How do you use a peptide pen?

Fit a fresh 32G pen needle, prime a new pen with 2 clicks until a drop forms, dial your dose in clicks using the card that ships with the pen, inject at 90° and hold for 10 seconds before withdrawing. Refrigerate at 2–8°C between doses.

Do you need to prime a peptide pen every time?

No — only when the pen is new or you've fitted a new needle. Priming clears air; between doses on the same needle you can dial straight to your dose.

How many clicks per mg on a peptide pen?

It depends on the vial strength and the reconstitution concentration inside the pen. Every Peptides UK 4U pen ships with a calibrated clicks-per-mg card matched to that specific fill.

How long does a peptide pen last?

Once reconstituted and refrigerated at 2–8°C, generally 4–6 weeks — or until the dial reaches the end of the cartridge, whichever comes first.

What needles fit a peptide pen?

Standard screw-on pen needles. We recommend 32G 6mm for minimum discomfort and stock them on-site.

How to Use a Peptide Pen — UK 2026 Cornerstone Guide

How to use a peptide pen in the UK: what a pre-filled Quick Pen is, priming, clicks-per-mg, dose selection, needle attachment, storage and troubleshooting — for Reta, Tirz and Sema pens.

For laboratory research and in vitro use only. Not for human or veterinary use.

A peptide pen is a standard dial-a-dose injection pen pre-loaded with a reconstituted research peptide. At Peptides UK 4U we prepare Retatrutide, Tirzepatide and Semaglutide as pre-filled Quick Pens in a controlled UK facility — the pen arrives calibrated with a clicks-per-mg card and ready to use. This guide covers every peptide pen in our range and applies whether you're using Reta 30mg, Tirz 40mg or Sema 30mg.

What is a pre-filled peptide pen?

A vial of lyophilised peptide has been reconstituted with bacteriostatic water inside a standard pen cartridge, at a fixed concentration. Because the concentration is set, the pen's dial can be used to deliver a repeatable dose in "clicks" — each click corresponds to a known mg amount for that specific fill.

1. Unbox and inspect

The pen ships in insulated cold packaging. Check the pen window: the solution should be clear and colourless. Cloudiness, particulates or discolouration are stability red flags — don't use the pen; contact us. Keep the included clicks-per-mg card with the pen.

2. Attach a fresh pen needle

Use a new 32G 6mm screw-on pen needle every dose. Peel the tab, screw on straight until snug, and remove the outer and inner caps.

3. Prime the pen (new pens only)

Dial to 2 clicks, point the needle upwards, tap the cartridge to move air to the top, and press the plunger until a bead of liquid forms on the needle tip. This clears air and confirms flow. Only prime a new pen or after fitting a new needle.

4. Dial your dose

Convert your mg target into clicks using the card that ships with the pen — every peptide pen ships calibrated. If you want a second opinion, use our free peptide reconstitution calculator to confirm.

5. Deliver the dose

Insert the needle at 90° into a clean site, press the plunger fully, and hold for 10 seconds before withdrawing. This ensures the full dose is delivered and reduces leakage.

6. Remove and dispose of the needle

Recap the outer needle cover, unscrew the used needle and drop it into a sharps bin. Never re-cap the inner cap by hand and never re-use a needle.

7. Storage between doses

Refrigerate at 2–8°C.
Keep out of direct light.
Never shake.
Reconstituted peptide pens are generally stable for around 4–6 weeks.

Common problems

Dial won't reach your dose — the pen is close to empty. Finish the remainder on a fresh pen and note the split.
No liquid on priming — needle is blocked. Fit a new one.
Cloudy solution — stop using it and contact us.
Bruising at the site — rotate sites and use a fresh 32G needle each time.

Peptide pens available in the UK

Retatrutide Pen UK — 20mg / 30mg / 40mg
Tirzepatide Pen UK — 20mg / 40mg / 60mg
Semaglutide Pen UK — 30mg

Or browse the full peptide pens UK range. Every pen is prepared in the UK, cold-shipped, and dispatched next-day via Royal Mail Tracked 24.

For In Vitro Use Only — Not for Human Use. Content is for laboratory research and educational purposes only.