A peptide pen is a reusable, pen-shaped tool for measuring out precise, repeatable amounts of liquid from a sealed glass cartridge. You set an amount on a dial, press a button, and a plunger rod moves the cartridge’s rubber stopper forward by exactly that much. The design comes from the pen-injector, which replaced the vial-and-syringe routine because a mechanical dial measures more consistently than reading a printed scale by eye. We explain why in Pen vs. Syringe.
The easiest way to understand one is to go through it part by part. We’ll use the PepPen V2, our most popular pen.
The parts, front to back
Pen needle. A small, single-use needle that screws onto the front of the pen. It’s sold separately in boxes of 100. Use a new one each time. Our needle guide explains the sizes.
Open spring end. On the V2, the front of the pen has an open spring end that covers the needle. It’s one of the main differences between the V2 and the closed-end models.
Front metal cover. This slides over the cartridge holder and protects the cartridge. It pulls straight off. Most new owners miss this the first time, then wonder where the holder went. Here’s where to find it.
Cartridge holder. This sits under the front cover, attached to the threads that join the pen’s two halves. On the V2 the cartridge drops into an open end, which makes loading quick.
3 mL glass cartridge. This holds the liquid. It’s a small glass tube with a rubber seal at the front, which the needle pierces, and a rubber stopper at the back. Every reusable PepPen takes the same standard cartridge. Learn more in What’s Actually in a 3 mL Glass Pen Cartridge.
Plunger rod. This sits inside the pen body. When you press the button, it pushes against the cartridge’s rubber stopper and moves it forward by the amount you dialed.
Dial. You turn it to set the amount. On the V2, each click is 0.01 mL, and you can set up to 0.60 mL per press. A full 3 mL cartridge is 300 clicks.
Button. Press it slowly, hold it down for about five seconds after the dial returns to zero, then lift. Holding it gives the liquid time to finish moving through the needle.
How it works in one cycle
- Fill a cartridge using a vent needle, so pressure doesn’t push the stopper out of position. Step-by-step guide.
- Load it into the holder under the front cover and screw the pen together.
- Attach a pen needle and purge the air. Dial a small amount, point the pen up, and press until liquid appears at the tip.
- Dial the amount you need, in 0.01 mL steps.
- Press and hold.
- Remove the needle and dispose of it safely.
The pen itself is reusable. The cartridge and the needles are the parts you replace.
Why start with the V2
The V2 is solid metal, quick to load, and has the simplest layout in our range, which is why most people start with it. Every PepPen ships fully assembled in its own bubble wrap, so it’s ready to load as soon as you have cartridges and needles. If you need everything at once, the Starter Kit includes cartridges, pen needles and vent needles.
If you want a cartridge that locks in, look at the V2 Pro. If you want the sturdiest build, look at the V1. Our comparison lays out all five.
Shop the PepPen V2 or watch the three short setup videos on our FAQ page.
All PepPens products are sold for research use only. They are not medical devices.
