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Strong human trialsIn clinical trials

Retatrutide

Also known as: LY3437943 · Reta · GLP-3 · GLP-3 RT

Updated 74 sources

Retatrutide is a once-weekly injected peptide from Lilly that hits three receptors at once: GLP-1, GIP and glucagon. That makes it the first triple agonist in late trials. Phase 3 results put average weight loss in the high 20s percent at the top dose. It is not approved yet, so everything outside a trial is grey market.
Calculate with RetatrutideDosage chart

Quick facts

Half-life
  • About 6 days in the phase 1b trial, with exposure rising in proportion to dose. Built for once-weekly shots.
Routes
  • Subcutaneous injection
Reported dose ranges
  • 0.25 to 12 mg (subcutaneous injection)
Vial sizes
  • 5 mg, 10 mg, 12 mg, 15 mg, 20 mg, 24 mg, 30 mg, 40 mg, 50 mg, 60 mg
FDA status
  • In clinical trials
WADA
  • Not confirmed

What people use Retatrutide for

  • Weight loss, the main use in trials and in the grey market
  • Type 2 diabetes control, studied in TRIUMPH-2 and the TRANSCEND-T2D program
  • Liver fat, knee osteoarthritis pain and sleep apnea, studied as trial outcomes
  • Quieting food noise, as commonly described in community posts
  • Recomposition alongside a high-protein diet
  • Switching from tirzepatide when weight loss stalls

How it is thought to work. One molecule switches on three hormone receptors. GLP-1 cuts appetite and slows stomach emptying. GIP boosts the insulin response. Glucagon raises energy use and liver fat burning. A fatty-acid tail binds albumin in the blood, so one shot lasts about a week. Compared with the natural hormones it is weaker at the glucagon and GLP-1 receptors and much stronger at GIP. Tirzepatide hits two of these receptors; semaglutide hits one.

Retatrutide dosing

18 protocols from studies, guides and community reports, grouped by goal. Tap a source badge to see where a number came from.

Weight loss6

Weight loss, phase 3 trial schedule (TRIUMPH)

Amount
2 to 12 mg
How often
Once weekly. Start at 2 mg, step up every 4 weeks to a target of 4, 9 or 12 mg, then hold.
Route
Subcutaneous injection
Cycle
80 weeks in the trial
Timing and details

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Weight loss, phase 3 step ladder as published by dosing guides

Amount
2 to 12 mg
How often
Once weekly, 4 weeks at each step: 2, 4, 6, 9, then 12 mg and hold
Route
Subcutaneous injection
Titration (5 steps) and details

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Weight loss, phase 2 trial (48 weeks)

Amount
1 to 12 mg
How often
Once weekly. Start at 2 or 4 mg, step up every 4 weeks to 4, 8 or 12 mg.
Route
Subcutaneous injection
Cycle
48 weeks
Timing and details

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Weight loss, common community start

Amount
0.25 to 1 mg
How often
Once weekly, held a few weeks to judge tolerance before stepping up
Route
Subcutaneous injection
Timing and details

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Weight loss, trial-style start (community)

Amount
2 to 4 mg
How often
Once weekly: 2 mg for 4 weeks, then 4 mg
Route
Subcutaneous injection
Titration (2 steps) and details

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Weight loss, small weekly steps (community)

Amount
0.5 to 1.5 mg
How often
Once weekly, raised a little every 1 to 2 weeks
Route
Subcutaneous injection
Timing and details

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Switching from tirzepatide2

Switching from tirzepatide (guide)

Amount
1 to 1.5 mg
How often
Once weekly, starting at about 20 to 30% of the tirzepatide dose (5 mg tirzepatide becomes 1 to 1.5 mg)
Route
Subcutaneous injection
Timing and details

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Switching from tirzepatide (community)

Amount
0.5 to 1 mg
How often
Once weekly, restarting low at 0.5 to 1 mg
Route
Subcutaneous injection
Timing and details

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Other protocols: injected10

Type 2 diabetes, phase 1b trial (12 weeks)

Amount
0.5 to 12 mg
How often
Once weekly. Start between 0.5 and 3 mg, then ladders of 3 to 6 mg or 3, 6, 9 and 12 mg.
Route
Subcutaneous injection
Cycle
12 weeks
Timing and details

