
Lemon-lime soda is a clear, sweet carbonated soft drink flavored with lemon and lime.
A substitute has to cover all three jobs or the drink needs building differently. Brands differ more than the category suggests, mostly in acidity, so taste before you scale a batch.
Lemonade (British and Australian usage)
The nearest local equivalent rather than the same drink: British lemonade is lemon-flavored rather than lemon-lime and usually softer in acid, though the Australian version is blended from both oils. In North America lemonade is a still lemon drink, so a recipe’s origin decides which one it means.
Bitter lemon
Lemon soda with quinine, so it carries a bitterness this does not: it substitutes when a drink wants the bitterness and ruins one that wanted plain sweetness.
Sealed, cold, and used soon after opening. A big bottle left open overnight is noticeably flat by morning; drinkers register a soda as flat after it loses only about 15% of its gas. Flat soda in a highball leaves the drink both sweet and dead.