Two items in our range arrive as a ready-made solution in a pen rather than as powder in a vial: tirzepatide and retatrutide from Nouveaux Ltd., both 40 mg. The pen works out cheaper per milligram and removes the reconstitution step, but in exchange it holds a solution that keeps less well than lyophilised powder. Below are both sides of the choice, with figures from the price list.
What you get in a pen and what in a vial
A vial contains lyophilised powder, freeze-dried, which has no concentration of its own. The concentration only appears once bacteriostatic water is added, and you decide how much to add. A pen contains a solution prepared by the manufacturer, at a concentration set in the factory.
Every other difference follows from this one. Powder keeps better and tolerates longer storage, while a ready solution needs the fridge from day one and has a shorter shelf life. Conditions for both forms are in the guide to powder and ready solution.
What a milligram costs in each
| Form | Contents | Price | Price per milligram |
|---|---|---|---|
| Pen, Nouveaux Ltd. | 40 mg of ready solution | 350 EUR | 8.75 EUR |
| Vial, Bio-Peptide or Genheal | 20 mg of powder | 200 EUR | 10 EUR |
The arithmetic favours the pen, and this applies to both molecules, because tirzepatide and retatrutide are priced identically in our shop. The difference is 1.25 EUR per milligram, or 50 EUR when buying forty milligrams.
What the pen does not give you
The pen takes away your choice of concentration. A 20 mg vial with 2 ml of bacteriostatic water gives 10 mg per millilitre, and with 4 ml half that, so you set how much solution corresponds to the same amount of substance. In the pen that decision has already been made, and the calculation comes down to reading the scale on the injector.
The second point is time. Powder can be kept and dissolved when you want to start, while the solution in a pen ages from the moment you buy it. At 40 mg, against the highest weekly doses in trials of 15 mg for tirzepatide and 12 mg for retatrutide, one pack lasts many weeks, and that time really matters.
What about calculating the dose
With a vial you do the arithmetic yourself, and it is the main source of mistakes. At a concentration of 10 mg per millilitre the volumes needed for a single dose are very small, and a slip of one decimal place changes everything. The conversion from milligrams to syringe units is covered in the guide to converting a peptide dose, and step-by-step dissolving in the guide to reconstitution.
We give no administration protocols here. The doses mentioned above come from clinical trials of approved medicines, and research material has no established dose, no leaflet and none of the control a pharmacy product has. This is explained in the guide to why semaglutide and tirzepatide are prescription only.
Which option suits whom
| Pen with ready solution | Vial with powder |
|---|---|
| Lower price per milligram, 8.75 EUR against 10 EUR | Higher price per milligram |
| No dissolving and no concentration calculations of your own | You set the concentration with the amount of water |
| Solution in the fridge from the start, shorter shelf life | Powder keeps better, the clock starts after dissolving |
| One 40 mg pack | Two brands to choose from, 20 mg each |
Both pens are in the weight loss peptides category. You check the packaging is original the same way as with a vial, following the instructions on the check your product page.
Frequently asked questions
Is a pen cheaper than a vial?
Per milligram, yes. A 40 mg pen at 350 EUR gives 8.75 EUR per milligram, and a 20 mg vial at 200 EUR gives 10 EUR.
Does a pen need to be kept in the fridge?
Yes, because it contains a ready solution. Powder in a vial keeps better and needs chilling only after dissolving.
Can the concentration in a pen be changed?
No. The manufacturer sets the concentration, and you read the scale on the injector. In a vial the concentration depends on the amount of water added.
Which products do we sell in pens?
Tirzepatide and retatrutide from Nouveaux Ltd., both 40 mg.
Does a pen mean it is a medicine?
No. The form of the pack does not change the status. We sell both products as material for laboratory research.
This is information about products and their form, not medical advice. Choosing a dose is up to a doctor.
Sources
- Jastreboff AM, Aronne LJ, Ahmad NN et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1 trial). New England Journal of Medicine, 2022, 387(3): 205-216. https://doi.org/10.1056/NEJMoa2206038
- Jastreboff AM, Kaplan LM, Frías JP et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. New England Journal of Medicine, 2023, 389(6): 514-526. https://doi.org/10.1056/NEJMoa2301972