How Long Does Glutathione Last? Powder and Mixed Storage

Lyophilised glutathione keeps at 2 to 8 °C for the weeks a vial is in use and at minus 20 °C for months. Mixed with bacteriostatic water, it falls under Vistara Labs’ general handling guidance of 8 to 12 weeks in the fridge, with quality fading from around week 6 to 8, and for glutathione the cold is not optional. Unlike most compounds in the catalogue, glutathione has measured figures for this: in one set of solution data it lost about 10% within three weeks at room temperature and showed no measurable loss over four months at 5 °C. The reaction behind that loss is oxidation to GSSG, and it cannot be seen.

Findings

• Reduced glutathione (GSH) is a tripeptide with a free thiol group; in water, two molecules join through that thiol to form oxidised glutathione, GSSG.
• A laboratory supplier’s guidance states that aqueous solutions readily oxidise in air to GSSG, and that a chelating agent lengthens the half-life of the reduced form.
• In patent stability data, a pH 6.4 solution at room temperature lost 10 to 12% of its reduced glutathione per month, reaching 90% within three weeks (2004).
• The same filing reports that at 5 °C the concentration showed no decrease, within experimental error, over 112 days (2004).

Why glutathione behaves differently

Glutathione is a three-residue peptide of glutamate, cysteine and glycine, and the cysteine’s thiol group is what makes it an antioxidant. It is also what makes it unstable in water. Two reduced glutathione molecules give up their thiol hydrogens and link through a disulfide bond to become GSSG. Sigma-Aldrich’s product guidance states that aqueous solutions of reduced glutathione readily oxidise in air to GSSG, recommends fresh solutions for that reason, and notes that a chelating agent increases the half-life of the reduced form (Sigma-Aldrich, product G6529). The chelator point matters because metal ions are part of the chemistry: a 2004 patent on glutathione storage describes the oxidation as catalysed by molecular oxygen and by metal ions such as Fe3+, while still proceeding slowly without them (Harbin and Stephens, US Patent 6,835,811, 2004).

Most peptides in the catalogue are limited by reactions such as deamidation or hydrolysis. Glutathione’s main route is different: it depends directly on temperature and on how much air reaches the solution. Every time a stopper is pierced, a little air enters the headspace, which is why a large vial accessed many times is the hardest case.

What do the numbers show?

The clearest figures come from that patent, filed by Kromar Medical. The applicants report that reduced glutathione in water frequently loses 10 to 15% of its initial concentration per month. In their comparative example, a solution of 180 mg/mL at pH 6.4 held at room temperature lost 10 to 12% per month and fell to 90% of its starting value within three weeks. In the main example, a matching solution of 189 mg/mL at 5 °C showed no decrease within experimental error across 112 days, with measured ratios of about 0.98 to 1.02 of the starting concentration. The claims cover storage above the solution’s freezing point and below 15 °C (Harbin and Stephens, US Patent 6,835,811, 2004). These are an applicant’s data in a patent, not a peer-reviewed study, and the solution contained a small amount of an added salt, but the direction is unambiguous: cold almost stops the reaction and room temperature does not.

That is why glutathione sits within the general 8 to 12 week window only when it is kept at 2 to 8 °C without breaks.

How long does glutathione powder last?

Dry, the thiol has no water to react in, and the sealed vial holds for the weeks it is in use at 2 to 8 °C and for months at minus 20 °C, in its box. A cold vial warms to room temperature before opening so moisture does not condense on the cake. A few days at ambient temperature in transit do not harm it.

How long does glutathione last after mixing?

Condition	Glutathione
Lyophilised, sealed, 2 to 8 °C	The weeks the vial is in use
Lyophilised, sealed, minus 20 °C	Months
Mixed with bacteriostatic water, 2 to 8 °C	8 to 12 weeks (general guidance), fading from around week 6 to 8
Mixed, room temperature	About 10% lost within three weeks in patent data
Mixed, frozen for repeat access	No; single-use aliquots frozen once only

The USP General Chapter 797 figure of 28 days for a preserved multi-dose container is a sterility rule, separate from oxidation. Volumes for the 600 mg and 1500 mg vials, with a calculator, are on the glutathione reconstitution page.

How can you tell glutathione has degraded?

This is the compound where appearance helps least. Reduced glutathione and GSSG are both colourless in solution, so a vial can lose a meaningful share of its reduced form and still look perfect. The mixing date and an unbroken record of cold storage are the real quality check. Discard the solution if it shows:

• Cloudiness that does not clear, or particles.
• A yellow tint.
• Time at room temperature beyond brief handling, which the patent data show is when loss accelerates.
• A freeze-thaw cycle.

More on haze: why peptides gel or go cloudy.

Travelling with glutathione

Sealed vials tolerate a few days at ambient temperature, away from heat. A mixed vial is the case where keeping it cold on the move matters most, given the room-temperature figures above; the peptide travel case is made for that. Orders ship from within Canada by Canada Post Xpresspost.

Is there a glutathione nasal spray?

Not from Vistara Labs. Glutathione is supplied as lyophilised vials only, mixed with bacteriostatic water. The ready-mixed sprays are listed in peptide nasal sprays in Canada.

Frequently asked questions

How long does glutathione last in the fridge?

Mixed with bacteriostatic water and kept at 2 to 8 °C, glutathione falls under Vistara Labs’ general guidance of 8 to 12 weeks, with quality fading from around week 6 to 8. Patent data recorded no measurable loss over 112 days at 5 °C.

How long does glutathione last at room temperature?

Sealed powder tolerates a few days. In solution it oxidises: patent data recorded a loss of 10 to 12% per month at room temperature, reaching 90% of the starting amount within three weeks.

Can you freeze glutathione?

Sealed powder can be held at minus 20 °C for months. A mixed vial that will be opened again is not frozen and thawed; laboratories freeze single-use aliquots once. The patent’s claimed storage range was above freezing and below 15 °C.

Does glutathione go bad?

Yes. In water its reduced form oxidises to GSSG, driven by air, metal ions and warmth. Both forms are colourless, so the change cannot be seen; storage history is the guide.

What is GSSG?

GSSG is oxidised glutathione: two glutathione molecules joined by a disulfide bond between their cysteine thiols. It is the main product when reduced glutathione is left in solution with air.

Handling windows: Vistara Labs, October 2026. Sources: Harbin R, Stephens L. Extended storage of reduced glutathione solutions. US Patent 6,835,811 B1, issued 28 December 2004 (Kromar Medical Corp). Google Patents. Sigma-Aldrich. L-Glutathione reduced, product G6529, product FAQ. sigmaaldrich.com. USP General Chapter 797, beyond-use dating.

More on this: How Long Do Peptides Last After Mixing?, Glutathione: the research behind the antioxidant and Buy Glutathione in Canada.