You have a vial of retatrutide that's already mixed and ready to use. This guide shows you how to measure the right dose and inject it just under your skin, once a week. No medical background needed.
What retatrutide is, and how it works (in plain English)
Retatrutide is a once-a-week injection that helps you lose weight — and in trials it produced the biggest weight loss of any weight-loss drug so far (around a quarter of body weight at the highest doses). Here's why it works so well, without the jargon.
The big picture: it works on both sides of the scales
Picture your body weight like a bathtub. Water pouring in from the tap = the calories you eat. Water going down the drain = the energy you burn. Most weight-loss drugs only turn down the tap. Retatrutide turns down the tap and opens the drain wider at the same time. That double action is its whole secret.
It does this by copying three natural body hormones at once. (The technical name is a "triple agonist" — "agonist" just means "a switch that turns something on".) Think of it as pressing three buttons together:
🔘 Button 1 — the "I'm full" button
This is the same hormone the famous drugs Ozempic and Wegovy copy. It does two things:
- It turns down your appetite in your brain — you feel full sooner and think about food less. Lots of people describe the constant background chatter about food (the "food noise") going quiet, like someone turned the volume down.
- It slows how fast your stomach empties, so a small meal keeps you full for hours — like a slow-release valve on your stomach.
🔘 Button 2 — the "smooth the ride" button
This one works alongside Button 1. It helps your body deal with blood sugar and — importantly — it calms the nausea that Button 1 can cause. Think of it as a co-pilot who keeps the journey comfortable so you can actually stick with the drug instead of feeling too sick to continue.
🔘 Button 3 — the "furnace" button (the new, special one)
The first two buttons are also in a drug called Mounjaro. Retatrutide adds a third button the others don't have, and it's the reason the weight loss is bigger:
- It turns up your body's idle burn rate — you burn a bit more energy even while just sitting still, like nudging up the thermostat on a furnace. (Some people say they feel slightly warmer.)
- It tells your liver to burn off its own stored fat. In trials this cleared out a huge amount of built-up liver fat.
- The trade-off: turning up the furnace also makes your heart beat a little faster — like gently revving an engine. This is the main thing to keep an eye on (see the warning signs later).
Why three buttons beat one
One button (appetite) works. Two buttons (appetite + comfort) work better. Three buttons (appetite + comfort + furnace) pull together — turning the tap down and opening the drain wider — which is why retatrutide out-loses everything before it.
How long it lasts
One dose keeps working in your body for about a week — it slowly drips away rather than switching off. That's exactly why you inject once a week: it keeps a nice steady level, like a time-release.
How it compares to Ozempic, Wegovy and Mounjaro
Remember the three "buttons"? That's the whole story of why retatrutide out-performs the others — they simply press fewer of them:
- Ozempic & Wegovy (semaglutide) press 1 button — appetite only.
- Mounjaro (tirzepatide) presses 2 buttons — appetite + the "smooth-the-ride" comfort button.
- Retatrutide presses all 3 — appetite + comfort + the "furnace" that actually burns fat and lifts your metabolism.
More buttons, more result. Here's how the big human trials stack up:
| Ozempic / Wegovy | Mounjaro | Retatrutide | |
|---|---|---|---|
| Hormone "buttons" | 1 | 2 | 3 |
| Average weight lost | ~15% | ~21% | ~24% |
| Burns fat & lifts metabolism | No | No | Yes |
| Liver fat cleared | Some | More | Most (~82%) |
| Record for weight loss? | No | No | Yes — most of any weight-loss drug ever tested |
In plain English: the others turn your appetite down. Retatrutide turns your appetite down and turns your fat-burning up — that second half is why the numbers are bigger, and why it also strips more fat out of your liver than anything else tested.
Two more perks of that third "furnace" button:
- It burns fat, not muscle, for fuel. The furnace targets fat specifically — so as long as you keep your protein up and do a little resistance work, the weight you lose comes off as fat while your muscle stays put.
