Store retatrutide refrigerated (2–8 °C), dry and in the dark. This storage advice is printed on the label of both the pre-filled pen and the vial of lyophilised powder. Do not freeze a pen. Keep a vial closed until you need it; once dissolved, the material is less stable, so keeping it cold, dark and for as short a time as possible becomes even more important. The expiry date on the label applies to the unopened product, stored as directed.
Below, we explain what to do in each situation, and why. No studies on the stability of retatrutide as research material have been published, so the advice follows the label and what the literature says about peptides in general.
Storage by form and situation
| Situation | Temperature | What to watch out for |
|---|---|---|
| Pen, unused | 2–8 °C (fridge) | Do not freeze; keep in the box to protect from light |
| Vial, unopened | 2–8 °C (as per label) | Closed, dry and dark; if taken from the freezer, let it reach room temperature first |
| Vial, dissolved | Fridge; for longer periods, frozen in portions only | Keep for as short a time as possible; avoid repeated freezing and thawing |
| In transit | Ambient temperature | Put in the fridge as soon as it arrives |
Temperature: fridge, freezer or room temperature
Heat speeds up the chemical reactions by which peptides degrade, such as deamidation, oxidation and hydrolysis [1]. This is also why many peptide medicines are stored and transported in a cold chain [1]. For Clean Peptides retatrutide, the label specifies 2–8 °C: an ordinary fridge. Keep the product on a shelf rather than in the door, where the temperature fluctuates most as the fridge is opened and closed.
For dry peptide powder, manufacturers recommend −20 °C or colder for longer-term storage [2][3]. If you use the freezer, let the closed vial warm to room temperature before opening it, preferably in a desiccator; otherwise condensation will form on the cold powder [2][3].
A pen contains a solution, and a solution should not be frozen. Freezing and thawing can cause peptides in solution to clump together (aggregate) [1]. Shaking and heat can do the same, so do not leave a pen in a hot car or on a radiator.
Light
Light can trigger oxidation. The amino acid tryptophan is particularly sensitive to it; tyrosine, phenylalanine and cystine can also be altered by light [1]. How seriously light sensitivity is taken is clear from the fact that there is a separate international guideline for photostability testing of new active substances (ICH Q1B) [4]. In practice, this means keeping the pen and vial in their box, not leaving them on a windowsill and keeping their time under bright lamps to a minimum.
Moisture and condensation
For a vial of powder, moisture is the greatest risk. Peptide powder readily absorbs water from the air, which lowers the peptide content per milligram of powder and can reduce stability [3]. Sigma-Aldrich notes that exposure to moisture greatly shortens long-term shelf life [2]. So do not open a vial more often than necessary, and reseal it straight away.
Shelf life: what the expiry date does and does not tell you
The expiry date on the label assumes an unopened pack, stored as directed. Once the powder has been dissolved, that date tells you nothing about the solution. As a general guideline for peptides in solution, Sigma-Aldrich gives about one week at 4 °C. For longer storage, it recommends freezing portions (aliquots) at −20 °C for one to two weeks, or at −80 °C for longer, and avoiding repeated freezing and thawing [2]. Bachem advises against storing peptide solutions for long periods at all [3]. These are guidelines for peptides in general, not measured values for retatrutide.
So record on the vial or in your lab notebook when you dissolved it, which solvent you used and in what volume. If a solution turns cloudy, contains flakes or changes colour, that is a sign that the peptide has changed.
Transport and receipt
We ship from the Netherlands. Within the Netherlands, parcels usually arrive one day after dispatch, and in Belgium and Germany after two days (median, measured from February to September 2026). Put the pen or vial in the fridge as soon as it arrives. If your parcel has been in transit much longer than that, or has been exposed to heat, please contact us and quote your order number.
How the pen and the vial differ in other respects is explained in Retatrutide pen or vial: what are the differences? For general storage tips for other peptides, see How to store peptides. All pens and vials are listed on the retatrutide page; questions about shipping and payment are answered in the frequently asked questions.
Further reading
- Retatrutide: overview and strengths
- Retatrutide pen or vial: what are the differences?
- How do you store peptides so they stay stable?
- Retatrutide vs semaglutide and tirzepatide: the differences
Sources
- Nugrahadi PP, Hinrichs WLJ, Frijlink HW, et al. Designing Formulation Strategies for Enhanced Stability of Therapeutic Peptides in Aqueous Solutions: A Review. Pharmaceutics 2023;15(3):935. doi:10.3390/pharmaceutics15030935
- Sigma-Aldrich (Merck). Handling and Storage Guidelines for Peptides and Proteins. sigmaaldrich.com (accessed 30 September 2026)
- Bachem. Handling and Storage Guidelines for Peptides. bachem.com (accessed 30 September 2026)
- European Medicines Agency. ICH Q1B Photostability testing of new active substances and medicinal products (CPMP/ICH/279/95). ema.europa.eu
For laboratory research only. Clean Peptides products are not intended for use in humans or animals. This article provides general information and is not medical advice.
