§01what it is

a once-weekly injectable peptide that activates three hunger / metabolism receptors at once. one more than tirzepatide, two more than semaglutide.

the three receptors

• GLP-1 — the classic. slows gastric emptying ~30-40%, signals fullness, lowers blood glucose.
• GIP — improves insulin sensitivity, helps fat metabolism. tirzepatide hits this too.
• Glucagon — the new one. raises resting energy expenditure (burns more), promotes lipolysis, taps fat stores. this is what makes reta different and also why it has unique side effects (heart rate, dysesthesia).

vs tirzepatide (zepbound / mounjaro)

tirz = GLP-1 + GIP. reta = GLP-1 + GIP + glucagon. that third one boosts metabolic burn rather than just suppressing appetite, which is why reta can hit higher weight loss numbers but also nudges heart rate and causes more nausea at peak doses.

FDA status

not approved. eli lilly's TRIUMPH-1 phase 3 obesity trial read out positive in may 2026 (4mg, 9mg, 12mg all hit endpoints). TRIUMPH-5 is a head-to-head vs tirzepatide, finishing dec 2026. submission expected late 2026, approval likely 2027. until then, the only way to access it outside trials is gray-market research peptides.

§02efficacy

in the headline trials, retatrutide at the top dose hits weight loss numbers that approach bariatric surgery.

phase 2 (jastreboff 2023) showed 24.2% weight loss at 12mg / 48 weeks, with no plateau. phase 3 TRIUMPH-1 (may 2026) confirmed 28.3% at 80 weeks and 30.3% at 104 weeks. ~70 lbs on average at the top dose.

timeline for results

• weeks 1-4 — titration. appetite suppression starts. minimal scale movement, mostly water/inflammation.
• weeks 4-12 — real weight loss begins as you step up doses. 1-2 lbs/week common.
• months 4-6 — the curve steepens. people who plateaued on tirz often start moving again.
• year 1+ — kept losing through 80 weeks in trials, no plateau observed.

§03side effects

mostly GI, mostly during titration, mostly tolerable. but reta has two quirks tirz doesn't: faster heart rate and skin dysesthesia.

head-to-head at top doses

the unique ones

dysesthesia — weird skin sensations (tingling, prickling, altered touch). 20.9% at 12mg in phase 3. thought to come from the glucagon receptor activity on peripheral nerves. usually mild but unsettling if you don't expect it.

elevated heart rate — averaged +6.7 bpm at 12mg in phase 2, peaked around week 24, drifted back down toward baseline by weeks 36-48. glucagon raises resting energy use, which raises HR. if you already have a high resting HR or any cardiac issue, this matters.

standard GLP-1 risks

same warnings as zepbound: rare pancreatitis, gallbladder issues, possible thyroid C-cell tumor risk (boxed warning class-wide), low blood sugar if combined with insulin/sulfonylureas. don't use if personal/family history of medullary thyroid carcinoma or MEN2.

§04dosing protocol

no approved schedule yet. the clinical trial titration is the closest thing to a blueprint.

standard trial titration (phase 2, NEJM)

conservative / "gentle start" version

some clinicians (and the everest regenerative protocol, which is what a lot of gray-market users actually follow) start lower because 2mg of reta is roughly equivalent to 5mg+ of tirz given its potency:

• weeks 1-4: 0.5 mg
• weeks 5-8: 1.0 mg
• weeks 9-12: 2.0 mg
• then step up by ~50-100% every 4 weeks based on tolerance up to your target dose

if you've been on tirz at 5mg already, starting reta at 1-2mg is reasonable. if you're new to GLP-1s, start at 0.5mg.

ground rules

• once weekly, same day each week, subcutaneous (belly, thigh, or upper arm).
• rotate injection sites week to week.
• don't escalate faster than every 4 weeks. holding longer is fine, going faster doubles side effects.
• if a dose makes you miserable, drop back to the previous one until symptoms settle, then re-try.
• max studied in obesity trials = 12mg/week. higher exists in other studies but isn't the headline protocol.

