Which Pokémon games first introduced held items that Pokémon could carry in battle?

Pokémon Gold and Silver first introduced held items that Pokémon could carry in battle.

Released for the Game Boy Color, Gold and Silver expanded the mechanics of the original games with a real-time clock, a day-and-night cycle, breeding, new types, and Pokémon that could hold items. Held items gave battles another layer of strategy because an item could restore health, cure a status condition, or strengthen a Pokémon.

Berries were among the new held-item mechanics. A Pokémon could carry a Berry and use it automatically under certain conditions, while other items produced different battle effects. The games also introduced the Pokégear and added 100 new Pokémon from the Johto region.

Held items are not the same as ordinary inventory items used directly by the Trainer. That distinction is why Gold and Silver are credited with introducing the mechanic: the Pokémon itself carries the item and can trigger its effect during play.