Retatrutide

• Week 1-2: Start 2 mg; users report less appetite, some nausea
• Week 2-4: Still 2 mg; levels build, so effects can grow
• Week 4-8: Step up to 4 mg at week 5; slow down if nausea is strong
• Week 8-12: Reach the 5 mg target dose at week 9
• Side effects: Mostly stomach upset; get help for severe belly pain or dehydration

More on each stage

Week 1-2

You start at 2 mg (6.5 units), the starting dose used in the trials. Users commonly report less appetite early on. Nausea, burping, and bathroom changes are most likely now and after each dose increase.

Week 2-4

Still on 2 mg. Retatrutide has a half-life of about 6 days: half of each shot is still in your blood 6 days later. So levels keep building for about 4 weeks (4 to 5 half-lives) before they level off. Effects can grow even though the dose has not changed.

Week 4-8

Step up to 4 mg (13.5 units) at week 5. In the Phase 2 trial, stomach side effects happened mainly during the weeks when doses were being raised. If nausea is still strong, stay on the lower dose longer before stepping up.

Week 8-12

At week 9 you reach the 5 mg target dose (16.5 units), the store dose. For scale: in a 12-week trial in type 2 diabetes, the group stepped up to 12 mg lost about 9 kg more than placebo. In Phase 2, weight loss on 4 mg averaged 12.9% by week 24 and 17.1% by week 48.

Side effects

Mostly stomach upset (nausea, diarrhea, constipation, vomiting) that is worst after starting or raising the dose, plus a faster pulse and, in some people, tingling or sore skin. Get help for severe belly pain, or if you cannot keep fluids down.

Based on what people report in the community sources below. Results vary, and many responses are anecdotal.

• Large weight loss

  Clinical trial

  In a 48-week Phase 2 trial of 338 adults, weight fell by an average of 17.1% on 4 mg and 24.2% on 12 mg, against 2.1% on placebo. In the Phase 3 TRIUMPH-1 trial (2,339 adults, 80 weeks), the company reports 19.0% on 4 mg and 28.3% on 12 mg, against 2.2% on placebo.178

• Less liver fat

  Clinical trial

  In people with fatty liver, liver fat fell by 57% on 4 mg and 81-82% on 8-12 mg after 24 weeks. Liver fat was back in the normal range for 52% of people on 4 mg and 86% on 12 mg; none on placebo.5

• Lower blood sugar in type 2 diabetes

  Clinical trial

  In a 24-week Phase 2 trial of people with type 2 diabetes, HbA1c (a 3-month blood-sugar average) fell by 2.02 points on 12 mg and 1.39 points on 4 mg (after starting at 2 mg), against 0.01 on placebo.4

• Better heart-risk blood tests

  Clinical trial

  In the Phase 2 obesity trial, non-HDL cholesterol fell by up to 26.9%, ApoB (a count of artery-clogging particles) by up to 24.2%, and the inflammation marker hs-CRP by 54.8%, compared with placebo.6

• Lower blood pressure

  Clinical trial

  In the TRIUMPH-4 trial, systolic blood pressure (the top number) fell by 14.0 mm Hg on the highest dose. The company also reports lower systolic blood pressure in TRIUMPH-1.107

• Less knee arthritis pain

  Clinical trial

  In the TRIUMPH-4 trial of 445 adults with obesity and knee arthritis, the company reports average weight loss of 28.7% on 12 mg at 68 weeks. Knee pain scores fell 4.5 points on average, against 2.4 on placebo.10

• Quieter appetite

  Community report

  Users commonly report much less appetite, especially while raising the dose. These are self-reports.17

