Do Peptides Expire?

That vial of BPC-157 in the back of your fridge — the one you reconstituted six weeks ago and forgot about. Is it still good? What about the sealed lyophilized peptide that's been sitting at room temperature since it arrived three months ago?

Peptides do expire. They degrade. And the rate at which they break down depends on their form (powder vs. solution), storage conditions (temperature, light, moisture), the specific peptide sequence, and whether preservatives are present.

Understanding peptide stability isn't academic — it directly affects whether you're getting an active product or injecting expensive degradation fragments.

Do Peptides Have Expiration Dates?
How Peptides Degrade
Lyophilized (Powder) vs. Reconstituted (Solution) Stability
Shelf Life by Peptide Form
Temperature and Storage Conditions
How to Tell If a Peptide Has Degraded
Specific Peptide Stability Data
Reconstitution and Post-Reconstitution Stability
Skincare Peptide Shelf Life
Frequently Asked Questions
The Bottom Line
References

Do Peptides Have Expiration Dates?

Yes. Every peptide product has a finite useful life, though the timeline varies enormously:

Lyophilized (freeze-dried) peptides stored properly: 2-5+ years
Reconstituted peptides in bacteriostatic water, refrigerated: 3-4 weeks
Reconstituted peptides in sterile water, refrigerated: 1-2 weeks
FDA-approved peptide drugs: Follow manufacturer's stated expiration (typically 2-3 years from manufacture for unopened product)
Topical peptide skincare products: 6-12 months after opening, 1-3 years unopened

These aren't arbitrary numbers. They reflect the chemistry of peptide degradation — the reactions that break peptide bonds, oxidize amino acid residues, and convert an active molecule into an inactive one [1].

How Peptides Degrade

Peptide degradation happens through several chemical pathways [2]:

Hydrolysis

Water molecules attack peptide bonds, breaking the chain into smaller fragments. This is the primary degradation pathway for peptides in solution. The rate depends on temperature, pH, and the specific amino acid sequence — some sequences are more vulnerable to hydrolysis than others.

Oxidation

Certain amino acids — methionine, cysteine, tryptophan, histidine, and tyrosine — are susceptible to oxidation by dissolved oxygen, metal ions, or light. Oxidation can alter the peptide's structure and biological activity. Methionine oxidation to methionine sulfoxide is one of the most common degradation products [3].

Deamidation

Asparagine and glutamine residues can lose their amide group, converting to aspartate and glutamate. This changes the peptide's charge and can affect receptor binding. Deamidation is accelerated by alkaline pH and higher temperatures.

Aggregation

Peptide molecules can stick together, forming dimers, oligomers, or larger aggregates. Aggregation reduces the concentration of active monomer and can create immunogenic species (aggregated proteins are more likely to trigger immune responses than monomers).

Racemization

L-amino acids can convert to their D-form (mirror image), especially at aspartate residues. Since biological receptors are stereospecific — they only recognize the L-form — racemization reduces biological activity.

Disulfide Bond Scrambling

Peptides containing cysteine residues (like oxytocin or some growth factors) have disulfide bonds that maintain their 3D structure. In solution, these bonds can break and reform in incorrect positions, producing misfolded, inactive peptide.

Lyophilized (Powder) vs. Reconstituted (Solution) Stability

This is the single most important distinction for peptide shelf life:

Lyophilized peptides are freeze-dried powders with minimal water content. With water removed, hydrolysis — the primary degradation pathway — is dramatically slowed. Deamidation, oxidation, and aggregation also slow down significantly in the dry state. Properly stored lyophilized peptides can retain >95% potency for years [4].

Reconstituted peptides are back in solution, and the degradation clock starts ticking. Every pathway listed above becomes active. The rate depends on:

Temperature (refrigerated is much better than room temperature)
pH (most peptides are most stable at mildly acidic pH, around 4-5)
Preservative (bacteriostatic water contains 0.9% benzyl alcohol, which inhibits microbial growth and extends usable life)
Light exposure (UV and visible light can drive photo-oxidation)
Container (glass vials are inert; some plastics can leach compounds or adsorb peptide)

This is why peptides are shipped as lyophilized powder rather than pre-mixed solutions — and why proper reconstitution and storage matter so much.

Shelf Life by Peptide Form

Form	Storage Condition	Expected Shelf Life
Lyophilized, sealed	-20°C (freezer)	3-5+ years
Lyophilized, sealed	2-8°C (refrigerator)	2-4 years
Lyophilized, sealed	Room temperature	6-12 months (variable)
Reconstituted in bacteriostatic water	2-8°C (refrigerator)	3-4 weeks
Reconstituted in sterile water	2-8°C (refrigerator)	7-14 days
Reconstituted, any diluent	Room temperature	24-48 hours
Topical cream/serum (opened)	Room temperature (cool, dark)	6-12 months
Topical cream/serum (unopened)	Room temperature	1-3 years

These are general guidelines. Specific peptides may be more or less stable depending on their amino acid sequence and any modifications.

