Is there any published stability data for retatrutide at minus 80 °C?

Stated plainly: retatrutide · minus 80 °C.

This is asserted often enough that I assumed it was established, and then I went looking for the source.

I have searched the primary literature and found one paper that is adjacent but not on point.

Can anyone point me at a primary source, or confirm that there is not one?

Probably not at minus 80 °C specifically, because that is not where stability programmes take their readings. Accelerated work is conventionally run at 25 °C and 40 °C, with the refrigerated condition as the control, so minus 80 °C sits between or beyond the published points and what you will find is bracketing rather than a measurement. minus 80 °C is 85 kelvin below a refrigerator, and below the glass transition of a lyophilised cake the ten-degree rule of thumb stops applying at all — solid-state chemistry is not slow liquid chemistry, it is a different regime, and the failure modes that survive it are mechanical rather than chemical. Whatever you find, check what was measured before you use it: a paper reporting purity at minus 80 °C has not measured content, and the two fail at different rates for different reasons.

On the detail: aggregation is a physical process and is the one most often caused by handling rather than by time.

Aggregation is physical: peptides unfold at air-liquid interfaces and associate. Shaking maximises that interface, which is why swirling and shaking produce visibly different outcomes on the same vial.

Deamidation converts asparagine or glutamine to the corresponding acid via a succinimide intermediate, adding one dalton. It is base-catalysed, accelerates above neutral pH and is the dominant aqueous pathway for many peptides.

Swirl, never shake. Aggregation is a handling problem more than a time problem.

edited 24 Jul 2026 by triple_agonist_q — updated for the 2026 guidance change

The honest answer is that most reported "degradation" is adsorption and dilution error rather than chemistry.

Adsorption onto glass and plastic is significant at low concentrations — micrograms per millilitre — and negligible at milligrams per millilitre. It is the usual explanation for an apparent loss in a dilute preparation.

Freeze-thaw cycling drives aggregation through concentration at the ice interface and pH shifts as buffer components crystallise out at different rates. Each cycle costs something.

Aggregation at air-liquid interfaces is established from surface-tension and particle-count studies and is the basis for anti-agitation handling guidance.

Nothing here is medical advice, and research-use compounds are not approved for human use.

Sequence decides which pathways are even available. Check the residues.

edited 4 Jul 2026 by tyndall_haze — tightened the wording; no substantive change

Start with the sequence, because which pathways are available depends on which residues are present.

A mass spectrum resolves most of this: minus eighteen is dehydration or succinimide, plus one is deamidation, plus sixteen is oxidation, and an unchanged mass with a shifted retention time is an isomer.

Hydrolysis cleaves the backbone, most readily at aspartate-proline and aspartate-glycine sequences, and is acid-catalysed. In a dry solid it barely proceeds at all.

Adsorption losses at low concentrations are quantified in formulation studies and are the reason carrier proteins are used in dilute preparations.

Apparent loss in a dilute preparation is usually adsorption rather than degradation and is worth ruling out first.

A mass spectrum names the pathway. Plus one, plus sixteen, minus eighteen.

Answer first: the degradation pathways worth knowing are hydrolysis, deamidation, oxidation, aggregation and adsorption, and each has a different trigger and a different mitigation.

Oxidation targets methionine, cysteine and tryptophan, adding sixteen daltons per oxygen. It is catalysed by trace metals and promoted by dissolved oxygen and by light.

Metal-catalysed oxidation of methionine is documented across peptide and protein formulations and is why chelators appear in some formulations.

Cold, dry, dark, still. Those four words cover most of the mitigation.

This is answerable from the chemistry rather than from anecdote, which is unusual and welcome.

Light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations.

Deamidation via the succinimide intermediate is well characterised, with sequence-dependent rates highest for asparagine-glycine motifs.

The caveat is that none of these pathways can be seen by looking at a vial, and a clear solution can be substantially degraded.

At dilute concentrations, suspect adsorption before you suspect chemistry.