What it has been studied for

• Obesity or overweight without diabetes (Phase 2: 338 adults for 48 weeks; Phase 3 TRIUMPH-1: 2,339 adults for 80 weeks)1713Clinical trial
• Type 2 diabetes with obesity or overweight (Phase 2; Phase 3 TRIUMPH-2 reported weight loss of 12.7-20.8% at 80 weeks, against 4.0% on placebo)49Clinical trial
• Fatty liver disease (MASLD) in people with obesity (98-person substudy)5Clinical trial
• Knee arthritis in people with obesity (TRIUMPH-4, 445 adults, 68 weeks)10Clinical trial
• Severe obesity with heart disease (TRIUMPH-3: 21.6-22.6% weight loss at 80 weeks)9Clinical trial
• Appetite control and steady weight loss on research-grade product17Community report

Retatrutide (Lilly's code name LY3437943) is a lab-made peptide. It turns on three hormone locks at once. Two of them normally respond to hormones from your gut. Tirzepatide also turns on these two, and in animals they cut how much is eaten. The third lock (for the hormone glucagon) makes the body burn more energy. In lab tests, retatrutide acts most strongly on one of the gut-hormone locks. One shot a week is enough because it leaves the blood slowly: about half of each dose is still there 6 days later.

Peak

Not stated in the published study summaries. They say only that its blood levels suit one shot a week.

Half-life

About 6 days, measured in a 12-week trial in people with type 2 diabetes. That means about half of a dose is gone 6 days after the shot, not all of it; the rest clears over the following weeks. This is why one shot a week is enough. Blood levels rise in step with the dose.

Cleared

Not measured directly. With a 6-day half-life, about 97% would be gone roughly 30 days (4-5 weeks) after your last shot; this uses the usual rule of about 5 half-lives and is an estimate. By the same rule, steady blood levels take about 4 weeks to build after you start or change the dose. After a single shot in the first human study, weight stayed lower for up to 43 days.

Half-life is how long it takes the body to remove half of a dose.2316

Once a week. Any time of day, with or without food. Pick one day and keep it, such as every Sunday. Every 7 days, with no break. Units are for a 60 mg vial mixed with 2 mL water (30 mg per mL).

Step-up plan

When	Dose	Units
Weeks 1-4 (start low) Start here	2 mg	6.5 units, which gives 1.95 mg
Weeks 5-8	4 mg	13.5 units, which gives 4.05 mg
Week 9 onward (store dose)	5 mg	16.5 units, which gives 4.95 mg

• Lower end · conservative slow-titration start

  0.5-4 mg once weekly

  A conservative-start protocol some use to assess tolerance, escalating more slowly than the clinical schedule.17

• Most common · trial-mirror escalation

  1-12 mg once weekly, escalating every 4 weeks

  The community mirrors the Phase 2 trial escalation (1 → 2 → 4 → 8 → 12 mg), chasing the ~24% weight loss reported at 48 weeks — but from research-grade product of unverified potency.17

• Higher end · maintenance settling point

  4-8 mg once weekly (maintenance)

  Where some community members settle for maintenance — enough appetite suppression without pushing to the 12 mg maximum.17

• Trial-mirror step-up (most popular)

  1-12 mg once a week for 48+ weeks, raised every 4 weeks (1, 2, then 4 mg, then up to 8 or 12 mg). The wiki calls this the Phase 2 schedule, but the Phase 2 trial actually started at 2 mg or 4 mg, not 1 mg.171

• Conservative start

  Start at 0.5 mg once a week and climb more slowly than the trials, staying within 0.5-4 mg, for 12-24 weeks.17

• Maintenance

  4-8 mg once a week, ongoing. Users report solid weight loss without going to 12 mg, and say lower doses may mean fewer stomach side effects.17

Research protocols

• Phase 3 TRIUMPH-1 trial (the most current schedule)

  Start at 2 mg once a week and step up every 4 weeks. 4 mg group: 2 then 4 mg. 9 mg group: 2, 4, 6, then 9 mg. 12 mg group: 2, 4, 6, 9, then 12 mg. Treatment ran 80 weeks without breaks.78

• Phase 2 obesity trial

  1, 4, 8, or 12 mg once a week for 48 weeks. The 4 mg and 8 mg groups started at either 2 mg or 4 mg; the 12 mg group started at 2 mg. Doses were raised every 4 weeks. Starting at 2 mg instead of 4 mg reduced stomach side effects.15

