Retatrutide: research

An experimental weekly injection with phase 3 weight-loss results.

Also called: LY3437943, LY-3437943, Reta.

GLP-1 / GIP / glucagon agonists · GIP, GLP-1 and glucagon receptor triple agonist.

40 primary human records: 34 registered studies, including one exercise study, four case or observational reports, and two social-media studies. The 40 include ongoing studies and studies without results.

Studies

Retatrutide dosage

Typical reported dose: 2 mg once a week to start, up to 12 mg

  • Phase 1 single dose: 0.1 mg: 0.1 mg once, on study day 1 once only, under the skin. Studied in a trial. Studied in: Healthy adults in the first-in-human study. (source)
  • Phase 1 single dose: 0.3 mg: 0.3 mg once, on study day 1 once only, under the skin. Studied in a trial. Studied in: Healthy adults in the first-in-human study. (source)
  • Phase 1 single dose: 1 mg: 1 mg once, on study day 1 once only, under the skin. Studied in a trial. Studied in: Healthy adults in the first-in-human study. (source)
  • Phase 1 single dose: 3 mg: 3 mg once, on study day 1 once only, under the skin. Studied in a trial. Studied in: Healthy adults in the first-in-human study. (source)
  • Phase 1 single dose: 4.5 mg: 4.5 mg once, on study day 1 once only, under the skin. Studied in a trial. Studied in: Healthy adults in the first-in-human study. (source)
  • Phase 1 single dose: 6 mg: 6 mg once, on study day 1 once only, under the skin. Studied in a trial. Studied in: Healthy adults in the first-in-human study. (source)

Highest studied: Highest repeated dose studied: 12 mg under the skin once weekly..

These are doses reported in labels, trials or user reports, not a personal plan. Check the source behind each one.

Work out syringe units with the dosing calculator

Retatrutide side effects and risks

Reported side effects

  • Nausea: TRANSCEND T2D 1: 16%, 20%, 26% at 4/9/12 mg versus 4% placebo. Phase 2 obesity registry, non serious nausea: 28/62 at 12 mg versus 8/70 placebo., moderate. Talk to a clinician if nausea persists or is severe. Do not increase the dose while symptoms continue. (source)
  • Diarrhea: TRANSCEND T2D 1: 19%, 26%, 23% at 4/9/12 mg versus 4%. TRIUMPH 2: 27%, 34%, 34% versus 13%., moderate. Drink fluids if you can. Get help if you are dehydrated or cannot drink. (source)
  • Vomiting: TRANSCEND T2D 1: 16%, 15%, 18% at 4/9/12 mg versus 2%., moderate. Repeated vomiting or very little urine needs urgent care. (source)
  • Constipation: TRANSCEND T2D 1: 4%, 8%, 7% at 4/9/12 mg versus 1%. Some phase 2 groups exceeded 10%; at 12 mg, 10/62 versus 2/70. Rates varied by trial., moderate. Discuss fluids and fiber with a clinician. Severe pain, vomiting or inability to pass gas needs urgent care. (source)
  • Sensitive skin, burning or tingling: TRANSCEND T2D 1: 4%, 2%, 4% at 4/9/12 mg versus 0%, with three severe cases. TRIUMPH 2: 4%, 6%, 7% versus 1%., moderate. Report skin symptoms that persist, spread or hurt. A rash with trouble breathing is an emergency. (source)
  • Fatigue: TRANSCEND T2D 1: 1%, 6%, 7% at 4/9/12 mg versus 3%., mild. Check food intake, hydration and blood sugar as needed. (source)
  • Injection-site reactions: TRANSCEND T2D 1: 1%, 2%, 1% at 4/9/12 mg versus 1%., mild. Spreading redness, fever or a painful swollen area needs an infection check. (source)
  • Low blood sugar: The monotherapy trial: glucose <54 mg/dL in 0, 2 (2%), 1 (1%) at 4/9/12 mg versus 0 placebo; no severe episodes. Related tirzepatide warns of added risk with insulin or sulfonylureas; retatrutide combination risk is unknown., serious. Check blood sugar and follow your rescue plan. Confusion, seizures or low blood sugar that does not resolve needs emergency help. (source)
  • Low blood pressure or faintness: TRIUMPH 2: 1%, 5%, 6% at 4/9/12 mg versus <1% placebo., moderate. Review hydration and blood-pressure medicines. Fainting needs urgent care. (source)
  • Faster heart rate or palpitations: Phase 2 obesity: average heart rate rises increased with dose and peaked at week 24. The paper reported average changes, not the share of people affected., moderate. Check resting heart rate. Get a persistent rise reviewed; chest pain or fainting needs urgent care. (source)
  • Abnormal heart rhythm or electrical signals: TRANSCEND T2D 1: 4/134 (3%), 2/133 (2%), 1/136 (1%) at 4/9/12 mg versus 0/134. These small numbers cannot establish the cause or a reliable risk estimate., serious. Get a new, sustained racing or irregular heartbeat checked promptly. (source)
  • Gallstones: TRANSCEND T2D 1: 0, 1 (1%), 3 (2%) at 4/9/12 mg versus 0 placebo., serious. Upper-right belly pain, fever or yellow skin or eyes needs urgent care. (source)
  • Pancreatitis: Related tirzepatide carries this warning. Retatrutide trial plans listed pancreatitis as a reason to stop; its frequency remains unknown., serious. Stop further doses and get urgent care for severe belly pain that persists, especially if it spreads to your back. (source)
  • Dehydration and sudden kidney injury: Related tirzepatide warns of dehydration related kidney injury. One unverified exposure case also involved infection and missed insulin, so retatrutide's role is unclear., serious. Get urgent care if you cannot keep fluids down, have very little urine or feel very dizzy. (source)

