How Long Do Reconstituted Peptides Last? What Stability Studies Actually Measured
Last updated: October 2, 2026 · 8 min read · By the Grey Peptides Editorial Board
- There is no single shelf life for a mixed peptide. Fourteen approved labels read for this guide allow anywhere from 3 hours to 60 days, depending on the drug and its formulation.
- The folklore figure, '30 days', matches no rule. The nearest real rule is CDC's 28 days for an opened multi-dose vial, which a product's own label overrides.
- Peptides are sold as powder because powder keeps. Protein and peptide drugs are made into solids to reach an acceptable shelf life, and once dissolved they start losing it.
- A pen's in-use period, such as semaglutide's 56 days after first use, belongs to that pen's formulation. It says nothing about a vial of the same molecule mixed at home.
The 30-day answer, and why it has no source
Ask how long a mixed peptide lasts and the most common answer is a month, sometimes 28 days, sometimes 30, usually with "in the fridge" attached. It sounds like a rule. It is not one, and the labels of approved peptide drugs, which are the only documents that state a period for a specific product, show why.
The closest real rule is about vials, not peptides. CDC's injection-safety guidance says an opened multi-dose vial should be dated and discarded within 28 days unless the manufacturer gives another date, and that the manufacturer's date wins in either direction. Our guide to bacteriostatic water explains where that comes from. It is a default for a preserved vial when a label is silent, not a measurement of how long any drug stays potent once it is dissolved.
Where manufacturers do state a period, the answers are nowhere near uniform. The labels below run from a few hours to two months.
Why peptides come as powder
Most injectable peptides that need mixing arrive as a freeze-dried powder, and that is a stability decision, not a convenience. A review of solid protein drugs puts it plainly: because of their limited physical and chemical stability, proteins often have to be made into solid forms to achieve an acceptable shelf life, and freeze-drying, or lyophilization, is the most common way to do it 1. The same review notes that freeze-drying is not gentle. Freezing and drying both stress the molecule, and even a successfully dried protein may have limited long-term stability 1.
Once the powder is dissolved, the clock speeds up. A widely cited review of protein drug stability describes two broad kinds of failure: chemical instability, where the molecule's bonds change, and physical instability, where its shape changes or molecules stick together, and it treats stabilisation in solution and in the dried state as separate problems with separate solutions 2. Peptides are smaller than most proteins, but the same logic applies to their formulations: the dry form is chosen because it keeps, and the solution is the fragile stage.
That is why the useful question is not how long a peptide lasts, but how long a particular solution, made a particular way, was shown to last. Only testing of that product can answer it.
What the labels measured: hours to two months
The table gathers the in-use periods printed on the labels of ten approved products that start as powder or ready-made vials. Each period is the label's own wording, condensed; the evidence grade links to the drug's encyclopedia entry.
| Drug (product) | What you start with | How long the label allows | Evidence grade |
|---|---|---|---|
| Teduglutide (Gattex) | Powder mixed with sterile water | Give within 3 hours of mixing 3 | High |
| Vosoritide (Voxzogo) | Powder mixed with the diluent supplied | Up to 3 hours in the vial at room temperature 4 | High |
| Rusfertide (Mimrylo) | Powder for reconstitution | As soon as possible, and no later than 4 hours 5 | High |
| Lonapegsomatropin (Skytrofa) | Cartridge reconstituted in its device | Within 4 hours at room temperature 6 | High |
| Tesamorelin (Egrifta SV) | Powder mixed with sterile water | Immediately; do not refrigerate or freeze the mixed solution 7 | High |
| Tesamorelin (Egrifta WR) | Powder mixed with bacteriostatic water | Discard 7 days after mixing 8 | High |
| Elamipretide (Forzinity) | Ready-made solution in vials | Discard vials 8 days after first opening 9 | High |
| Follitropin alfa (Gonal-f multi-dose) | Powder mixed with bacteriostatic water | Discard unused solution after 28 days 10 | High |
| Somatropin (Humatrope) | Reconstituted cartridge | Up to 28 days refrigerated 11 | High |
| Chorionic gonadotropin (Pregnyl) | Powder for reconstitution | Stable for 60 days refrigerated 12 | High |
Three things stand out. First, the spread: teduglutide and vosoritide allow about 3 hours, follitropin alfa and somatropin 28 days, and one chorionic gonadotropin product 60 days in the fridge 3 4 10 11 12. Second, the short periods are not obscure exceptions; they belong to newer drugs whose labels say the mixed solution should be used the same day. Third, tesamorelin appears twice. Mixed with sterile water in its single-dose form, it is to be used at once and the solution is not to be refrigerated; mixed with bacteriostatic water in its multi-dose form, it lasts 7 days 7 8. Same molecule, same company, two answers, because the formulation and the diluent differ.
