Shamrock is a cold tea, lemon, and Jamaica-rum drink served over ice.
Louis' Mixed Drinks with Hints for the Care & Serving of Wines by Louis Muckensturm (1906, p.101)
| 1 slice | lemon — Lemon slice | acid |
| 2 dashes | lemon juice — Lemon juice | acid |
| 0.5 bar-glass | Jamaica rum | base |
| 1 cup | tea — Strong cold tea | base |
| 1 piece | ice — Ice | other |
Ice: Ice
The Artistry of Mixing Drinks by Frank Meier (1936, p.39)
| 0.25 part | Green Chartreuse | base |
| 0.5 part | Irish whiskey — Irish Whiskey | base |
| 0.25 part | dry vermouth — French Vermouth | modifier |
Café Royal Cocktail Book by W. J. Tarling (1937, p.191)
| 3 dashes | creme de menthe — Green Crème de Menthe | base |
| 0.5 part | Irish whiskey — Irish Whisky | base |
| 3 dashes | Chartreuse — Green Chartreuse | modifier |
| 0.5 part | dry vermouth — French Vermouth | modifier |