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Split dosing, twice weekly (community)

Amount
0.5 to 1 mg
How often
Twice weekly: 0.5 mg for 2 weeks, 0.75 mg for 2 weeks, then 1 mg (2 mg a week total)
Route
Subcutaneous injection
Titration (3 steps) and details

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Split dosing of the weekly total (guide)

Amount
2 mg
How often
Weekly total split into 2 or 3 shots or every 2 to 3 days, e.g. 6 mg a week as 2 mg shots
Route
Subcutaneous injection
Timing and details

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Holding a mid-range dose (community)

Amount
4 to 8 mg
How often
Once weekly, held at the dose that works
Route
Subcutaneous injection
Timing and details

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Restart after a break (community)

Amount
2 to 8 mg
How often
Once weekly: back to 2 mg, then 4, 6 and 8 mg in weekly steps
Route
Subcutaneous injection
Titration (4 steps) and details

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Maintenance taper (community)

Amount
4 to 8 mg
How often
Once weekly, stepping down over about 4 weeks: 8, 6, 5, then 4 mg
Route
Subcutaneous injection
Titration (4 steps) and details

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Low-dose maintenance (community)

Amount
0.5 to 2 mg
How often
Once weekly at 0.5, 1 or 2 mg
Route
Subcutaneous injection
Timing and details

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Maintenance every 2 weeks (community)

Amount
4 mg
How often
Every 2 weeks, e.g. 4 mg
Route
Subcutaneous injection
Timing and details

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Maintenance, twice weekly (guide)

Amount
1 mg
How often
1 mg twice weekly (2 mg a week)
Route
Subcutaneous injection
Timing and details

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General weekly range (guide)

Amount
0.5 to 12 mg
How often
Once weekly
Route
Subcutaneous injection
Timing and details

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Doses shown are what sources report, labelled by origin. Not medical advice.

Full Retatrutide dosage guideEvery titration step in syringe units, missed doses and how to mix.

Vial strengths and syringe units

Every Retatrutide vial size with the water volumes sources use. Units are what to draw on a U-100 insulin syringe, worked out exactly.
Retatrutide: concentration and U-100 syringe units for each vial size and water volume
WaterStrength0.5 mgdose, units1 mgdose, units2 mgdose, units
5 mg vial
1 mLCompetitor guide5 mg/mL100.1 mL200.2 mL400.4 mL
2 mLCompetitor guide2.5 mg/mL200.2 mL400.4 mL800.8 mL
3 mLCompetitor guide1.667 mg/mL300.3 mL600.6 mL1201.2 mL2 draws
10 mg vial
1 mLCompetitor guide10 mg/mL50.05 mL100.1 mL200.2 mL
2 mLCompetitor guide5 mg/mL100.1 mL200.2 mL400.4 mL
3 mLCompetitor guide3.333 mg/mL150.15 mL300.3 mL600.6 mL
20 mg vial
1 mLCompetitor guide20 mg/mL2.50.025 mL50.05 mL100.1 mL
2 mLCompetitor guide10 mg/mL50.05 mL100.1 mL200.2 mL
3 mLCompetitor guide6.667 mg/mL7.50.075 mL150.15 mL300.3 mL
All 10 vial sizes on the dosage chart (7 more)
Units are on a U-100 insulin syringe (100 units = 1 mL). U-50 and U-30 barrels read the same units.Water volumes from

Doses shown are what sources report, labelled by origin. Not medical advice.

Calculate with this peptideYour vial, your water, your dose: Retatrutide in syringe units, with the math shown.

What people report

What Retatrutide users write on Reddit, counted post by post. These are reports, not measured rates or advice.