• Phase 1b trial in type 2 diabetes

  0.5 to 12 mg once a week for 12 weeks. The highest doses were reached in steps: 3 then 6 mg, or 3, 6, 9, then 12 mg.2

• Store plan

  The store plan's target dose is 5 mg once a week, taken continuously. Like the trials, it starts low and steps up every 4 weeks: 2 mg, then 4 mg at week 5, then 5 mg at week 9. 5 mg sits between the 4 mg and 6 mg trial steps.71

Retatrutide is investigational — not FDA-approved, only available through Phase 3 trials or unverified research-grade vendors. The glucagon-receptor component raises heart-rate and metabolic-monitoring concerns the community cannot self-manage. Community reports cannot verify product authenticity.

Dosing guidance built from the cited research and community reports. It is not a prescription.

On

Ongoing, with no set end date

Break

No routine break

Why the break helps

Unlike most peptides, retatrutide is not cycled. In the weekly-dose trials, people took it every week with no planned breaks for the whole study, which lasted from 12 weeks (the first diabetes trial) to 80 weeks (TRIUMPH-1, 2, and 3). Some TRIUMPH-1 volunteers kept going to 104 weeks. Stopping tends to undo the result: with tirzepatide, a closely related drug, people switched to placebo after 36 weeks saw their weight rise 14.0% over the next 52 weeks, while those who stayed on lost another 5.5%. Stop or pause only for a reason, such as side effects, pregnancy plans, or surgery, and plan it with a doctor.

Common

• Nausea. In TRIUMPH-1 it affected 28.6% of people on 4 mg and 42.4% on 12 mg, against 14.8% on placebo. It is worst after starting or raising the dose.

  What to do Eat smaller meals, stop when you feel full, and go easy on greasy food. Do not raise the dose until it settles. If it stays strong, go back to the last dose that felt fine.

• Diarrhea, constipation, or vomiting. In TRIUMPH-1, diarrhea affected 25-34% of people, constipation 24-26%, and vomiting 11-25%, depending on dose.

  What to do Drink plenty of fluids. If you cannot keep fluids down for a day, see the dehydration warning below.

• Tingling, burning, or skin that hurts to touch (doctors call this dysesthesia). In TRIUMPH-1 it affected 5.1% on 4 mg and 12.5% on 12 mg, against 0.9% on placebo, and was mostly mild to moderate. It was more common in TRIUMPH-4 (20.9% on 12 mg).

  What to do Tell your doctor. Staying on a lower dose may help; stop if it is bothering you.

• Faster resting heart rate. In the Phase 2 obesity trial the rise grew with dose, peaked at week 24, and then eased. Some users also report feeling warmer.

  What to do Check your resting pulse now and then. If it stays well above your usual, or you feel pounding or skipped beats, stop and see a doctor.

• Redness, itching, or a small bump where you injected

  What to do Rotate sites and use a fresh syringe every time. If redness spreads or gets hot and painful, see a doctor.

Stop and get help

• Pancreatitis (inflamed pancreas): severe belly pain that does not go away, sometimes spreading to the back, with or without vomiting. It has been seen with related drugs.

  What to do Stop retatrutide and go to an emergency room.

• Gallbladder problems: pain in the upper right belly, fever, or yellow skin or eyes. Related drugs raise the risk.

  What to do Stop and see a doctor the same day.

• Dehydration that can harm the kidneys: vomiting or diarrhea where you cannot keep fluids down, peeing much less, or feeling dizzy.

  What to do Stop and get medical care the same day. Kidney injury has been reported with related drugs.

• Racing or irregular heartbeat, chest pain, or fainting

  What to do Call 911 (or your local emergency number).

• Allergic reaction: hives, swelling of the face, lips, or throat, or trouble breathing

  What to do Stop retatrutide and call 911 (or your local emergency number) right away.

