If the Pokémon is holding a Berry to be eaten when its HP drops to 1/4 or less of its max, it will instead eat the Berry when its HP drops to 1/2 or less of its max.
Gluttony causes the Pokémon to eat Berries that would normally be eaten at 25% HP or lower to be eaten at 50% HP or lower instead. It has no effect on Berries that activate at other HP thresholds (such as the Oran Berry, which is normally eaten at 50% HP or less) or Berries with non-HP-related trigger conditions (such as the Leppa Berry and Lum Berry).
Please note that Abilities marked with a superscript are only available in the stated generation or later.
For Generation III and IV games, ignore Hidden Abilities.
In other games
Pokémon Mystery Dungeon
In the Explorers series and WiiWare games, Gluttony causes the Belly of the Pokémon with this Ability to empty out twice as fast. However, it also grants both benefits of the Survivalist IQ skill: a 50% chance to consume Grimy Food with no ill effects and 10% more Belly gain from food consumption.
From Gates to Infinity onward, Gluttony heals 25 HP when the Pokémon eats or drinks an item.
In Pokémon UNITE, Gluttony is Snorlax's Ability. It increases the effects gained from eating Berries and increases movement speed by 25% while moving towards Berries.