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Formats 3 min read

Peptide pens and vials

Research peptides are supplied in three formats: lyophilised vials, pre-mixed vials and pre-mixed pens. They hold the same compounds. What differs is how much preparation is left to the laboratory.

HP Written by the Hello Peptides lab team · Updated October 2026

The three formats

FormatWhat arrivesPreparation
Lyophilised vialA freeze-dried powder under a rubber stopperMust be reconstituted with bacteriostatic water before use
Pre-mixed vialThe peptide already in solution, in a sealed vialNone. Drawn from the vial with a syringe
Pre-mixed penThe peptide in solution inside a dial-operated penNone. The dial sets the volume dispensed

What a peptide pen is

A peptide pen holds a pre-mixed solution in a cartridge and dispenses it through a dial mechanism. Turning the dial sets a volume, and the pen dispenses that volume each time. In laboratory use the appeal is repeatability: the same measured volume without drawing each one by hand.

A pre-mixed peptide pen removes two steps that introduce error with a lyophilised vial. There is no reconstitution, so there is no concentration to calculate, and no syringe to read.

Pens against vials

  • Pens are quicker to work with and dispense a consistent volume.
  • Pre-mixed vials give the same ready-to-use solution and suit work where volumes vary from one draw to the next.
  • Lyophilised vials keep longest unopened and let the laboratory choose its own concentration, at the cost of the preparation.
  • Anything pre-mixed, pen or vial, must be refrigerated at 2–8°C and never frozen.

Which of our products are pens

Our two stacks are the pen-format products. The glow stack combines GHK-Cu, BPC-157 and TB-500, and the klow stack adds KPV. Single compounds, including BPC-157, TB-500, GHK-Cu and bremelanotide, are supplied as 3ml pre-mixed vials.

We do not currently sell a single-compound BPC-157 pen or GHK-Cu pen. Both compounds are in the glow and klow pens, and each is available alone as a pre-mixed vial.

What to check on a pen

  • The total mass of each peptide and the volume of solution, which together give the concentration.
  • A batch number on the pen itself, matching the certificate.
  • For a blend, a certificate that identifies every component, not only the largest.
  • That it arrived cold. A pre-mixed product that has been warm in transit should be queried before it is used.

Storing a pen

Treat a pen exactly as you would a pre-mixed vial: refrigerate on arrival, keep it out of the light, and do not freeze it. Storing peptides has the detail.

Research use onlyPens are supplied as a laboratory dispensing format. They are not medical devices and are not supplied for human or animal use.

Common questions

Does a peptide pen need reconstitution? No. A pre-mixed pen arrives in solution. Reconstitution applies only to lyophilised vials.

Can a peptide pen be frozen? No. Freezing a solution can damage the peptide and the pen mechanism. Keep it at 2–8°C.

Is the compound in a pen different from the one in a vial? No. The format changes how the solution is dispensed, not what is in it.

Research use onlyProducts are supplied for laboratory research and are not for human or animal consumption, diagnosis or treatment. Questions about a batch? Contact the lab with the batch number.
Keep reading All guides →
Stacks Glow vs klow: what is the difference? The glow blend holds three peptides and the klow blend holds four. The difference is one compound: KPV. 2 min read Storage Storing peptides Lyophilised or pre-mixed, fridge or freezer, and how long each keeps. 5 min read Buying Buying research peptides in the UK What separates a careful UK peptide supplier from a careless one, and what to check before you order. 3 min read
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