Stop and get help if

  • Severe belly pain that persists, especially spreading to the back, with or without vomiting: Stop further doses and get urgent care for possible pancreatitis.
  • Face, tongue or throat swelling, trouble breathing, collapse, or widespread hives with dizziness: Call emergency services now.
  • Chest pain, fainting, or a sustained racing or irregular heartbeat: Get emergency care now, especially with shortness of breath or weakness.
  • Repeated vomiting, unable to keep fluids down, very little urine, confusion or severe dizziness: Get urgent care for dehydration, salt imbalance or kidney problems. Keep the vial and packaging for the care team.
  • Low blood sugar that does not resolve, confusion, seizures or loss of consciousness: Follow your blood sugar rescue plan and get emergency help if symptoms persist. Never give food or drink to an unconscious person.
  • Sudden vision loss or a major new vision change: Get urgent eye care or emergency care.
  • Yellow eyes or skin, dark urine, easy bruising or severe upper-right belly pain: Stop further doses and get urgent care for possible liver or gallbladder injury.
  • Severe belly swelling or pain, vomiting, and unable to pass stool or gas: Get urgent care for a possible severe stomach or bowel problem.
  • Type 1 diabetes with vomiting, high blood sugar or raised ketones: Follow your sick-day plan and get urgent diabetes care. Do not stop basal insulin without your diabetes team.

