Subcutaneous Injection Technique | Investigational (Phase 3)
How to Inject Retatrutide
This guide walks through the physical retatrutide injection technique: drawing your dose, prepping the skin, setting the angle, injecting, and disposing of the needle. It assumes you have already mixed your vial. If you have not, start with the how to reconstitute retatrutide guide first. For zone anatomy and rotation maps, see the approved retatrutide injection sites page. Retatrutide (LY3437943) is an investigational triple-agonist; this is education, not a substitute for prescriber guidance.
Key Takeaways
- Subcutaneous, once weekly: Retatrutide is injected under the skin one day a week (Coskun 2022; Jastreboff 2023).
- Three approved sites: Abdomen, thigh, or upper arm, rotated with every dose to prevent lipohypertrophy.
- Angle varies: Insert at 45 to 90 degrees depending on needle length and how much fat you have at the site.
- New needle every time: Use a fresh needle for each injection and never recap a used one.
- Dispose immediately: Drop used sharps straight into a puncture-resistant container, never household trash.
Once weekly
Injection Frequency
45 to 90°
Needle Insertion Angle
3 sites
Approved Injection Zones
Investigational compound: Retatrutide (LY3437943) has not received FDA approval as of June 2026. Phase 3 trials are ongoing. The technique steps here are drawn from the published trial literature (Coskun 2022; Jastreboff 2023) and established subcutaneous injection standards (MSKCC). There is no FDA-approved retatrutide label; always follow your prescriber's instructions and the package insert that comes with your medication.
Before You Inject: What You Need
Lay everything out before you start so you are not fumbling with a needle in hand. Retatrutide appears in one of two formats: a lyophilized vial that is reconstituted and drawn with a syringe, which is the format unlawful sellers supply, or Lilly's own product, used in its clinical trials and expanded access program, which comes as a pen device in Lilly's clinical program. This guide leads with the vial-and-syringe format. This section does not cover mixing. If your vial is not yet reconstituted, follow the how to reconstitute retatrutide guide before continuing.
Vial and Syringe Format
- A reconstituted retatrutide vial (already mixed with bacteriostatic water)
- A U-100 insulin syringe (0.5 mL or 1 mL) with a fine-gauge needle
- Alcohol swabs
- A puncture-resistant sharps container
- Optional: gauze or a cotton ball for after the injection
Pen Format
- The retatrutide pen device (clinical-program or future approved pen)
- A new needle for each injection (standard practice for any injector pen)
- Alcohol swabs
- A puncture-resistant sharps container
One note on needles: Eli Lilly has not publicly released a specific needle gauge for the investigational retatrutide pen, so do not anchor on a gauge number you read on a vendor blog. For vial users, a standard U-100 insulin syringe with a fine-gauge needle is appropriate for subcutaneous dosing.
Know Your Dose Before You Draw
The free retatrutide pharmacokinetic calculator converts your reconstitution concentration into the exact volume to draw. No signup.
Open Retatrutide CalculatorStep-by-Step: How to Inject Retatrutide
The sequence below works for both formats; only the dose-loading step splits between vial and pen users. Read it through once before your first attempt, then keep it open beside you for the first few weeks.
- Wash your hands. Soap and water for at least 20 seconds, then dry them. Clean hands are the cheapest infection control you have.
- Inspect the solution. Hold the vial or pen up to the light. Reconstituted retatrutide should look clear and colorless to slightly yellow. Do not use it if it is cloudy, discolored, or has particles floating in it.
- Let it reach room temperature. Injecting cold solution stings more. If your vial was refrigerated, give it a short while on the counter before you draw, but do not heat it.
- Select and clean the site. Pick an approved zone (abdomen, thigh, or upper arm) that you did not use last week. Wipe it with an alcohol swab and let it air dry for 10 to 15 seconds. Do not fan or blow on it.
- Vial users, draw the dose. Attach the needle, pull the plunger back to your prescribed volume, push the needle through the vial stopper, and inject that volume of air in. Invert the vial and withdraw your dose. Tap out air bubbles and gently expel them until the liquid sits at your target marking.
- Pen users, set the dose. Attach a fresh needle and dial to your prescribed volume per the device's own instructions. Prime the pen if its instructions call for it.
- Pinch the skin if needed. Gently lift a fold of skin to pull the fatty layer away from the muscle underneath. This helps if you have limited fat at the site or are using a longer needle. Where there is plenty of subcutaneous fat, the pinch is optional.