- Your food works harder. It nudges your resting metabolism up and helps your body handle blood sugar better, so more of what you do eat gets used for energy instead of stored.
The honest bit (so you go in with your eyes open): retatrutide is the newest of the three. Ozempic and Mounjaro already have years of large safety studies and full approval behind them; retatrutide is still finishing its final trials. Its extra power also nudges your heart rate up a little more than the others do. So it's the strongest for weight loss — but because it's the newest, the smart move is exactly what this guide says: start low and pay attention to how you feel.
How fast it works — and when you'll see it
Two clocks are ticking, and it helps to know both.
In your body, one weekly shot peaks fast, then fades slowly:
And because you take it every week, each shot stacks on what's left of the last — so your level climbs for about a month, then holds steady:
What you'll notice runs on a longer clock — you feel it before you see it:
Quick version: it peaks 1–2 days after each shot and has a ~6-day half-life, so the doses overlap and build to full strength over your first ~5 weeks. Don't judge week one by the scale — judge it by your appetite first, and give the visible results time to catch up.
The one idea that makes dosing simple
Your vial is already mixed at one strength:
30 mg of retatrutide in every 1 mL of liquid.
(That's a 60 mg vial dissolved in 2 mL.) Once you know that, dosing is just measuring — think of it like squash concentrate: you know how strong it is, so you know how much to draw for any dose.
A few words you'll see (explained once, in plain terms):
| Word | What it means |
|---|---|
| Vial | The little glass bottle your retatrutide comes in. |
| mg | Milligram — a measure of how much drug. |
| mL | Millilitre — a measure of how much liquid. |
| Subcutaneous / "subQ" | Into the soft fat layer just under your skin (not into muscle). |
| Units | The small numbers printed on the side of an insulin syringe. That's what you'll measure your dose in. |
How the syringe numbers work (important, but easy)
You're using U-100 insulin syringes — the numbers on the side are called units, and there are 100 units in 1 mL.
Because your vial is 30 mg in every 1 mL, here's the magic conversion:
1 unit on the syringe = 0.3 mg of retatrutide.
So to work out how many units to draw for any dose:
Units to draw = your dose in mg ÷ 0.3
You don't have to do the maths — the chart further down does it for you.
What you'll need
- Your retatrutide vial (already mixed — 30 mg in every 1 mL)
- U-100 insulin syringes — 30 G, 8 mm, 0.3 mL (BD Micro-Fine; the kind with unit numbers on the side)
- Alcohol wipes (the little sachets)
- A sharps bin (a proper container for used needles)
- A fridge to keep the vial in
Step 1 — How much to draw (your dosing chart)
Find your dose in the left column, then draw that many units on the insulin syringe.
| Your weekly dose | Draw this many units | Roughly where to fill to |
|---|---|---|
| 1 mg — starting dose (weeks 1–2) | ~3 units (3.3) | just past the 3 line |
| 2 mg | ~7 units (6.7) | just past the 6½ line |
| 3 mg — enough for many people | 10 units | the 10 line |
| 4 mg | ~13 units (13.3) | just past the 13 line |
| 5 mg — common average for weight loss | ~17 units (16.7) | just past the 16½ line |
| 6 mg | 20 units | the 20 line |
| 7.5 mg — ⛔ absolute maximum, never go higher | 25 units | the 25 line |
Tip: the round-number doses — 3 mg = 10 units, 6 mg = 20 units, 7.5 mg = 25 units — are the easiest to measure exactly, because they land right on a printed line. For 1 mg, just fill to a little past the 3-unit line; rounding to 3 units is fine.
(How to choose your dose and when to go up is in Step 5 below — read that before you pick a number.)
Step 2 — Fill the syringe
- Wipe the rubber top of your vial with an alcohol wipe.
- Push the insulin syringe needle through the top.
- Turn the vial upside down, with the needle tip sitting in the liquid, and pull the plunger to draw a little past your target number of units.
- Get rid of air bubbles: hold the syringe with the needle pointing up, tap the side so bubbles float to the top, then gently push the plunger until they're out and the liquid is exactly on your target unit line.