Who should avoid it

  • pregnant: Pregnancy: avoid use. Human safety is unknown; trial plans listed pregnancy as a reason to stop treatment.
  • breastfeeding: Breastfeeding: avoid use. The obesity trial excluded breastfeeding; effects on milk and the baby are unknown.
  • tryingToConceive: Trying to conceive: avoid use and discuss past doses with your clinician. Retatrutide's waiting period before pregnancy is unknown.
  • under18: Under 18: safety and an effective dose are unknown. Completed studies of benefit were in adults.
  • mtcOrMen2: Personal or family medullary thyroid cancer or MEN2: avoid use, following precautions for related GLP-1 drugs. Human thyroid-cancer risk with retatrutide is unknown.
  • eatingDisorderHistory: Eating-disorder history: appetite loss, eating too little and rapid weight loss can worsen the disorder. Discuss this with your care team.
  • pancreatitisHistory: Past pancreatitis: talk to your clinician first; key trials excluded this group. Severe belly pain that persists needs urgent care.
  • gallbladderDisease: Gallbladder disease: discuss it with your clinician. Rapid weight loss can raise gallstone risk; gallstones occurred in the phase 3 diabetes study.
  • gastroparesis: Slow stomach emptying: retatrutide can make it slower. Talk to your clinician before further doses if you have severe gastroparesis or ongoing vomiting.
  • diabeticRetinopathy: Diabetic eye disease: tirzepatide's label warns of brief worsening with rapid blood sugar improvement. Retatrutide's monotherapy trial excluded disease needing treatment; arrange eye checks.
  • kidneyDisease: Kidney disease: vomiting and diarrhea can cause dehydration and sudden kidney injury. A dose-adjustment rule has not been established.
  • liverDisease: Liver disease: discuss advanced scarring or cirrhosis with your clinician. Unverified products have been linked to sudden liver injury.
  • heartCondition: Heart disease: talk to your clinician first. Trials found faster heart rates and a few abnormal rhythms or electrical signals; long-term heart safety and benefit remain unknown.
  • uncontrolledBloodPressure: Uncontrolled blood pressure: get it checked first. Weight loss or dehydration can also lower pressure, so your medicines may need review.
  • diabetes: Diabetes: review medicines and blood sugar checks with your care team. Do not replace insulin; type 1 diabetes and missed insulin raise the risk of ketone buildup.
  • surgeryPlanned: Planned surgery: tell the anesthesia team about your last dose. Related GLP-1 drugs can let stomach contents enter the lungs; retatrutide's safe stopping interval is unknown.
  • activeCancer: Active cancer: talk to your oncologist first; safety is unknown. Trials could stop treatment if cancer developed.
  • psychiatricCondition: Mental health condition: discuss major mood or eating changes with your care team. Severe illness was excluded from the phase 3 monotherapy trial; a drug-related risk is unproven.
  • testedAthlete: Tested athlete: ask your anti-doping body for a ruling. Australia says retatrutide is not listed for 2026, while WADA S0 covers unapproved drugs; contamination can also cause a violation.
  • other: Past serious allergy to retatrutide or an injection ingredient: avoid further doses.
  • other: Underweight or unable to eat enough: avoid weight-loss regimens. Trials stopped treatment at very low BMI and allowed changes for poor nutrition.

Interactions

  • Insulin: Tirzepatide's label warns of low blood sugar with insulin. Ask your diabetes team to review doses, especially if eating less. Never stop basal insulin in type 1 diabetes.
  • Sulfonylureas and meglitinides: These drugs can cause low blood sugar without food. Tirzepatide's label warns of added risk; its size with retatrutide is unknown.
  • Other GLP-1 or GIP/GLP-1 medicines: Combining these drugs may worsen stomach upset and poor intake. Human retatrutide combination trials are lacking; tirzepatide's label advises against combining it with GLP-1 drugs.
  • Amylin drugs, including experimental versions: Both may reduce appetite and slow stomach emptying. Retatrutide plus cagrilintide has been studied in animals; human results are lacking.
  • DPP-4 inhibitors: The monotherapy trial excluded these drugs. Ask your prescriber to review overlap; added benefit and safety are unknown.
  • Oral hormonal contraceptives: Slower stomach emptying may affect pill absorption. Discuss contraception and vomiting/diarrhea; tirzepatide’s 4-week backup rule is unproven for retatrutide.
  • Warfarin and drugs that need precise blood levels: Slower stomach emptying or poor intake may affect these medicines. Ask about blood-clotting tests called INR, or drug-level checks. The retatrutide interaction study has no posted results.
  • Other oral blood thinners: Vomiting or poor intake may disrupt blood-thinner dosing. Contact your prescriber if you may not have absorbed a dose; direct retatrutide interaction results are lacking.
  • SGLT2 inhibitors: Used together in the phase 3 diabetes trial. Make a sick-day plan for severe illness, poor intake or dehydration; a direct drug interaction is unproven.
  • Blood-pressure medicines and diuretics: Weight loss and fluid loss can lower blood pressure. Check dizziness and hydration; ask your prescriber to review medicines if symptoms occur.

Product quality risks

  • Three Australian vials labelled 10 mg contained 5.13, 19.0 and 16.5 mg. Finding the right molecule did not ensure the right dose; this small sample cannot show how common mislabelling is.
  • After severe vomiting and a tear in the food pipe, TGA tested a purported retatrutide product. It had no retatrutide, but unlisted semaglutide at about eight times TGA-assessed levels.
  • Victoria reported six sudden liver-injury cases linked to purported retatrutide by June 19, 2026. Contamination was suspected but unproven.
  • Unregulated injections may contain the wrong drug, too much or too little drug, microbes or bacterial toxins called endotoxin.
  • Counterfeit pens and research-only labels do not establish medicine-quality manufacture or lawful sale for human use.