Community-reportedFrom 900 Reddit posts and comments, last mined Oct 23, 2026r/Retatrutide, r/Peptides, r/Peptidesource, r/PeptideDiscussion

Doses people report for Retatrutide

Weight loss705 mentions

Amounts reported for weight loss, with mention counts
ReportedMentions
2 mg283
1 mg222
4 mg145
0.5 mg108
3 mg91

Goal not stated18 mentions

Amounts reported for goal not stated, with mention counts
ReportedMentions
5 mg4
0.5 mg3
2 mg3
10 mg3
20 mg3

Metabolic health5 mentions

Amounts reported for metabolic health, with mention counts
ReportedMentions
1 mg3
2 mg3

How often

Dosing frequencies reported, with mention counts
ReportedMentions
Once a week281
Twice a week67
Every third day8
Every two weeks5
Three times a week4

Most mentioned alongside

Side effects people mention

  • Nausea49 mentions

    Most common fixes: lower the dose (10), wait for it to resolve over time (3)

  • Fatigue40 mentions

    Most common fix: lower the dose (2)

  • Sleep issues24 mentions

    Most common fix: take magnesium (3)

  • Fast heart rate19 mentions

  • Diarrhea17 mentions

    Most common fix: lower the dose (4)

  • Skin sensitivity17 mentions

    Most common fix: lower the dose (2)

Doses shown are what sources report, labelled by origin. Not medical advice.

Retatrutide side effects

What trials and labels report, kept apart from what users and guides report. Frequencies are worded as each source states them.

Reported in studies and labels6

From clinical trials and regulatory documents.

  • Nausea

    TRIUMPH-1: about 29% at 4 mg, 38.4% at 9 mg and 42.4% at 12 mg, vs 14.8% on placebo

    How people manage it

    • Start low. In phase 2, a 2 mg start caused fewer stomach side effects than a 4 mg start.

  • Diarrhea

    TRIUMPH-1: 25.2% at 4 mg, 34.1% at 9 mg, 32.0% at 12 mg, vs 13.5% on placebo. TRIUMPH-3: 30.1% at 9 mg

  • Constipation

    TRIUMPH-1: 23.8% at 4 mg, 25.9% at 9 mg, 26.1% at 12 mg, vs 10.9% on placebo

  • Vomiting

    TRIUMPH-1: 10.6% at 4 mg, 22.8% at 9 mg, 25.3% at 12 mg, vs 4.8% on placebo

    How people manage it

    • Trials allowed dose cuts when stomach effects were hard to tolerate. Dropping back a step is a normal move.

  • Dysesthesia (skin tingling, burning or sensitivity)

    TRIUMPH-1: 5.1% at 4 mg, 12.3% at 9 mg, 12.5% at 12 mg, vs 0.9% on placebo. TRIUMPH-4: 8.8% at 9 mg, 20.9% at 12 mg. Mostly mild

    How people manage it

    • Mostly mild in trials. A lower dose is the usual lever if it bothers you.

  • Stopping because of side effects

    TRIUMPH-1: 4.1% at 4 mg, 6.5% at 9 mg, 11.2% at 12 mg, vs 4.6% on placebo. TRIUMPH-4: 12.2% at 9 mg, 18.2% at 12 mg, vs 4%

    How people manage it

    • Slower steps and holding a dose that works are the main tools people use to stay on.

Reported by users and guides6

From community reports and dosing guides. Not measured rates.

  • Nausea: guide tips for getting through it

    No separate rate. These are a guide's tips for the trial nausea above

    How people manage it

    • Hold the current dose 2 to 4 extra weeks before stepping up if nausea is rough.

  • Diarrhea: guide tips for getting through it

    No separate rate. These are a guide's tips for the trial diarrhea above

    How people manage it

    • Drink 2 to 3 liters of fluid a day and add electrolytes.

  • Constipation: guide tips for getting through it

    No separate rate. These are a guide's tips for the trial constipation above

    How people manage it

    • Keep fluids up.

  • Vomiting: guide tips for getting through it

    No separate rate. These are a guide's tips for the trial vomiting above

    How people manage it

    • Smaller, protein-first meals.

  • Skin tingling, pins and needles, sunburn-like skin

    A recurring r/Retatrutide topic, reported at doses as low as 1 to 2.5 mg, often 2 to 3 days after a shot or during cardio

    How people manage it

    • Some posters add vitamin B6 or B12. That is a community habit, not something tested.

  • Raised resting heart rate and palpitations

    Commonly reported on r/Retatrutide and a frequent reason posters taper or move back to tirzepatide. An observational grey-market study also linked unapproved use to more cardiovascular symptoms

    How people manage it

    • Posters who are bothered by it taper the dose or switch back to tirzepatide.
All 19 Retatrutide side effects and how people manage themEvery management tip, who should not use it, and side-effect questions.