- Insert and inject. Push the needle in at 45 to 90 degrees (more on angle below), then press the plunger or button slowly and steadily. Hold for 5 to 10 seconds after the plunger bottoms out so the full dose delivers.
- Withdraw the needle. Pull straight out at the same angle you went in. Press lightly with gauze or a cotton ball if there is a drop of blood. Do not rub the site.
- Dispose immediately. Drop the used needle straight into your sharps container. Never recap it, and never put a loose needle in the trash.
Injection Angle Guidance
Angle depends on needle length versus how deep your subcutaneous fat runs. The goal is to land the drug in the fat layer, not the muscle below it. Shorter insulin needles (around 4 to 6 mm) usually go in at 90 degrees in most adults because the needle simply is not long enough to reach muscle. Leaner people, or anyone using a longer needle, may angle down to 45 degrees to stay in the subcutaneous layer. Lilly has not published a needle gauge for the investigational retatrutide pen, so this angle guidance follows standard subcutaneous practice (MSKCC) rather than a device-specific instruction.
Site Rotation Schedule
Standard subcutaneous practice is to rotate injection sites each week. Repeated injection into the same spot causes lipohypertrophy, a thickened patch of fibrous fat that absorbs medication erratically and undermines a careful titration. Because retatrutide is dosed once weekly and titrated every four weeks, a simple four-week rotation cycle lines up neatly with the schedule and keeps any single spot from being reused too often.
You do not need a complicated map. Move to a fresh zone or a fresh quadrant each week, and avoid any skin that is tender, bruised, or scarred. For the full rotation diagram and the anatomy of each zone, see the approved retatrutide injection sites guide, which covers the four-week cycle in detail.
What to Expect After Injecting
A little local reaction is normal. Mild local reactions such as redness, itching, or a small bruise at the injection site are common with subcutaneous GLP-1 injections and usually settle within a day or two. None of that means you did something wrong.
What you are watching for over time is lipohypertrophy: a firm, rubbery area that builds up under the skin where the same spot has been used too often. It feels different from a passing bruise, and consistent rotation is what prevents it. If you can feel one forming, stop injecting there and let it recover.
Call your prescriber if you get swelling that will not resolve, a spreading rash, or any sign of an allergic reaction such as difficulty breathing. For the full picture on local and systemic effects, see the retatrutide side effects guide.
Sharps Disposal
Drop every used needle straight into a puncture-resistant sharps container. Never recap a used needle and never toss loose needles into household trash or recycling. When the container reaches about three-quarters full, seal it and follow your local rules. Many pharmacies accept sealed sharps containers, and mail-back and household-hazardous-waste programs are widely available. For how to store retatrutide between injections, see the how to store retatrutide guide.
Pen vs. Vial: Technique Differences
The FDA states retatrutide cannot be used in compounding under federal law, so compounding pharmacies cannot lawfully supply it; in the US, lawful access is limited to a clinical trial or Lilly's expanded access program (ClinicalTrials.gov NCT07629401), which a doctor must request, for adults with a BMI of 35 or more whose obesity has not responded to the highest available dose of current weight-loss treatment, who have two or more serious obesity-related complications, and who cannot join a trial. The pen format exists in Lilly's clinical program and is the likely delivery device for an approved product later on. The technique overlaps heavily; the main difference is how you load the dose.
| Step | Vial + Syringe | Pen |
|---|---|---|
| Dose loading | Draw manually from the reconstituted vial | Dial to the prescribed volume |
| Needle | U-100 insulin syringe, fine gauge | Attach a new needle per injection |
| Priming | Inject air equal to dose volume before drawing | Prime per device instructions |
| Angle | 45 to 90 degrees by tissue depth | Typically 90 degrees per device instructions |
For pen-specific detail, see the retatrutide pen page. Do not assume a gauge or cartridge spec that Lilly has not publicly released.
Video Demonstration
Subcutaneous injection technique is the same across GLP-1 class drugs, so a demonstration filmed for semaglutide or tirzepatide applies directly to retatrutide. The walkthrough below covers the full sequence: site selection, angle, preparation, and delivery. Pair it with the approved retatrutide injection sites guide for which zones to use.
GLP-1 subcutaneous injection technique demonstration. The same sequence applies to retatrutide pen and vial administration.
How to Inject Retatrutide: Frequently Asked Questions
Where is best to inject retatrutide?