How Retatrutide works

It acts on three hormone signals that control hunger, blood sugar and how the body uses fuel. GLP-1 also slows stomach emptying. Animal studies suggest glucagon increases energy use; the size of this effect in people is unknown.

  • GLP-1 receptor: Helps you feel full, releases insulin when blood sugar rises and can slow stomach emptying.
  • GIP receptor: Helps release insulin when blood sugar rises and contributes to effects on blood sugar and fuel use.
  • Glucagon receptor: Changes how the liver uses fuel. Animal studies show increased energy use.

Half-life: About 6 days in early human studies. Blood tests can detect it for much longer.

Gaps: No approved label, retail product or independent clinician dosing guideline was found. Several completed drug-level, organ-impairment and interaction studies have no available results. Their doses, dose increases and dose-adjustment rules remain unknown. TRIUMPH-3 and TRIUMPH-4 have sponsor announcements. Full published papers or registry results were not found, so sponsor-only outcome numbers are omitted. TRIUMPH-1 full safety tables, group sizes and selected-extension details were not checked in full. One PubMed/NEJM sleep-apnea hybrid result appears to lack a minus sign. Only the clear intention-to-treat values are included. TRIUMPH-1 counts differ: 2339 in the paper versus 2335 in the registry. TRIUMPH-3 sponsor and registry counts also differ; these have not been reconciled. Long-term heart and kidney outcomes, lifetime exposure, rare cancers and rare severe harms remain unknown. Blood-test changes and early reviews cannot answer these questions. There are too few data on pregnancy, breastfeeding or children. The time to stop before conception and the backup interval for birth-control pills are unknown. No controlled human trials were found combining retatrutide with tirzepatide, semaglutide, cagrilintide, drugs that raise growth hormone or injury-recovery peptides. A rat cagrilintide-combination study cannot establish effects or safety in people. How common community practices are is unknown. Frequency labels describe this search; nMentions counts only explicitly counted reports, not all users. Daily microdosing, split dosing, planned cycles, receptor-reset breaks and 14–16 mg weekly lack controlled human evidence. The highest verified repeated trial dose is 12 mg under the skin weekly. Storage, mixing concentration, compatibility and shelf life in bacteriostatic water are unknown for unregulated vials. General 28-day advice does not establish potency or sterility. No specific WADA ruling was found to resolve Australia’s 2026 not-listed statement against S0. Athletes need confirmation from their anti-doping body. FDA nomination details and a retatrutide-specific PCAC vote were not verified. FDA explicitly says retatrutide cannot be compounded. No named entry was found in the October 2026 Australian Poisons Standard. Coverage by broader drug groups and local laws remains unresolved. News reports mention US poison-center cases and possible deaths. Retatrutide-specific datasets and medical records were unavailable; rates and causes remain unconfirmed. Secondary analyses and reviews reuse primary trials. They are not counted as new, independent trials. Seven registered trials have published primary outcome papers, from first human dosing through phase 3. Expanded access is a separate record, not a trial. Large trial effects apply to selected participants. Rare harms, long-term outcomes and community schedules remain uncertain. The three-vial analysis did not report sterility or endotoxin results, or demonstrate toxic metal exposure. Testing can reduce uncertainty, but cannot make an unapproved product approved or guarantee its safety. A home dose-increase rule and a personal maximum dose have not been established. Compounding category 1/2/3 placement and withdrawn-nomination details were not verified. The July 2026 PCAC meeting about other peptides did not authorize retatrutide. Expanded access under NCT07629401 does not authorize routine retail sale or compounding. FDA warnings address retatrutide marketing and compounding. No approved retail prescription product exists. Possession and import rules vary by location. A missing named Australian schedule entry does not permit supply or import of an unapproved medicine. Semaglutide or tirzepatide monitoring status does not establish retatrutide’s anti-doping status. Unverified products may also contain banned contaminants.

Related to Retatrutide

Retatrutide: the short version

Sources

Sources checked: 2026-10-22.

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