• Changes in your vision, especially if you have diabetes. Related drugs warn that a fast drop in blood sugar can briefly worsen diabetic eye damage (retinopathy).

  What to do See your doctor or an eye doctor promptly.

• A lump in the neck, hoarseness that will not go away, or trouble swallowing. Related drugs caused thyroid tumors in rats; whether this happens in people is unknown.

  What to do Stop and see a doctor.

Do not use if

• You are pregnant, trying to get pregnant, or breastfeeding. The trials excluded pregnancy, and the label for tirzepatide, a related drug, says it may harm an unborn baby.
• You or a parent, brother, sister, or child have had medullary thyroid cancer or MEN2 (multiple endocrine neoplasia type 2).
• You have ever had pancreatitis, or you have gallbladder disease that causes symptoms.
• You have type 1 diabetes, or severe gastroparesis (a stomach that empties very slowly).
• You have diabetic retinopathy (eye damage from diabetes), unless an eye doctor is checking it. The tirzepatide label warns that a fast drop in blood sugar can briefly make it worse; get an eye exam before you start and keep up regular checks.
• You have serious kidney disease, uncontrolled high blood pressure, or had a heart attack, stroke, or heart-failure hospital stay in the last 3 months. These people were kept out of the trials.
• You have had major depression or another serious mental illness in the last 2 years (also kept out of the trials).
• You are under 18.

Storage

Keep it

Keep the mixed vial in the fridge (2-8 °C), in its box, away from light and heat. Do not freeze it: the label for tirzepatide, a related drug, says never to freeze it or use it after freezing. Never leave it in a hot car.

How long

Use within 90 days of mixing. A mixed vial kept in the fridge holds its strength for 60-90 days, then slowly starts to lose potency. Wipe the rubber top with an alcohol swab before every draw.

Drawing your dose

Syringe: a 0.3 mL (30-unit) U-100 insulin syringe with half-unit marks, so small doses are easy to read. Doses above 30 units (up to 40 here) need a 0.5 mL (50-unit) syringe.

1. With this mix, every 1 unit line on a U-100 insulin syringe holds 0.3 mg. Your doses fall between lines, so draw to the closest mark: 6.5 units for 2 mg (gives 1.95 mg), 13.5 units for 4 mg (gives 4.05 mg), and 16.5 units for the 5 mg target dose (gives 4.95 mg).
2. Wipe the top before every draw. Hold the syringe at eye level, flick out air bubbles, and push the plunger back to the exact line.
3. Pinch a fold of skin, insert the needle at 45 to 90 degrees, push slowly, and wait a few seconds before pulling out.
4. Missed a shot? Retatrutide has no published rule. The FDA label for tirzepatide, a related weekly shot, says: take it within 4 days (96 hours) of the missed day; if more than 4 days have passed, skip it and take the next one on your usual day.
5. Look before you draw. Do not use the vial if the liquid is cloudy, changes colour, or has specks in it.
6. Use a new sterile syringe every time and never share one.

• Tesamorelin

  Tesamorelin aims at deep belly (visceral) fat by a different route: it raises your own growth hormone. In a trial of people with HIV, visceral fat fell 10.9% over 6 months, against 0.6% on placebo. Retatrutide drives overall weight loss. Both are in the store's Lean Machine stack; they have not been tested together.18

• Ipamorelin

  Ipamorelin is also in the store's Lean Machine stack. Users report deeper sleep, often within the first 1-2 weeks, and better recovery from exercise (self-reports). In pigs, it released growth hormone without the rise in stress hormones (ACTH and cortisol) that two older, similar peptides caused (animal study).2019

Interactions

• Other GLP-1 drugs: semaglutide (Ozempic, Wegovy), tirzepatide (Mounjaro, Zepbound), liraglutide, dulaglutide

  They act on the same receptors, so side effects stack up. No study has tested them together, and community users generally avoid stacking them.

  What to do Do not combine. If you are switching from one of these, ask a doctor how to switch and what dose to start on.

