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№ 003

Retatrutide

Triple agonist (GLP-1 + GIP + glucagon) from Eli Lilly. In trials it outperforms Tirzepatide for weight loss.

Fat Loss
Evidence: Moderate

Retatrutide: Triple agonist (GLP-1 + GIP + glucagon) from Eli Lilly. In trials it outperforms Tirzepatide for weight loss. Retatrutide is the newest weight-loss compound in development at Eli Lilly.

FDA ⓘ
Not approved
WADA
Not banned
Typical dose
Start 2mg sub-q weekly
Half-life ⓘ
~6 days
Route ⓘ
Subcutaneous
Schedule
Once weekly
In plain English

Retatrutide is the newest weight-loss compound in development at Eli Lilly. It's a stronger cousin of Tirzepatide (Mounjaro / Zepbound) and pulls bigger weight loss in trials, often 20%+ of body weight. One injection per week. Side effects are real, especially in the first few weeks.

Status & legalityWhat do these mean? →
Natty? ⓘ
Not natty
FDA ⓘ
Not approved

Investigational. In Phase 3 trials with Eli Lilly. Not yet approved.

Compounding ⓘ
Investigational

In clinical trials, not yet approved for prescription.

WADA ⓘ
Not listed

GLP-1/GIP/glucagon agonists are not on the WADA Prohibited List (semaglutide and tirzepatide sit on the 2026 Monitoring Program only). As an unapproved investigational substance, retatrutide could still be argued under S0 (non-approved substances) for tested athletes, so treat it as risky if you compete.

Prescribed ⓘ

Not yet available by prescription. Trial-only access through Lilly's clinical program.

Before you start

Wear a CGM the first 14 days.

Triple-agonist response varies, measure to know. A two-week sensor (~$80, OTC, no prescription) tells you more about how YOUR body is responding to Retatrutide than any protocol guide can. Most users wear one and don't again. The first cycle is the one that matters.

Get a CGM →

Who it's for

  • →People plateaued on Tirzepatide
  • →Users targeting >15% body weight loss
  • →Metabolic-syndrome adults under provider guidance

What to expect

  1. Week 1

    Appetite drops sharply. Nausea common days 2-4.

  2. Week 4

    First titration step. ~3-6lb down for most users.

  3. Week 8

    Steady-state approaching. Cumulative loss 6-12lb depending on dose.

Looking at Retatrutide? Your next 3 steps

  1. 1Work out your syringe units

    Vial size + BAC water turns into the exact units to draw for Retatrutide.

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  2. 2See what to stack & monitor

    The companion supplements and the bloodwork worth tracking on this kind of protocol.

    Bloodwork guide →
  3. 3Save it & ask the Coach

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How it works (mechanism)

Triple agonist, GLP-1, GIP, and glucagon receptors all activated by one molecule. The glucagon arm adds metabolic-rate elevation (mild thermogenesis) on top of the appetite suppression, driving the largest trial weight-loss effect to date.

Dosing protocol

Members only

Stacks well with

Members only

Stack essentials

Members only

Side effects

01Nausea (especially first 2 weeks of each titration step)
02Constipation or diarrhea
03Fatigue / lethargy
04Reduced HRV in some users
05Underrating protein intake from low appetite

When NOT to use

  • ⚠History of medullary thyroid carcinoma or MEN-2
  • ⚠Pancreatitis history
  • ⚠Pregnancy / nursing

Bloodwork to monitor

  • • Lipid panel
  • • Liver enzymes (ALT/AST baseline + every 3 mo)
  • • A1C if metabolic context

Common mistakes

  • • Titrating too fast, stick to 4-week steps
  • • Not eating enough protein during the cut (lean mass loss)
  • • Stopping abruptly with no maintenance plan (rebound common)

Drug & supplement interactions

  • ⚠Same class warnings as Tirzepatide: insulin dose reduction, gastric-emptying delays, contraceptive absorption
  • ⚠Glucagon arm may slightly elevate heart rate, caution with stimulants

The Pepdex take

Pepdex take: 4mg weekly is the typical maintenance dose. Nausea profile is rougher than Tirzepatide for the first 2-3 weeks, eases by week 3 in most users. Splitting the weekly dose into two half-doses doesn't help, it just spikes side effects on each split, no smoother on either. The trial data on Reta is the strongest in the GLP class. Pre-FDA, so source quality matters more here than with approved alternatives.

Community patterns

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New to Retatrutide? Grab the starter checklist.

