What is Reta + Cagri Blend?
Reta + Cagri Blend is a fixed combination of two weight-management research compounds in one vial: 25mg retatrutide (LY3437943), a triple agonist at the GLP-1, GIP and glucagon receptors. It is paired with 5mg cagrilintide, a long-acting, lipidated analog of the beta-cell hormone amylin. Together that is 30mg of active compound per vial at a fixed 5:1 ratio.
The principle is the same as with CagriSema, just with a different incretin partner: an incretin agonist and an amylin analog address two different satiety pathways. Retatrutide is by far the more potent part, which is why the blend is built reta-anchored and dosed that way too. Both building blocks have their own lexicon entries with the details of each mechanism.
The vial comes as lyophilised powder that you reconstitute with bacteriostatic water and inject subcutaneously once a week. There are no controlled studies of this exact combination; the evidence comes from the individual compounds and from research on cagrilintide with semaglutide.
This information is for research and educational purposes only. No medical advice.
How it works
Retatrutide activates three receptors at once. Through the GLP-1 receptor it dampens appetite and slows gastric emptying, the GIP component reinforces the metabolic effects. The glucagon component is associated in research with higher energy expenditure and increased fat breakdown in the liver. In the phase 2 trial the higher doses reached up to 24.2 percent weight reduction after 48 weeks (Jastreboff 2023).
Cagrilintide acts elsewhere: amylin is released together with insulin from the beta cells and works via amylin receptors, mainly in the circumventricular organs of the brainstem. There it strengthens satiety after a meal and likewise slows gastric emptying, but through a pathway independent of the incretin receptors. Thanks to its lipidation, cagrilintide stays active long enough for a weekly dose (Lau 2021).
In the blend both signals come together. That is the logic of the incretin-plus-amylin combinations: in the phase 1b trial of cagrilintide plus semaglutide, weight loss after 20 weeks was 17.1 percent versus 9.8 percent with semaglutide alone (Enebo 2021). Whether this carries over to retatrutide as the partner has not been studied. On top of that, the cagri share in the blend is small: at 2.4mg of blend it is 0.4mg of cagrilintide.
What you need
The kit is the same as for retatrutide or cagrilintide on their own:
- The Reta + Cagri Blend vial with the lyophilised powder (30mg, two compounds)
- Bacteriostatic water for reconstitution, 2 or 3ml per vial
- U-100 insulin syringes
- Alcohol swabs for the vial cap and the skin
- A sealable container for used needles
One vial lasts a long time: around twelve weeks at 2.4mg per week, twice that at 1.2mg. So a clean routine when piercing the stopper pays off, it gets used a lot.
Reconstitution
All figures refer to the total amount of both compounds; the 5:1 ratio stays fixed in every dose. With 3ml of bacteriostatic water on 30mg you get 10mg of blend per ml: 0.6mg is then 6 units on the U-100 syringe, 1.2mg is 12 units, 2.4mg is 24 units. With 2ml the solution is 15mg per ml, 2.4mg is then 16 units and 1.2mg is 8 units.
The calculator above works this out for any water volume. 3ml is the more comfortable standard because every step lands on whole units and the solution is less concentrated. 1ml is too coarse for the low steps, 0.6mg would be only 2 units.
Add the water slowly to the vial, then swirl or shake until everything is clearly dissolved, both are fine. The solution is clear to slightly opalescent; if it turns cloudy, gel-like or lumpy, do not use it.
Injection
Inject subcutaneously into the fat layer under the skin, classically the abdomen (keep two finger widths clear around the navel), the front of the thigh or the back of the upper arm. Once a week, ideally on the same weekday, so the level stays even.
- Clean the skin with an alcohol swab and let it dry briefly
- Lift a small fold of skin
- Insert the needle at 45 to 90 degrees
- Inject, slowly or briskly both work, wait a moment, then withdraw the needle
- Put the needle straight into the sharps container
Rotate the injection site from week to week. People who struggle with nausea often inject in the evening so that the peak of nausea falls into sleep.
Use and dosing
What the research shows
There is no study of the retatrutide plus cagrilintide combination, neither preclinical nor in humans. The evidence comes from three directions. For retatrutide there is the phase 2 trial (Jastreboff 2023): up to 24.2 percent weight reduction after 48 weeks in the highest dose group, plus the phase 2a data in MASLD with a marked reduction of liver fat (Sanyal 2024).
For cagrilintide, the phase 2 trial with 706 participants over 26 weeks showed dose-dependent weight reduction in mono application (Lau 2021). The principle of combining an amylin analog with an incretin is best documented for cagrilintide plus semaglutide: 17.1 versus 9.8 percent after 20 weeks in the phase 1b trial (Enebo 2021) and around 22.7 percent after 68 weeks in the phase 3 trial REDEFINE 1.
It does not follow that retatrutide plus cagrilintide works the same way. Retatrutide on its own is already stronger than semaglutide. Whether the small cagri share of the blend adds anything on top is an open question. You find the studies with links in the source block below.
Side effects
Both components are considered generally well tolerated in the trials. The profile of both is shaped by gastrointestinal effects. In combination two satiety signals add up, which amplifies nausea especially at the start. Slow titration therefore matters even more than with the individual compounds.
- Gastrointestinal: nausea, fullness, vomiting, diarrhoea or constipation are the most common observations, clearly dependent on how fast the dose is raised.
- Fluids and nutrients: with food intake strongly reduced, fluid intake often drops too; drink enough and keep an eye on protein.
- Heart rate: mild increases in heart rate are documented for the glucagon component of retatrutide.
- Muscle mass and gallbladder: rapid weight loss takes muscle mass with it and can favour gallbladder problems; resistance training and protein counteract that.
- Fixed ratio: the dose of both components rises and falls together, neither can be reduced on its own.
- Evidence: no clinical studies exist for the combination. Long-term data are missing for retatrutide.
If the solution turns gel-like or lumpy, do not use the vial. Slight cloudiness on its own is not a reason.
Storage
The unreconstituted powder is robust: normal room temperature (around 20 to 25 degrees) is fine, ideally dark and dry. For longer periods it can go in the fridge, but it does not have to.
Once reconstituted, the solution goes in the fridge (2 to 8 degrees) and keeps there for several months; the bacteriostatic water brings a preservative for that. At 2.4mg per week a 30mg vial is empty after around twelve weeks. The solution stays perfectly usable for that long. Do not freeze and do not leave it in the sun.
Swirling or shaking is both fine. Going through the same stopper repeatedly is normal, just wipe the cap each time first.