• Insulin or diabetes pills that push insulin out (sulfonylureas such as glipizide or glyburide)

  Low blood sugar. Related drugs carry this warning when used with these medicines.

  What to do Talk to your doctor first; your diabetes dose may need lowering. Learn the signs of low blood sugar (shaky, sweaty, confused) and keep juice or glucose tablets nearby.

• Birth-control pills

  Slower stomach emptying can make pills work less well. The tirzepatide label warns about this, especially after the first dose and each dose increase.

  What to do Switch to a non-pill method, or add condoms, for 4 weeks after starting and for 4 weeks after each dose increase (the rule on the tirzepatide label).

• Surgery, colonoscopy, or anything needing anesthesia or deep sedation

  Food can stay in the stomach even after fasting, which raises the risk of breathing it into the lungs. This has been reported rarely with related drugs.

  What to do Tell the doctor doing the procedure that you take retatrutide, well before the day.

• Warfarin and other pills where small changes in blood level matter

  Slower stomach emptying can change how these pills are absorbed.

  What to do Ask your doctor; they may want extra blood tests when you start or change the dose.

Videos

• Retatrutide Deep Dive: Newest Weight-Loss Peptide vs Semaglutide & TirzepatideDr. Michael Moeller · 2025
• I Tried Retatrutide – Here's What HappenedNick Norwitz MD PhD · 2026
• Retatrutide: The 24% Weight Loss Drug — GI Doctor Explains

Sources

1. 1Jastreboff et al., NEJM 2023 (Phase 2 obesity trial, 338 adults, 48 weeks)Clinical trial
2. 2Urva et al., Lancet 2022 (Phase 1b trial in type 2 diabetes: dose steps, half-life, weight)Clinical trial
3. 3Coskun et al., Cell Metab 2022 (discovery, mouse studies, and first single-dose human study)Study
4. 4Rosenstock et al., Lancet 2023 (Phase 2 trial in type 2 diabetes)Clinical trial
5. 5Sanyal et al., Nat Med 2024 (Phase 2 fatty-liver substudy)Clinical trial
6. 6Ruotolo et al., Diabetes Obes Metab 2026 (Phase 2 heart-risk blood markers)Study
7. 7Eli Lilly press release, May 21 2026: TRIUMPH-1 Phase 3 topline results (via BioSpace)Clinical trial
8. 8HCPLive, May 21 2026: TRIUMPH-1 weight loss and side-effect ratesReference
9. 9HCPLive, July 23 2026: TRIUMPH-2 and TRIUMPH-3 results and FDA filing planReference
10. 10Pharmaceutical Journal, Dec 2025: TRIUMPH-4 knee arthritis resultsReference
11. 11Kaczynski et al., Biomedicines 2026 (review; dysesthesia rates across retatrutide trials)Review
12. 12ClinicalTrials.gov NCT04881760 (Phase 2 obesity trial: who was excluded)Clinical trial
13. 13ClinicalTrials.gov NCT05929066 (TRIUMPH-1: who was excluded)Clinical trial
14. 14FDA label for Zepbound (tirzepatide), a related drug: warnings, missed doses, birth control, storageDrug label
15. 15Aronne et al., JAMA 2024 (SURMOUNT-4: weight regain after stopping tirzepatide)Clinical trial
16. 16Certara: Understanding steady-state pharmacokinetics (4-5 half-life rule)Reference
17. 17Peptide Protocol Wiki: Retatrutide community protocols (100 reports)Community
18. 18Falutz et al., J Acquir Immune Defic Syndr 2010 (tesamorelin belly-fat trial)Clinical trial
19. 19Raun et al., Eur J Endocrinol 1998 (ipamorelin, first selective growth-hormone secretagogue; rats and pigs)Study
20. 20Peptide Protocol Wiki: Ipamorelin community protocols (200 reports; sleep and recovery self-reports)Community

Where people discuss it

• r/Peptides (subreddit)
• Peptide Protocol Wiki — Retatrutide community (100 reports)

Some peptides, like semaglutide (Ozempic and Wegovy), are FDA-approved medicines. Most of the peptides people research are not. That label sounds like the FDA tested something and turned it down. Usually it means something else: nobody has paid for the studies the FDA needs to see. Here is why.