Storage

Powder (before mixing)

Temperature
2 to 8 °C

Keep the powder in the fridge. Guides give 12 to 24 months as typical. No validated shelf life exists for research vials.

Mixed vial

Temperature
2 to 8 °C
Use within
28 days

Keep the mixed vial in the fridge and use it within about 28 days. Community posts cite 28 to 30 days. People on low weekly doses often ask whether a vial really goes off at a month; nobody has validated a date for research vials.

Mixed with: Bacteriostatic water

Mixing. Run the water down the inside wall of the vial, then swirl gently. Do not shake. At high doses people use a stronger mix, around 10 mg per mL, so one shot fits in a 1 mL syringe. One community poster mixes 20 mg with 3 mL on purpose, to make small dose steps easier to measure.

Stacks people report

Combinations from guides and community posts, with the reason given.
  • Cagrilintide

    Adds amylin, a fullness signal retatrutide does not touch, on the CagriSema model. One guide runs retatrutide 2 then 4 mg first, adds cagrilintide at 0.25 mg in week 9, and climbs to 12 mg plus 2.4 mg. Pre-blends of 12.5 mg retatrutide with 2.5 mg cagrilintide in 2.5 mL exist. No trial has tested this pair.

  • MOTS-c

    Logged alongside retatrutide in community data and sold as stacks. There is no dosing evidence for the pair.

  • Tesamorelin

    Logged alongside retatrutide in community data and sold as stacks. There is no dosing evidence for the pair.

  • GHK-Cu

    Logged alongside retatrutide in community data and sold as stacks. There is no dosing evidence for the pair.

  • SS-31

    Logged alongside retatrutide in community data and sold as stacks. There is no dosing evidence for the pair.

  • BPC-157

    Logged alongside retatrutide in community data and sold as stacks. There is no dosing evidence for the pair.

  • Ipamorelin

    Logged alongside retatrutide in community data and sold as stacks. There is no dosing evidence for the pair.

Compare Retatrutide

Evidence and legal status

Evidence: strong human trials

Phase 1, phase 2 (338 people) and five positive phase 3 trials, including TRIUMPH-1 (2,339 people) published in NEJM on 2026-09-29. Head-to-head trials against tirzepatide and semaglutide are running. Safety beyond about 2 years is unknown, and split dosing, sub-2 mg maintenance and cycling were never tested.

FDA and WADA

In clinical trials

Under FDA-regulated trials; not approved yet.

Not FDA approved. Lilly plans to file for approval in Q1 2027 once its manufacturing package is done. An expanded early access program opened in August 2026 for adults with treatment-resistant obesity and 2 or more serious complications.

The FDA has sent 14 warning letters to retatrutide sellers since December 2024, and a research use only label does not protect a seller. Lilly sued six US sellers in August 2026. By June 2026 the FDA adverse event system held at least 14 reported hospitalizations tied to retatrutide. We found no FDA page confirming its compounding status. WADA's 2026 Monitoring Program names semaglutide and tirzepatide, not retatrutide; how the non-approved substances clause applies is unconfirmed.

WADA: Not confirmed

Retatrutide questions

What is the starting dose of retatrutide?

The trials start at 2 mg once a week. In phase 2, starting at 2 mg instead of 4 mg cut stomach side effects and cost little weight loss. Community users usually start lower: 1 mg weekly is the most common start on r/Retatrutide, and some begin at 0.5 mg.

What is the retatrutide titration schedule?

Steps of 4 weeks. The phase 3 TRIUMPH ladder is reported as 2, 4, 6, 9, then 12 mg weekly, with targets of 4, 9 or 12 mg. Lilly confirms the 2 mg start and the 4-week steps. Many community users stop climbing once a mid-range dose works.

How much bacteriostatic water for a 10 mg retatrutide vial?

1 mL or 2 mL are the most common choices. 1 mL makes 10 mg per mL, which keeps higher doses small enough for one syringe. 2 mL makes 5 mg per mL, which is easier for small early doses. Use the calculator for the exact units.

What is the half-life of retatrutide?

About 6 days, measured in the phase 1b trial. That is why it is dosed once a week. Exposure rises in proportion to dose.

How long does retatrutide stay in your system?

At about 4 to 5 half-lives, roughly 30 days to clear. The same math means each dose step takes about 4 weeks to reach steady state. In phase 1, weight loss after a single dose was still visible on day 43.

