minus 80 °C is colder than anything a lyophilised cake needs. 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. A dry cake has no solvent to react in, so the marginal benefit below a domestic freezer is small and the marginal risk is not: freeze-thaw on the way in and out, and condensation on a cold stopper when you open it, are the failure modes that actually happen at minus 80 °C. Nothing here is medical advice, and research-use-only material is not approved for human use.
More usefully, this is the tag where the advice is cheapest to follow and most often ignored.
Store with the desiccant sachet if one was supplied, inside the secondary container rather than loose in a drawer. Residual moisture is the dominant variable in solid-state stability.
Lyophilised powder: refrigerated at two to eight degrees for months, frozen at minus twenty for longer. The gain from minus eighty over minus twenty is small for a dry solid and is not usually worth the arrangement.
Residual moisture is the dominant determinant of solid-state stability, which is why desiccants accompany lyophilised material.
Nothing here is medical advice, and research-use compounds are not approved for human use.
Minus eighty buys very little over minus twenty for a dry solid.