The FDA doesn’t test drugs. Companies do.

The FDA does not run its own drug tests. A company that wants to sell a new medicine has to test it first, and pay for it. It studies the drug in animals, then in people: first 20 to 100 volunteers, then a few hundred, then up to 3,000. Then it sends all the results to the FDA. FDA scientists review them and decide whether the benefits outweigh the risks.

So approval always starts with a company asking for it. If no company applies, the FDA has nothing to review, however promising the research looks.

Those studies cost about a billion dollars

A study in the medical journal JAMA estimated that bringing one new drug to market costs a typical company about $1.1 billion. That figure includes the money spent on drug ideas that failed along the way, because many drugs that start human testing never make it.

A patent is how a company earns that money back

A patent is a right the government gives an inventor. For up to 20 years from the day the inventor applies, nobody else may make or sell the invention without permission.

For a drug company, that right is what makes the billion-dollar bet worth it. While the patent lasts, the company is the only seller, so it can charge enough to pay back the studies and the failures. When the patent runs out, other companies can sell cheap copies, called generics, and the price drops.

The FDA adds a shorter shield of its own. For 5 years after a brand-new drug is approved, no copycat version can apply for approval. That helps, but it is much shorter than a patent can last.

Why most peptides can’t be patented

To get a patent, an invention has to be new, and it has to be something people made, not something found in nature. Most popular peptides fail one test or both.

They come from nature. Many are copies or small pieces of molecules your body already makes. KPV is a 3-building-block piece of the hormone that tans your skin. BPC-157 is copied from a protein in stomach juice. In 2013 the US Supreme Court ruled that something that exists in nature, like a human gene, cannot be patented just because someone found it and pulled it out.

They aren’t new anymore. Many were first described in research papers decades ago. Scientists were already testing KPV in the 1980s. Once something has been published, it no longer counts as new, so nobody can patent it now, and any patents from back then have long since run out.

Without a patent, a company that paid for the studies would soon face rivals selling the same peptide without having paid for any research. Few companies will spend a billion dollars on a product anyone can copy. So nobody goes first, and the large human studies never happen.

The workaround: change the molecule

Drug companies do make peptide medicines, but they change the peptide first. A changed molecule is a new invention, so it can be patented. Semaglutide is a lab-made version of GLP-1, a gut hormone your body releases after meals, changed so one shot lasts a week. Tesamorelin (Egrifta) is the body’s own growth-hormone signal with a small fatty chain added. Both went through the full studies, and both are FDA-approved.

The natural versions, and the many peptides nobody has changed and patented, stay where they are: studied in labs and animals, used by the biohacking community, and never put through large human trials.

What this means for you

When a peptide is “not FDA-approved,” it usually means no company has paid for the large human studies. It does not mean the FDA tested it and found it harmful.

It also does not mean it is proven safe or proven to work. Without those studies, nobody knows the best dose for sure, or what rare or long-term side effects it may have. And the FDA does not check research peptides for purity or strength the way it checks approved medicines. That is why this page labels every finding by the kind of study behind it, and lists who should not use it.

Sources for this section

1. 1FDA: How drugs are developed and approved (the FDA does not test drugs; companies submit the evidence)
2. 2FDA: The drug development process, step 3: clinical research (study sizes for each phase)
3. 3Wouters, McKee & Luyten, JAMA 2020, corrected 2022: median cost to bring a new drug to market, $1.14 billion
4. 4US patent law, 35 U.S.C. § 154: a patent lasts 20 years from the filing date
5. 5FDA: Frequently asked questions on patents and exclusivity (5-year new chemical entity exclusivity)
6. 6US Supreme Court, Association for Molecular Pathology v. Myriad Genetics (2013): naturally occurring genes cannot be patented