- Pull the needle out. You're ready.
(A bit of air under the skin won't hurt you — but bubbles make your dose wrong, so tap them out.)
Step 3 — Inject it (under the skin)
You're using a 30 G, 8 mm needle — very thin and short, designed exactly for this. It goes into the soft fat just under the skin — not into muscle.
Where to inject (pick one, and use a different spot each week):
- Belly — anywhere except a 2-inch (5 cm) circle around your belly button
- Love handles / sides of your waist
- Front or outer thigh
- Back of the upper arm
How to do it:
- Wipe the spot with an alcohol wipe and let it dry.
- Pinch up a fold of skin and fat, then push the needle straight in at 90° (or at 45° if you're lean). The pinch keeps the dose in the fat, not the muscle.
- Push the needle all the way in, then press the plunger slowly until it's empty.
- Pull the needle straight out. Press a clean tissue on the spot for a moment — don't rub.
- Put the used syringe straight in your sharps bin. Never re-cap and reuse it.
Pick one day a week and stick to it (e.g. every Sunday). The drug stays in your body for about a week, so same-day-each-week keeps things steady.
Step 4 — Storing your vial
- Keep it in the fridge (a normal fridge, roughly 2–8 °C / 36–46 °F).
- Never put it in the freezer — freezing ruins it.
- Keep it out of bright light.
- Once you start using it, use it within about 4–6 weeks. Throw it away sooner if it ever looks cloudy, coloured, or has floating bits.
One heads-up: a vial holds a lot of doses (at low weekly doses, many weeks' worth). But the liquid only stays good for around 4–6 weeks in the fridge once it's in use, so if you dose small, some of the vial may pass its best-before window before you finish it. That's normal — just don't expect one vial to stay perfect for many months.
Step 5 — What dose to use, and going up slowly
Start low. This is the single most important rule — it's what keeps the nausea and stomach upset manageable while your body gets used to the drug.
The plan most people should follow
Weeks 1–2: just 1 mg a week (about 3 units — a little past the 3 line). After that, step up slowly, and only as much as you actually need.
In plain English:
- Most people don't need much. For a lot of users, around 3 mg a week is enough to lose weight fairly quickly. More is not automatically better.
- The common "sweet spot" is about 5 mg a week — that's a typical average once you've worked up to it.
- Never go above 7.5 mg a week. That is your hard ceiling. Higher doses pile on risk (especially the faster heart rate from the "furnace" button) without much extra benefit for most people. The trial's top dose of 12 mg also slows your stomach too much — more nausea and feeling uncomfortably, bloatedly full — in exchange for weight loss you didn't need.
- Stay at the lowest dose that's working. If you're losing weight and feeling OK, there's no reason to climb. Only step up if your weight loss clearly stalls and you're tolerating your current dose well.
- Give each step at least 2–4 weeks before you decide to go higher.
A gentle example ramp (only climb as high as you need)
1 mg (weeks 1–2) → 2 mg → 3 mg (many people stop here) → 4 mg → 5 mg (common average) → 7.5 mg maximum — never higher.
Step 6 — Eat well, and take two simple supplements
Because retatrutide makes you eat a lot less, you can end up short on the good things your body normally gets from food. Two easy "insurance policies" are worth taking the whole time you're on it:
- A daily multivitamin — fills in the everyday vitamins and minerals you'd normally get from the meals you're now shrinking or skipping.
- Omega-3 (fish oil) — the healthy fat that's good for your heart and brain. Especially worth it here: you're eating less of it from food, and it supports your heart at a time when this drug can nudge your heart rate up.
And the big one, more important than any supplement: keep your protein up and don't undereat. Even when you're not hungry, aim to get enough protein (meat, fish, eggs, dairy, protein shakes). Eating too little makes you lose muscle instead of just fat, and leaves you tired, weak, and foggy. The goal is to lose fat while staying strong — not to simply eat as little as possible.
