
Pimento bitters are a spice-forward cocktail bittering agent flavored predominantly with allspice berry.
A dash or two adds a warm, baking-spice accent of allspice. Use it sparingly, so the spice shows without turning the drink bitter.
Bittermens Elemakule Tiki
The closest swap, use dash for dash.
Angostura
The easiest fallback option, also dash for dash. It adds a general spice note without a clear allspice flavor.
Pimento dram
This sweet rum liqueur works too. Start with half a barspoon per dash and adjust to taste.
Pimiento pepper
Won't work. The sweet red pepper used to stuff olives has nothing to do with allspice.
Allspice owes its aroma to eugenol, the compound that makes clove smell of clove, and eugenol is stable and slow to fade. Closed and out of the sun, the bottle stays sharp for years.