GLP-3 RT (retatrutide) explained: how the triple agonist pen works

Three receptors, one weekly injection

Most well-known compounds in this class act on one receptor (GLP-1) or two (GLP-1 and GIP). Retatrutide adds glucagon receptor activity on top of both.

Each arm does something different, and the combination is what makes the profile distinctive:

• —GLP-1: slows gastric emptying and reduces appetite signalling, so meals feel satisfying much sooner.
• —GIP: supports insulin response to food and appears to improve how well the GLP-1 arm is tolerated.
• —Glucagon: raises energy expenditure — the body burns more at rest rather than only eating less.

What the published data shows

In the phase 2 obesity trial published in the New England Journal of Medicine (Jastreboff et al., 2023), participants on the highest retatrutide dose lost roughly 24% of body weight at 48 weeks, with the curve still trending downward at the end of the study.

That is the highest figure reported to date for a single incretin compound in a randomised trial, and it is the reason retatrutide gets so much attention compared with earlier molecules.

Why once a week is enough

Retatrutide has a long half-life, so one injection per week keeps blood levels inside a stable band instead of spiking and crashing. Stable levels mean fewer appetite rebounds between doses and far less injection burden than a daily protocol.

Pick one day of the week and stay on it. Consistency matters more than which day you choose.

Dosing the pen: 15 dials = 1 dose

Our pens are pre-filled and pre-reconstituted. You do not mix anything. Turn the dose dial to 15, inject, and that is your weekly dose for the pen strength you bought.

• —Set the dial to 15 — the pen only shows the number, not the unit.
• —Wipe the pen tip and the injection site with an alcohol pad.
• —Inject subcutaneously a few inches away from the belly button.
• —One pen covers four weekly doses — a full month.
• —Store in the fridge. Potency drops after 28 days in use.

Choosing a strength

We stock 2.5 mg, 3.5 mg and 5 mg per dose. Start at the lowest strength that fits your plan and only step up once side effects at the current level have settled.

Going up too quickly is the single most common reason people abandon this class of compound — nausea is dose-driven and almost always improves with patience rather than pushing through.

A realistic timeline

Weeks 1–2: appetite noticeably quieter, portions shrink on their own, some early water-weight movement.

Weeks 3–6: steady fat loss establishes, cravings and food noise fade, energy stabilises as the glucagon arm contributes.

Weeks 7–12: the trend becomes visible in clothes and photos; most people step up one strength around here.

Month 4+: the published curve keeps going. This is where the triple-agonist profile separates from single-receptor compounds.

Handling, cold chain and storage

The pen may arrive at room temperature. It is sealed and stable in transit, so this does not affect potency. Put it in the fridge when it arrives and keep it there between doses.

Every lot we list is independently tested for purity and identity, and the certificate for that exact lot is published at the bottom of the product page.