Temperature and Storage Conditions

Temperature

Temperature is the single most important storage variable. As a general rule, every 10°C increase in temperature roughly doubles the rate of chemical degradation (the Arrhenius principle) [5].

-20°C to -80°C (freezer): Optimal for long-term storage of lyophilized peptides. Minimal degradation. Most research labs store peptide stocks at -20°C.
2-8°C (refrigerator): Good for both lyophilized and reconstituted peptides. The standard recommendation for reconstituted peptides in active use.
Room temperature (20-25°C): Acceptable for lyophilized peptides for short periods (weeks to months) but not ideal for long-term storage. Not acceptable for reconstituted peptides beyond 24-48 hours.
>30°C: Accelerated degradation. Peptides left in a hot car, warm mailbox, or uncontrolled shipping environment will lose potency faster.

Light

UV light and visible light can drive photo-oxidation reactions, particularly in peptides containing tryptophan, tyrosine, or phenylalanine. Store peptides in:

Amber glass vials (block UV)
Away from direct sunlight
In dark areas of the refrigerator

Moisture

Lyophilized peptides are hygroscopic — they absorb moisture from the air. Exposure to humidity can initiate hydrolysis and aggregation even in "dry" peptides. Keep sealed vials sealed. If you're using a multi-dose vial, minimize the number of times you pierce the septum (each puncture introduces a small amount of air and moisture).

Oxygen

Dissolved oxygen promotes oxidation. Some pharmaceutical peptide products are packaged under nitrogen or argon to displace oxygen from the headspace above the lyophilized powder.

How to Tell If a Peptide Has Degraded

Visual Signs

Color change: Most peptides should be white to off-white powder or clear to slightly opalescent solution. Yellowing, browning, or darkening suggests oxidation or Maillard-type reactions.
Cloudiness or particles in solution: May indicate aggregation or microbial contamination.
Failure to dissolve: If lyophilized peptide doesn't dissolve properly in the appropriate diluent, it may have aggregated or cross-linked during storage.
Unusual odor: Reconstituted peptide solutions should be nearly odorless (aside from a faint alcohol smell from bacteriostatic water). Strong or unusual odors suggest contamination.

Functional Signs

Reduced efficacy: If a peptide that was previously working well seems to have stopped working, degradation is a possible explanation (though tolerance and other factors should be considered — see our article on peptide tolerance).
Injection site reactions: Degraded peptides (particularly aggregated peptides) may cause more injection site irritation than fresh product.

Analytical Testing

The only definitive way to assess peptide quality is analytical testing:

HPLC can quantify remaining purity (percentage of intact peptide vs. degradation products)
Mass spectrometry can identify specific degradation products
These tests require a laboratory and aren't practical for consumers, but certificates of analysis from reputable suppliers provide this data for fresh product

Specific Peptide Stability Data

BPC-157

BPC-157 is remarkably stable compared to most peptides. Research shows it remains intact in human gastric juice for over 24 hours — an extreme acid environment that destroys most peptides within minutes [6]. This stability is one reason BPC-157 can be administered orally in research settings. In lyophilized form, BPC-157 stores well at -20°C for years. Reconstituted and refrigerated, 3-4 weeks with bacteriostatic water is a reasonable guideline.

Semaglutide

Semaglutide in its injectable pen form (Ozempic, Wegovy) has a 6-week in-use shelf life after first use, stored at room temperature below 30°C or refrigerated. Unopened pens are stable until the manufacturer's expiration date when refrigerated. The fatty acid modification (C18 acylation) that extends its half-life in the body also contributes to solution stability by improving solubility and reducing aggregation [7].

Insulin

Insulin analogs in opened pens/vials are stable for 28-42 days at room temperature (depending on the formulation). Unopened, they're stable for the labeled expiration date when refrigerated. Insulin is relatively fragile — heat, agitation, and light all accelerate degradation.

Growth Hormone Secretagogues

CJC-1295, ipamorelin, and GHRP-6 follow standard peptide stability patterns: stable for years lyophilized and frozen, 3-4 weeks reconstituted and refrigerated with bacteriostatic water.

Topical Peptides (Matrixyl, Argireline, GHK-Cu)

In commercial skincare formulations, stability depends heavily on the formulation matrix (pH, preservatives, emulsifiers, packaging). Professional formulations from reputable brands typically include stability testing data to support their shelf life claims. GHK-Cu in copper peptide serums is generally stable for 12+ months when stored away from light and heat.

Reconstitution and Post-Reconstitution Stability

How you reconstitute a peptide affects how long it lasts afterward:

Bacteriostatic water (BAC water) contains 0.9% benzyl alcohol, which inhibits bacterial and fungal growth. This is the preferred reconstitution diluent for multi-dose vials. Post-reconstitution shelf life: ~3-4 weeks refrigerated.