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AI Coach, live sample
Members only
is 250mcg of bpc enough for a knee injury?
For a knee, 250 mcg sub-q daily is the standard working dose and a solid place to start. The trick with BPC is consistency, give it weeks, not days. Inject close to the joint, run it 4-6 weeks, and don't drop below 200 mcg, it tends to stop cracking the threshold reliably down there. If it hasn't moved at all by week 3, that's when adding TB-500 earns its place.
how much bac water for a 10mg reta vial?
3 mL is the standard play for a 10 mg reta vial. That's 3,333 mcg/mL, clean unit math across the titration: 2 mg = 60 units, 4 mg = 120 units, 6 mg = 180 units on a 100-unit insulin syringe. Run 2 mL instead if you want fewer, more concentrated shots (5,000 mcg/mL, so 2 mg = 40 units). Since most people titrate up over ~12 weeks, 3 mL keeps the numbers cleanest.
what should i track on bloodwork for tirzepatide?
Lipid panel, ALT/AST (liver enzymes), and an A1C, baseline before you start then every 3 months. If you've got metabolic-syndrome history, add fasting glucose and insulin so you can actually watch insulin sensitivity improve. You don't need a big hormone panel for a GLP-1.

Ask the Coach anything about Retatrutide or your own stack. This is it working.

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Frequently asked

What is Retatrutide?+
Retatrutide is the newest weight-loss compound in development at Eli Lilly. It's a stronger cousin of Tirzepatide (Mounjaro / Zepbound) and pulls bigger weight loss in trials, often 20%+ of body weight. One injection per week. Side effects are real, especially in the first few weeks.
Is Retatrutide FDA approved?+
Investigational. In Phase 3 trials with Eli Lilly. Not yet approved.
Is Retatrutide legal?+
Retatrutide is not FDA-approved. It is sold by compounding pharmacies (with a prescription) and as "research only" by peptide vendors. Possession is generally not criminalized but distribution without authorization may be. Verify local laws.
Is Retatrutide banned by WADA?+
Retatrutide is not currently on the WADA prohibited list. GLP-1/GIP/glucagon agonists are not on the WADA Prohibited List (semaglutide and tirzepatide sit on the 2026 Monitoring Program only). As an unapproved investigational substance, retatrutide could still be argued under S0 (non-approved substances) for tested athletes, so treat it as risky if you compete.
Are you still natty after taking Retatrutide?+
No. Retatrutide is a performance-enhancing peptide and would disqualify a strict natty claim.
Do doctors prescribe Retatrutide?+
Not yet available by prescription. Trial-only access through Lilly's clinical program.
What's the typical dose of Retatrutide?+
Dosing depends on your goal, experience, and tolerance. The full Retatrutide protocol (dose, frequency, and how to titrate) is in the members section on the entry page.
What are the side effects of Retatrutide?+
Common side effects include: Nausea (especially first 2 weeks of each titration step); Constipation or diarrhea; Fatigue / lethargy; Reduced HRV in some users. Less common effects and full safety details are on the entry page.
How long until Retatrutide starts working?+
Appetite drops sharply. Nausea common days 2-4.
What can you stack with Retatrutide?+
Retatrutide is commonly combined with complementary compounds. The full stacking protocol (what to pair, dosing, and timing) is in the members section on the entry page.
Where do people get Retatrutide?+
Pepdex does not sell, ship, or recommend suppliers. Retatrutide is not FDA-approved; prescription versions require licensed clinical care, and "research only" markets carry real legal and quality risks. /coa explains how to verify a Certificate of Analysis and /guides/scam-vendor-spotting covers the red flags.
Retatrutide vs Mazdutide, which is better?+
How Mazdutide and Retatrutide compare on research category, evidence tier, regulatory status, and reported side effects. Full head-to-head comparison: https://pepdex.co/compare/mazdutide-vs-retatrutide
Retatrutide vs Cagrilintide, which is better?+
How Cagrilintide and Retatrutide compare on research category, evidence tier, regulatory status, and reported side effects. Full head-to-head comparison: https://pepdex.co/compare/cagrilintide-vs-retatrutide
Retatrutide vs Tirzepatide, which is better?+
Retatrutide vs Tirzepatide: head to head on weight-loss potential, mechanism, side effect profile, and current availability. Full head-to-head comparison: https://pepdex.co/compare/retatrutide-vs-tirzepatide

Head-to-head with Retatrutide

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Retatrutide vs Mazdutide →
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Retatrutide vs Cagrilintide →
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Retatrutide vs Tirzepatide →
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Retatrutide vs Semaglutide →
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Tirzepatide

Strong weight loss with a cleaner side effect profile than semaglutide. A dual agonist (GLP-1 + GIP), FDA-approved as Mounjaro / Zepbound.

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Semaglutide

The original weight-loss wave, sold as Ozempic / Wegovy. A GLP-1 agonist.

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Liraglutide (Saxenda / Victoza)

Daily GLP-1 receptor agonist. FDA-approved 2010 (Victoza, T2D) and 2014 (Saxenda, obesity). The first wave of modern GLP-1 weight-loss therapy and direct predecessor to Semaglutide.

№ 023
Cagrilintide

An appetite-control shot for weight loss. A long-acting amylin agonist that works on a different pathway than the GLP-1 drugs, often paired with Semaglutide as 'CagriSema' to break GLP-1 plateaus.