How long do peptides last after reconstitution and in the fridge?

Peptides exist in three states with very different lifespans: sealed lyophilized powder, powder that has been mixed into solution, and solution that has been drawn into a syringe. Water is the enemy in all three, because the chemical reactions that break peptide bonds and oxidize side chains need it. Powder has almost none, which is why it lasts. Solution has nothing but, which is why the clock starts the moment you add water.

Freeze drying removes the water and leaves a stable cake of peptide, which is why vendors can ship powder across the world without ice. Stored in a freezer, away from light, most lyophilized peptides are expected to keep for a year or two with little loss, and the printed expiration on a reputable product reflects that. The fridge is nearly as good for anything you will open within a few months. Room temperature is survivable for the days a shipment takes but is not a storage plan, and a hot car or a sunny windowsill can do in an afternoon what months in the fridge would not.

Light matters more than people expect. Several amino acids, tryptophan, tyrosine and methionine among them, oxidize under UV, and clear glass vials offer no protection. Keep the box, or keep the vials in an opaque container inside the fridge. Moisture is the other quiet killer: a vial that has been opened and left with a loose stopper will pull water from the air and begin degrading as if it had been partly reconstituted.

GHK-Cu gives a visual check that most peptides do not. The powder should be a uniform blue; a vial that is colorless is likely plain GHK without the copper, or degraded. For everything else, powder that looks the same as it did on arrival is the only inspection available.

Once water goes in, the compound pages converge on the same instruction: fridge at 2 to 8 C, use within 4 weeks. That number comes from two places. Bacteriostatic water is labeled for 28 days after first puncture, and pharmacy compounding standards use 28 days as a common beyond-use date for multi-dose preparations. It is a conservative convention for the solvent and the sterility, not a measured stability figure for each peptide.

In practice, many peptides are chemically fine well past 4 weeks in the fridge. The site FAQ notes that BPC-157 and TB-500 are among the sturdier ones, and epithalon is described as relatively stable for a peptide. The reason the 4 week rule still holds is that every needle puncture is a chance to introduce bacteria, and the preservative's job gets harder with each one. A vial that has been punctured daily for six weeks is a sterility question before it is a potency question.

The way to make the rule painless is to reconstitute only what you will use in a month. A 10 mg vial of BPC-157 at 500 mcg a day is 20 days of doses, which fits. A 50 mg vial of GHK-Cu at 1 mg a day is 50 days, which does not, and the better move is to reconstitute half or accept that the last stretch may be weaker. The calculator shows how many doses a given vial and concentration yields.

A few compounds come with shorter windows on their own pages. IGF-1 LR3 is listed at 2 to 4 weeks with a warning to handle gently and never shake; it is a larger, folded protein and mechanical stress unfolds it. NAD+ degrades in solution faster than most peptides and should stay clear and colorless. HGH is a 191 amino acid protein and product labels run from 2 to 4 weeks depending on brand. GHK-Cu should keep its blue color; cloudiness or fading means discard.

Nasal sprays of Semax and Selank degrade faster once opened, partly because a spray bottle is opened to air with every use. Cheap ready-made sprays of unknown age may be nearly inert by the time they arrive. The GLP-1 drugs have a different rule: compounded semaglutide and tirzepatide are stable for the usual 4 weeks in the fridge, but must not be frozen once mixed, and branded pens are labeled to tolerate up to 21 days at room temperature if needed.

Bacteriostatic water is sterile water with 0.9 percent benzyl alcohol, and the benzyl alcohol stops bacteria from multiplying in a vial that gets punctured repeatedly. That is the entire job. It does not slow hydrolysis, oxidation or aggregation, the chemical processes that actually reduce potency over time, and a peptide in bacteriostatic water degrades at the same rate as one in sterile water. What changes is that the bacteriostatic vial stays safe to inject for weeks while the sterile water vial is a single use product.

An opened vial of bacteriostatic water is itself labeled for 28 days, which is a second reason the 4 week convention exists. Bacteriostatic water vs sterile water goes through the differences, the allergy note and which compounds specify sterile water instead.

Most degradation is invisible. A solution can lose a third of its potency and look identical, which is why dates matter more than inspection. Still, some changes are visible and all of them mean discard.

Powder travels well. A sealed lyophilized vial in a dark bag survives a week at room temperature with negligible loss, which is how vendors ship it in the first place. Solution travels badly. A reconstituted vial needs an insulated pouch with a cold pack and should go back into a fridge at the destination; a day or two cool is fine, a week warm is not. For a short trip, drawing the doses you need into syringes and keeping them cold is reasonable for a day, but pre-filling a week of syringes leaves peptide sitting against plastic and rubber for far longer than it should.

Freezing a reconstituted vial is the mistake people make trying to extend its life. Ice crystals and the concentration changes that happen as water freezes out of solution unfold and aggregate peptides, and each freeze thaw cycle does more damage. The reconstitution guide and every compound page say the same thing: fridge only once mixed. If you want to store peptide for longer than a month, store it as powder. Some people aliquot a large vial into several smaller sterile vials at reconstitution and freeze those once each, which is a lab practice that works if the aliquots are never thawed and refrozen; it is more handling than most need.

Almost always weaker. When a peptide degrades, the main products are shorter fragments of the same chain and oxidized versions of the same molecule, which are inert rather than toxic. A six month old reconstituted vial of BPC-157 that was kept cold and dark is most likely a less concentrated vial of BPC-157, not a poison. The practical consequence is that you cannot know how much you are dosing, which matters a lot for compounds with narrow ranges and very little for ones used at the bottom of a wide range.

The exception is contamination, and that is a function of handling rather than age. A vial punctured many times, with a reused needle, or left out of the fridge, can grow bacteria that the benzyl alcohol cannot keep up with, and injecting that causes abscesses or worse. So the rule separates into two parts: an old vial that was always sealed and cold is a potency question, and an old vial with a long puncture history is a sterility question. The first is a judgment call. The second is a discard.