Step 7 — Warning signs: when to stop and get help
Most side effects are mild (feeling a bit sick, less hungry, constipation). But stop and see a doctor if you get:
- Severe or lasting stomach pain, especially if it spreads to your back — this can be a sign of a serious pancreas problem.
- A racing or pounding heart you can't explain (remember, the "furnace" button can raise your heart rate — worth keeping an eye on).
- Pain in your upper-right belly, fever, or yellowing of the skin/eyes — possible gallbladder trouble.
- Spreading redness, warmth, or pus at an injection spot — a possible infection.
Step 8 — A quick honesty check on quality
- Retatrutide isn't approved or sold by pharmacies, so quality varies a lot between sources.
- Fakes and weak or impure product are common. If your supplier offers a purity test certificate (an "HPLC report") for your batch, that's a good sign. If they can't, be very cautious.
- What's written on the label might not match what's really in the vial.
Stick-on-the-fridge cheat sheet
YOUR VIAL: 30 mg in every 1 mL (60 mg in 2 mL, already mixed)
1 unit on the syringe = 0.3 mg
DOSE DRAW
1 mg (start, weeks 1-2) 3 units
2 mg 7 units
3 mg (enough for many) 10 units
5 mg (common average) 17 units
7.5 mg (NEVER go higher) 25 units
DOSING: Start 1 mg/week for 2 weeks, then go up slowly, only as needed.
Most people: 3 mg is plenty. Average: ~5 mg. Hard cap: 7.5 mg.
NEEDLE: 30 G, 8 mm — into a pinch of belly fat, once a week.
SPOTS: belly / love handles / thigh / back of arm — change each week.
STORE: fridge. NEVER freeze. Use within about 4-6 weeks.
EXTRAS: daily multivitamin + omega-3. Keep protein up. Don't undereat.
CAREFUL: bad stomach/back pain, racing heart → stop, see a doctor.
How trustworthy is each part of this guide?
(Plain-English version of the evidence behind it — so you know what's solid and what's a sensible best-guess.)
- The dose maths (30 mg/mL, the units) — rock solid. It's just arithmetic; the numbers can't be wrong.
- How the drug works (the three "buttons") — from real human trials and well-established biology. The three-hormone action and the record weight-loss numbers are genuinely proven.
- The muscle & metabolism perks — based on how the drug works, not a special study. They follow from its biology (it burns fat for fuel, raises resting metabolism) plus you keeping your protein up — sensible expectations, not a cast-iron guarantee.
- The dosing plan here (start 1 mg, most people ~3 mg, average ~5 mg, never above 7.5 mg) is a deliberately cautious, real-world approach — not a copy of the medical trial. The big trial actually pushed doses all the way to 12 mg. Going gentler than that trades a little extra weight loss for a lot less risk (especially on heart rate). Treat these numbers as sensible practical guidance rather than "the official study dose."
- How long the liquid lasts once in use (4–6 weeks) — an estimate, based on how similar injectable drugs behave, not formally measured for this exact one.
- Injection and storage technique — standard, widely-used practice, not something formally tested for retatrutide specifically.
Where the facts come from
Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine, 2023. (The three-hormone action and record weight-loss results; the trial's own dose range went up to 12 mg — this guide recommends a gentler cap.)
Coskun T, et al. LY3437943 … from discovery to clinical proof of concept. Cell Metabolism, 2022. (How the drug hits all three receptors, and how long it lasts in the body — about a week.)
Dose plan (1 mg start, ~3 mg for many, ~5 mg average, 7.5 mg ceiling), the supplement advice, and the injecting/storage steps: cautious real-world practice, chosen to be safer than the trial's top doses. Exact in-use shelf-life for retatrutide hasn't been formally published.
Comparison figures come from each drug's own large trials — semaglutide (STEP programme, ~15%), tirzepatide (SURMOUNT-1, ~21%), retatrutide (Jastreboff 2023, ~24%). No trial has yet pitted all three head-to-head, so these are separate-study figures, not a direct race.
Full science, mechanism, and cautions: see the main dossier → compounds/retatrutide.md.