How to Fill & Use Your Peptide Pen
Everything you need to set up, fill, and get the most out of your reusable peptide pen — step by step, in plain English.
I ordered my pen — now what?
Every RefillPen arrives ready to use: the pen, one 3 mL cartridge, and the tools to get started the day it lands on your doorstep. When a cartridge runs out, you fill a fresh one and load it — you keep the pen.
New to filling cartridges? Follow the 3 mL cartridge filling guide, then come back here to load and dial your pen.
Set up & load a cartridge
- 1Pull the pen cap off.
- 2Unscrew the cartridge holder (the body of the pen) from the main pen body.
- 3Make sure the piston rod is fully pushed in.
- 4Insert the cartridge into the holder, metal-capped (threaded) end first.
- 5Screw the cartridge holder back onto the main pen body until it is secure.
Prime & swap cartridges
You can swap cartridges in and out of one pen — just re-prime each time. Line up the black plunger with the gray stopper and purge one unit to confirm it's correctly lined up before you dial a dose.
Dial your dose
Each number on the dial equals one unit. If you'd normally pull a syringe to 20, you simply dial the pen to 20 — one click, one unit.
Not sure how many units to dial? Use the peptide dosing calculator to find your units.
Choosing a needle tip
RefillPen uses universal pen needles in sizes 4, 5, 6, 8, 10, and 12 mm, available on Amazon or diabeticwarehouse.com. Pen needles are single-use — reusing one dulls the tip and can cause pain or a blockage.
Pen needles are made for subcutaneous injections (the longest, 12 mm, is ½ inch). On the V2, the 4–6 mm tips sit just below the cap and the 8–12 mm tips sit above it. Hold the injection for a count of 10–15 afterward so all the fluid empties — a little longer for larger amounts through a smaller tip.
Filling supplies: disposable luer lock (releases pressure while filling) and a plastic syringe for filling the glass cartridge.
Which pen — V1, V2, V2.5, or V3?
Want to see and feel the poke? Choose the V1 (up to 80 units) or the V3 (up to 60 units). Rather not see it, and feel less? Choose the V2 (shorter and chubbier) or the V2.5 (longer and slimmer). Both go up to 60 units. With a 4, 5 or 6 mm tip, the needle stays hidden, and the cap helps scramble the nerve signals on your skin.
V1
Slim metal body, up to 80 units, closed cap — you'll see and feel the injection (remove the cap to inject).
V2
Metal, up to 60 units, open cap — inject with the cap on or off. With the cap on and a 4–6 mm tip, the cap eases the feel and hides the needle.
V2.5
Slim Hybrid: the open-cap hidden-needle comfort in a lighter, slimmer body, with a 60-unit range.
V3
Slim metal body, up to 60 units, closed cap — you'll see the needle as you inject.
Still deciding? Compare them in the Best Reusable Peptide Pen guide or browse all pens.
Cartridges & accessories
RefillPen's 3 mL glass cartridges are double-sterilized and individually steamed. Each holds up to 3 mL and is single-use — dispose of it once the 3 mL is used. The pen itself is reusable; you just replace the cartridge.
Shipping
Orders process within 48 hours (usually within 24) and ship via USPS. Shipping is a flat rate by region, with free shipping on orders over $59 to the 48 contiguous states, and tracking is emailed to you. International: if you don't see your country at checkout, email your address and what you'd like, and we'll add it for you.
Still need help?
Email us at info@refillpen.com and we'll get you sorted, or browse the full FAQ.
Ready to get started?
Reusable peptide pens from $24.99, $1 sterilized cartridges, and free shipping on orders over $59.
Or try the free peptide dosing calculator →