How long does retatrutide take to work?

Appetite drops in the first weeks. In phase 2, weight loss at 24 weeks ranged from 7.2% to 17.5% depending on dose. Grey-market users did worse: one observational preprint found 4.7% at 3 months and 7.2% at 12 months, against 15.5% at 12 months in trials.

How do you switch from tirzepatide to retatrutide?

There is no trial guidance. One guide says take retatrutide on your next scheduled day with no washout, at about 20 to 30% of the tirzepatide dose, so 5 mg tirzepatide becomes 1 to 1.5 mg. On r/Retatrutide some switchers wait 1 to 2 weeks and restart at 0.5 to 1 mg.

What maintenance dose do people use on retatrutide?

It has not been studied. Community posters taper down to 0.5 to 2 mg weekly, or keep their dose and stretch it to every 2 weeks. Some report regain after tapering to 1 mg and add a small boost shot when hunger returns. Maintenance is one of the busiest topics on r/Retatrutide.

Why do people split their retatrutide dose?

At low doses like 1 to 1.5 mg, many users say appetite control fades by day 3 or 4 and hunger is back before the next shot. Splitting the weekly amount into two shots, often Monday and Thursday, evens that out. No trial has tested split dosing.

Is retatrutide better than tirzepatide?

On paper it loses more weight. Retatrutide 12 mg gave about 24% at 48 weeks in phase 2 and 28.3% at 80 weeks in TRIUMPH-1. Tirzepatide 15 mg gave 20.9% at 72 weeks in SURMOUNT-1. Those are different trials. The head-to-head trial, TRIUMPH-5, has no results yet.

Is retatrutide FDA approved?

No. Lilly plans to file for approval in Q1 2027. An expanded early access program opened in August 2026 for some adults with hard-to-treat obesity.

What is GLP-3?

Slang for retatrutide. There is no hormone called GLP-3. The name stuck because retatrutide hits a third receptor on top of the two tirzepatide hits.

What is the dysesthesia side effect of retatrutide?

Tingling, burning or extra-sensitive skin. In phase 3 it hit 12.5% of people at 12 mg in TRIUMPH-1 and 20.9% in TRIUMPH-4, and was mostly mild. Community users report it at much lower doses too, often a couple of days after a shot.

Do people cycle retatrutide?

Some do: 16 to 24 weeks on, 4 to 8 weeks off, tapering at the end. That pattern comes from community practice. No trial has tested cycling.

Can you take retatrutide with semaglutide or tirzepatide?

Guides say no. Retatrutide already covers the GLP-1 receptor, so stacking it with another GLP-1 drug doubles up on the same pathway.

Ask about Retatrutide

Answers come from this site's pages only, with a link to each source.

Sources

74 sources, each checked by date. Record updated Oct 23, 2026. Numbers are restated in our own words and labelled by where they came from.

Clinical study14

  1. Preliminary results of retatrutide from TRIUMPH-1Lilly Medical · checked Oct 23, 2026
  2. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 TrialNew England Journal of Medicine · checked Oct 23, 2026
  3. LY3437943, a novel triple agonist, in people with type 2 diabetes: a phase 1b trialThe Lancet · checked Oct 23, 2026

Regulatory7

  1. NCT05929066 (TRIUMPH program)ClinicalTrials.gov · checked Oct 23, 2026
  2. Retatrutide Meets Phase 3 Weight Loss Endpoints in 2 Obesity TrialsHCPLive · checked Oct 23, 2026
  3. Eli Lilly offers new weight loss drug to some patients before FDA approvalFOX6 News · checked Oct 23, 2026

Competitor guide8

  1. Retatrutide peptide pagePeptIQ · checked Oct 23, 2026
  2. Retatrutide ProtocolPeptide Dosing Protocols · checked Oct 23, 2026
  3. Retatrutide 5 mg vial dosage protocolPeptideDosages · checked Oct 23, 2026

Community-reported45

  1. Switching from weekly retatrutide micro-titration to a fixed 4-week scheduler/Retatrutide · checked Oct 23, 2026
  2. Starting dose?r/Retatrutide · checked Oct 23, 2026
  3. Given your height/initial weight, what was your starting dose?r/Retatrutide · checked Oct 23, 2026