Each is the period printed on that product's label, approved with it. None of them is a general rule for the molecule, let alone for peptides as a class.
Pens are a different question
The other common reference point is the injection pen, and pens can last a long time after first use. The labels read for this guide give these periods:
| Drug (product) | What you start with | How long the label allows | Evidence grade |
|---|---|---|---|
| Teriparatide (Forteo) | Ready-to-use pen | Discard 28 days after first use 13 | High |
| Liraglutide (Victoza) | Ready-to-use pen | 30 days after first use, at room temperature or refrigerated 14 | High |
| Semaglutide (Wegovy FlexTouch) | Ready-to-use multi-dose pen | 56 days after first use, at 15-30 °C or refrigerated 15 | High |
| Tirzepatide (Mounjaro single-dose pen) | Ready-to-use single-dose pen | Up to 21 days in total out of the fridge, at no more than 30 °C 16 | High |
These are the periods the labels state 13 14 15 16. They are also tied to the pen. A ready-to-use pen contains a finished liquid formulation, with buffers, preservatives and stabilisers chosen for it and tested in it, in a closed cartridge that is entered only by a fresh needle. Semaglutide's 56 days belongs to the Wegovy FlexTouch pen, not to semaglutide. A powder of the same molecule, mixed in a vial with whatever diluent is at hand, has no tested period at all.
The tirzepatide row shows another distinction the labels draw: time out of the fridge is counted separately from time after first use. Its single-dose pens may spend up to 21 days in total at no more than 30 °C before use 16. Wegovy's single-dose pens and syringes may be kept at 8 to 30 °C for up to 28 days before the cap is removed 15. Those allowances are for unopened products, not for anything mixed.
Heat, cold and freezing
Refrigeration is the usual instruction, but it is not universal. Egrifta SV's label says the mixed solution should not be refrigerated or frozen; it is meant to be used at once 7. Several of the short periods in the first table are explicitly room-temperature periods 4 5 6. The label, not habit, decides where a mixed solution goes.
Room-temperature allowances on unopened pens show that manufacturers test excursions and set limits on them, typically with a ceiling of 30 °C and a maximum number of days 16 15. A vial left in a hot car or posted in summer has had an excursion nobody measured.
Freezing deserves particular caution. The freeze-drying review describes freezing as one of the stresses that can denature proteins during manufacture, under controlled conditions and with stabilisers present 1. A dissolved peptide frozen in a household freezer has none of those controls, and labels that address it tell users not to freeze.
What you can and cannot see
Labels ask users to look before injecting. The tesamorelin labels, for example, say to use the mixed solution only if it is clear, colourless and free of particles 7 8. Cloudiness, colour or flecks are reasons to discard.
The reverse does not hold. A solution can look perfect and have lost potency, because the chemical changes that matter, the ones the stability reviews describe, are invisible 2. Appearance can rule a vial out; it cannot rule one in.
What this means for unapproved peptides
Every period in this guide comes from a label approved with a specific product and formulation. Peptides sold for "research use" have no label, so they have no tested in-use period, no tested storage temperature and no tested diluent. The common advice to keep a mixed vial for about a month borrows a number from somewhere else.
The labels do allow a few general conclusions. A mixed solution is less stable than the powder it came from 1. Label periods for approved peptides vary more than a hundredfold, so no single figure can be applied to an untested one. The formulation and the diluent change the answer even for the same molecule 7 8. And an opened multi-dose vial is dated from first use, with clinics discarding it within 28 days where no label says otherwise, as our bacteriostatic water guide explains.
For mixing arithmetic, the site's reconstitution calculator and reconstitution guide cover volumes and concentrations. For what independent laboratories have found in products sold online, see independent lab results. None of this is medical advice; for anything you would inject, a pharmacist or clinician who can see the product's own documentation is the person to ask.
Frequently asked questions
How long do peptides last after reconstitution?
It depends on the product. Approved labels allow anywhere from about 3 hours (teduglutide, vosoritide) to 28 days (follitropin alfa, somatropin) and, for one chorionic gonadotropin product, 60 days refrigerated.
Is 30 days a safe rule for mixed peptides?