§05reconstitution

peptide ships as a dry powder. you add bacteriostatic water to dissolve it, then draw doses with an insulin syringe.

the math (why it matters)

concentration = mg of peptide ÷ mL of BAC water added. once you set that, every "unit" on a U-100 insulin syringe equals 0.01 mL of liquid. so the dose in mg = units × (mg/mL) × 0.01.

step-by-step

1. let the vial reach room temperature. wash hands. clean work surface.
2. swab both vial stoppers (peptide + BAC water) with alcohol pads.
3. draw your chosen volume of BAC water into a reconstitution syringe (a 3mL syringe with an 18-21g needle works well).
4. insert needle into the side of the peptide vial, tilt and slowly trickle the water down the inner wall — don't spray directly onto the powder cake.
5. remove syringe. gently swirl or roll the vial between palms until clear. never shake. shaking foams and damages the peptide.
6. liquid should be completely clear, colorless to faintly yellow. if cloudy or particles, don't use.
7. label the vial with date reconstituted and concentration (mg/mL).

drawing a dose

1. swab vial stopper. flip vial upside down.
2. with an insulin syringe (29-31g, 0.3 or 0.5 mL), pull back to your target units (use the calculator).
3. tap out air bubbles, push them back in, redraw to exact units.
4. swab injection site (belly is easiest — 2 inches from belly button), pinch skin, insert at 90°, push slowly.

storage after reconstitution

• refrigerate at 36-46°F (2-8°C). don't freeze.
• stable for 4-6 weeks reconstituted with BAC water (the benzyl alcohol is what makes "bacteriostatic" work).
• if you used plain sterile water instead of BAC, use within 24 hours. don't do this. just use BAC.
• let the vial warm in your hand for a minute before injecting — cold injections sting more.

§06dosing calculator

enter your vial, your water, your dose. get exact units to draw on a U-100 insulin syringe.

concentration cheat sheet

for a 24 mg vial (peptide.partners standard size):

§07supplies

aside from the peptide itself, the kit is cheap and you can order most of it on amazon.

the easy route — one starter kit

or piece it together

budget: ~$35 if you grab the starter kit, ~$40-60 if you piece it together. lasts months.

§08vendors

all of these sell "for research use only" — the legal fiction that lets the gray market exist. quality varies a lot. the rule is: never buy without a third-party COA (certificate of analysis).

what to actually look for

• third-party COA for your specific batch/lot number, not just a stock COA from years ago.
• HPLC purity ≥98%, ideally 99%+.
• mass spec confirmation of identity (reta is a 39-AA peptide with non-natural substitutions — easy to substitute with cheaper analogs).
• vendor responds to questions about sourcing/manufacturer.
• ships in proper packaging — ice pack, sealed insulated mailer. lyophilized powder is more stable than liquid but heat still degrades it.
• cross-check on reddit's r/Peptides and finnrick rankings.

§09pricing comparison

at high doses, gray-market reta is roughly 5-15× cheaper per month than ro zepbound. that's the whole reason people consider it.

ro body zepbound (current)

gray-market retatrutide (peptide.partners)

12mg vial = $120. 24mg vial = $230 (better $/mg). using the 24mg vial as the base = ~$9.58/mg.

+ ~$35 one-time for the starter kit (or ~$40-60 piecemeal).

the takeaway

at every dose below 12mg, peptide.partners reta is meaningfully cheaper than ro zepbound. at low doses (0.5-2mg) it's 4-15× cheaper. only at the max 12mg dose does it match ro's $449 tier.

§∞bottom line for you

1. if you haven't tried tirz at 7.5mg+ for 8+ weeks, that's the cheap experiment first. dose probably matters more than drug.
2. if you do switch, start at 0.5-1mg weekly given you've been on a low tirz dose. titrate up every 4 weeks.
3. peptide.partners + 24mg vial + 2.4mL BAC water = clean math (10 units = 1mg).
4. expect more nausea and a faster heart rate than tirz, plus possible weird skin sensations. these usually fade.
5. get a recent COA before ordering. if vendor can't produce one for your lot, walk.
6. set a baseline: weight, resting HR, blood pressure. recheck monthly.