The three standard subcutaneous GLP-1 sites are the abdomen, thigh, or upper arm. Most people start with the abdomen because the zone is large and easy to reach. Rotate the site with every weekly injection to prevent lipohypertrophy. For zone anatomy, see our injection sites guide.
How do I inject retatrutide at home?
Gather your reconstituted vial or pen, a U-100 insulin syringe, alcohol swabs, and a sharps container. Clean the site and let it dry 10 to 15 seconds, draw your dose, pinch the skin if needed, insert the needle at 45 to 90 degrees, inject slowly, withdraw, and dispose of the needle immediately.
What angle do you inject retatrutide?
Subcutaneous injections go in at 45 to 90 degrees depending on needle length and tissue depth. Shorter insulin needles (4 to 6 mm) typically use 90 degrees in most adults. Leaner people using longer needles may use 45 degrees to stay in the subcutaneous layer and avoid hitting muscle.
How do I inject retatrutide with an insulin syringe?
Draw your prescribed volume into a U-100 insulin syringe from your reconstituted vial. Clean the site, let it dry, pinch the skin, insert at 45 to 90 degrees, push the plunger slowly, hold 5 to 10 seconds, withdraw, and dispose in a sharps container. See the reconstitution guide for mixing steps.
How do I inject the retatrutide pen?
The retatrutide pen used in Lilly's clinical program needs a new needle per injection. Set the dose dial to the prescribed volume, choose an approved site, clean with alcohol, insert at 90 degrees, press the button, and hold for several seconds before withdrawing. Always follow the specific instructions that come with the device.
What time of day should I inject retatrutide?
There is no established required time of day for retatrutide; like other once-weekly GLP-1 injections it can generally be taken with or without food. Pick a consistent day and time each week and follow your prescriber's instructions. Some people prefer evening injections to sleep through the first hours of any nausea, but that is personal preference.
How do I dispose of used retatrutide needles?
Place used needles immediately into a puncture-resistant sharps container. Never recap and never put loose needles in trash or recycling. When the container is three-quarters full, follow local disposal rules. Many pharmacies accept sealed sharps containers, and mail-back programs are available.
What does a normal injection site reaction look like?
Minor local reactions, such as mild redness, itching, or a small bruise, are common with subcutaneous GLP-1 injections and usually settle within a day or two. Consistent rotation prevents the firmer, more persistent reactions tied to lipohypertrophy. Persistent swelling, a spreading rash, or breathing difficulty warrants contacting your prescriber.
Track Your Retatrutide Doses. Free.
Log doses, rotate injection sites, and visualize drug levels with the free retatrutide pharmacokinetic calculator. No signup required.
References
- Memorial Sloan Kettering Cancer Center. How to Give Yourself a Subcutaneous Injection Using a Prefilled Syringe. Patient Education. Available at: mskcc.org. Source for general subcutaneous technique: pinch, insertion angle, withdrawal, and sharps disposal.
- Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple GIP, GLP-1 and glucagon receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept. Cell Metabolism. 2022;34(9):1234-1247.e9. doi:10.1016/j.cmet.2022.07.013. Source for the subcutaneous route, the half-life of approximately 6 days, and the once-weekly dosing rationale.
- Jastreboff AM, Kaplan LM, Frias JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. New England Journal of Medicine. 2023;389(6):514-526. doi:10.1056/NEJMoa2301972. Source for the once-weekly subcutaneous route used across the Phase 2 dose arms.
- U.S. Food and Drug Administration. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. Content current as of 10/01/2026. fda.gov. Source for the statement that retatrutide cannot be used in compounding under federal law.
Medical Disclaimer
This article is for educational purposes only and does not constitute medical advice. Retatrutide (LY3437943) is an investigational compound that has not been approved by the FDA as of June 2026. Phase 3 trials are ongoing and this information may change. Do not start, stop, or change your dose or injection technique without guidance from a licensed clinician. The technique here is drawn from published trial literature and standard subcutaneous injection references; always defer to your prescriber and the package insert that comes with your medication. Clinical trial results represent group averages and individual results vary.
Related Articles
How to Reconstitute Retatrutide
Mixing BAC water and converting your dose to units before you inject.
Retatrutide Injection Sites
Approved zones, the four-week rotation cycle, and which skin to avoid.
Retatrutide Dosing Guide
Titration schedule and dose steps for LY3437943.
Retatrutide Side Effects
Local and systemic effects, with management guidance.