled. real-world use with unregulated research material is a different situation from a monitored study, and the results people see won't line up neatly with trial averages.
stack pairings
most stacking questions land in the same place: pairing a GLP-1-class compound with something aimed at body composition or a specific goal. we walk through one common approach in the ultimate shred stack (retatrutide + tesamorelin) protocol. i'm keeping this section general on purpose, since stacking multiplies the unknowns and none of it is validated in the retatrutide trial. if you're already on tirzepatide, the tirzepatide-to-retatrutide switch protocol covers that transition, and if you've stalled, the GLP-1 plateau breakthrough protocol is the relevant read.
where to source
prices move, so the live comparison is the source of truth: check /compound/retatrutide for current vendor pricing, which updates there.
on honest numbers: retatrutide is typically sold as roughly 10 mg vials, and across vetted vendors a single 10 mg vial tends to run around $120. i'm not going to hand you a per-mg figure or a "48-week course total," because those get abused. do the arithmetic yourself if you want. a 12 mg/week schedule is a lot of milligrams over a long run, which is many vials, which is real money, not the pocket-change totals some sites invent.
for a vetted starting point, BHG Labs stocks retatrutide as BHG-3R 10mg, with a COA published per lot. use code REDDIT for 10% off.
affiliate disclosure
whatever you buy, verify the COA before you trust the vial. our how to read a peptide COA guide walks through what actually matters on the certificate, and the vendor scorecard is where we track who's been consistent.
when to cycle off
there's no trial-defined "cycle" for retatrutide. the study ran a continuous 48 weeks. so anything about cycling off is community practice, not evidence.
cycling off - community patterns, anecdotal
Frequently Asked Questions
how much weight did people lose in the trial?
at 48 weeks, least-squares mean weight change was about -24.2% on 12 mg versus roughly -2.1% on placebo. at the 24-week primary endpoint it was about -17.5% on 12 mg versus -1.6% placebo PMID: 37366315.
is retatrutide FDA-approved?
no. it's a research compound. Phase 3 (TRIUMPH) is ongoing. everything here is education, not medical advice.
what dose did the trial use?
once-weekly subcutaneous, titrated from a 2 mg start up through 4, 8, and 12 mg maintenance in roughly four-week steps. the 2 mg start partially reduced GI side effects versus a 4 mg start PMID: 37366315.
what are the main side effects?
gastrointestinal effects were most common, dose-related, and mostly mild to moderate. heart-rate increases peaked around 24 weeks then declined PMID: 37366315.
how is it different from tirzepatide?
tirzepatide is a dual GLP-1/GIP agonist; retatrutide adds glucagon-receptor agonism as a triple agonist. see retatrutide vs tirzepatide.
what does it cost?
around $120 per 10 mg vial across vetted vendors, but check /compound/retatrutide for live pricing. a full high-dose run is many vials, so budget accordingly.
further reading
- Retatrutide compound overview
- Retatrutide vs tirzepatide
- Retatrutide vs semaglutide
- Ultimate shred stack: retatrutide + tesamorelin protocol
- Tirzepatide-to-retatrutide switch protocol
- GLP-1 plateau breakthrough protocol
- How to read a peptide COA
- Vendor scorecard
- Reconstitution calculator
*Research use only. Not FDA-approved. Not medical advice. Consult a licensed clinician before making any decisions about compounds discussed here. Source: Jastreboff AM et al., NEJM 2023 PMID: 37366315, DOI.*
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