No label supports it. The nearest real rule is CDC's 28 days for an opened multi-dose vial, which a product's own label overrides, and label periods for approved peptides vary more than a hundredfold.
Do peptides need to be refrigerated after mixing?
Usually, but not always: one tesamorelin product's label says not to refrigerate or freeze the mixed solution and to use it at once. The product's label decides.
Do peptides expire before mixing?
Yes. Unopened products carry an expiry date, and freeze-dried powders are used because they keep far longer than solutions, though even dried proteins have limited long-term stability.
Why does a semaglutide pen last 56 days?
Because that pen's formulation was tested for it. The 56 days belongs to the Wegovy FlexTouch pen, not to semaglutide powder mixed in a vial.
Can you tell if a mixed peptide has gone off?
Only partly. Cloudiness, colour or particles mean discard, but a clear solution can still have lost potency, because the important chemical changes are invisible.
Related on Grey Peptides
- Bacteriostatic water vs sterile water vs saline
- How to Reconstitute Peptides
- Reconstitution calculator
- Independent lab results
Sources
- Wang, W. (2000). Lyophilization and development of solid protein pharmaceuticals. Int J Pharm. PMID: 10967427
- Manning, M. C. et al. (2010). Stability of protein pharmaceuticals: an update. Pharm Res. PMID: 20143256
- Takeda Pharmaceuticals America. Gattex (teduglutide) for injection. Prescribing information, DailyMed set 66b69c1e-b25c-44d3-b5ff-1c1de9a516fa, version 20, effective 2025-09-05; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- BioMarin Pharmaceutical. Voxzogo (vosoritide) for injection. Prescribing information, DailyMed set 228e8560-04a4-4bb1-a81f-29531a9e4d27, version 16, effective 2025-11-25; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- Takeda Pharmaceuticals America. Mimrylo (rusfertide). Prescribing information, DailyMed set 101aff01-31ed-4841-a8b6-0a5a8503189b, version 2, effective 2026-08-28; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- Ascendis Pharma. Skytrofa (lonapegsomatropin-tcgd) for injection. Prescribing information, DailyMed set 9229f871-bc61-4ddc-8122-d126d40e36ac, version 13, effective 2026-07-23; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- Theratechnologies Inc.. Egrifta SV (tesamorelin for injection). Prescribing information, DailyMed set 3d783378-b02d-4f19-99dd-0fc91a042224, version 9, effective 2026-07-29; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- Theratechnologies Inc.. Egrifta WR (tesamorelin for injection). Prescribing information, DailyMed set 839334d3-8c1d-4c26-9036-2ab524a6ea75, version 2, effective 2026-07-29; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- Stealth BioTherapeutics. Forzinity (elamipretide) injection. Prescribing information, DailyMed set 146bf34c-76f2-48db-ac07-fb29cce2cd75, version 10, effective 2025-12-10; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- EMD Serono. Gonal-f (follitropin alfa for injection). Prescribing information, DailyMed set ae85b9c3-e7eb-4981-a5d9-346050e8f189, version 15, effective 2025-09-02; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- Eli Lilly and Company. Humatrope (somatropin) for injection. Prescribing information, DailyMed set a774e1ae-3997-49ee-8b0e-99a2b315d409, version 45, effective 2026-08-20; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- Organon LLC. Pregnyl (chorionic gonadotropin for injection). Prescribing information, DailyMed set 1e94155f-19be-4944-b197-be4edbb4faf9, version 11, effective 2025-12-02; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- Eli Lilly and Company. Forteo (teriparatide) injection. Prescribing information, DailyMed set aae667c5-381f-4f92-93df-2ed6158d07b0, version 44, effective 2026-08-03; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- Novo Nordisk. Victoza (liraglutide) injection. Prescribing information, DailyMed set 5a9ef4ea-c76a-4d34-a604-27c5b505f5a4, version 31, effective 2025-10-14; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- Novo Nordisk. Wegovy (semaglutide) injection. Prescribing information, DailyMed set ee06186f-2aa3-4990-a760-757579d8f77b, version 19, effective 2026-06-18; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
- Eli Lilly and Company. Mounjaro (tirzepatide) injection. Prescribing information, DailyMed set d2d7da5d-ad07-4228-955f-cf7e355c8cc0, version 40, effective 2026-08-27; read October 2, 2026. Cited without a link; the set id finds it on DailyMed.
Educational information, not medical advice. Each dose in this guide names its source, an approved label or a published study. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. This guide reports what product labels and published reviews say; it does not name or link to any seller, and it is not medical advice.
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