Sterile water (without preservative) has no antimicrobial protection. Once you puncture the vial, any introduced microorganisms can multiply. Post-reconstitution shelf life: ~7-14 days refrigerated. Single-use vials are ideal for sterile water reconstitution.

Normal saline (0.9% NaCl) is another option. It provides isotonicity (matching the salt concentration of body fluids) and can be used with or without preservative. Shelf life similar to the corresponding water type.

Key practices for maximizing reconstituted peptide life:

Swirl gently — don't shake or vortex (causes foaming, denaturation, and aggregation)
Refrigerate immediately after reconstitution
Use alcohol swabs on the vial septum before each withdrawal
Don't touch the needle to unsterile surfaces
Keep track of the reconstitution date (write it on the vial)
Discard if you see cloudiness, particles, color change, or unusual odor

Skincare Peptide Shelf Life

Topical peptide products are formulated differently from injectable peptides, and their stability rules differ:

Unopened: Follow the manufacturer's expiration date. Most are good for 1-3 years.
Opened: Most peptide serums have a PAO (Period After Opening) of 6-12 months, indicated by the open-jar symbol on packaging.
Pump dispensers vs. jars: Pump dispensers limit air and contamination exposure, extending functional shelf life. Jars expose the product to air and bacteria from fingers with each use — a peptide serum in a jar may degrade faster than the same formula in an airless pump.
Store in a cool, dark place. Bathroom cabinets get hot and humid. A bedroom shelf or the refrigerator is better for peptide skincare.

Frequently Asked Questions

Can I use a peptide past its expiration date?

For FDA-approved drugs (insulin, semaglutide), follow the manufacturer's expiration date — these are established through formal stability testing. For research peptides, lyophilized powder stored at -20°C is likely still good well past any stated "expiration," but potency may have decreased. Reconstituted peptides past the recommended use period should be discarded — the risk of both degradation and microbial contamination increases.

Does freezing reconstituted peptides extend their life?

Freezing can extend shelf life, but freeze-thaw cycles are damaging. Each freeze-thaw event causes ice crystals that can physically disrupt peptide structure and promote aggregation. If you freeze reconstituted peptide, divide it into single-use aliquots first so you only thaw what you need. Don't refreeze a thawed aliquot.

How should I store peptides during shipping?

Lyophilized peptides tolerate short shipping periods (1-3 days) at ambient temperature without significant degradation. Reconstituted peptides should be shipped with cold packs. In hot weather, request cold shipping or overnight delivery. Peptides that arrive hot to the touch should be assessed carefully.

Do peptide skincare products need refrigeration?

Most don't require it, but refrigeration won't hurt and may extend shelf life slightly. The exception is products formulated with oils or waxes that can solidify when refrigerated. Water-based peptide serums are excellent candidates for fridge storage. Check the manufacturer's guidance.

Can degraded peptides be harmful?

Degraded peptides are generally not toxic — they're fragments of amino acids, not dangerous chemicals. The primary risk is loss of efficacy (you're not getting what you paid for). A secondary risk is that degradation products or microbial contamination in old reconstituted solutions could cause injection site reactions or, rarely, infection. When in doubt, discard.

The Bottom Line

Peptides do expire, and how you store them matters more than most people realize. The practical rules are simple: keep lyophilized peptides frozen or refrigerated and sealed. Once reconstituted, use bacteriostatic water, refrigerate immediately, and plan to use the vial within 3-4 weeks. Track reconstitution dates. Don't chase false economy by using old, potentially degraded product.

For skincare peptides, store in a cool, dark place, prefer pump dispensers over jars, and replace products that have been open for more than a year.

The chemistry of peptide degradation is well-understood. The solutions are straightforward. A little attention to storage and handling ensures your peptides deliver what they promise.

References

Manning, M.C., et al. "Stability of protein pharmaceuticals: an update." Pharmaceutical Research 27.4 (2010): 544-575. PubMed.
Oliyai, C., and Borchardt, R.T. "Chemical pathways of peptide degradation." Pharmaceutical Research 10.1 (1993): 95-102. PubMed.
Torosantucci, R., et al. "Oxidation of therapeutic proteins and peptides: structural and biological consequences." Pharmaceutical Research 31.3 (2014): 541-553. PubMed.
Carpenter, J.F., et al. "Rational design of stable lyophilized protein formulations." Pharmaceutical Biotechnology 13 (2002): 109-133. PubMed.
Waterman, K.C., and Adami, R.C. "Accelerated aging: prediction of chemical stability of pharmaceuticals." International Journal of Pharmaceutics 293.1-2 (2005): 101-125. PubMed.
Seiwerth, S., et al. "Stable gastric pentadecapeptide BPC 157 and wound healing." Frontiers in Pharmacology 12 (2021): 627533. PMC.
Lau, J., et al. "Discovery of the once-weekly glucagon-like peptide-1 (GLP-1) analogue semaglutide." Journal of Medicinal Chemistry 58.18 (2015): 7370-7380. PubMed.

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