A Pokémon holding this item gains 4 HP EVs whenever it gains experience in battle (EVs are awarded for each Pokémon knocked out in Horde Battles despite experience being gained all at once); its effect is doubled by Pokérus. (In Generation IV, level 100 Pokémon cannot gain EVs in battle; from Generation V onward, they gain EVs whenever they would earn experience.)
The Speed stat of the Pokémon holding this item is halved during battle.
A Pokémon holding this item now gains 8 HP EVs instead of 4 whenever it gains experience in battle.
Outside of battle
From Pokémon HeartGold and SoulSilver onward, if this item is held by a parent when breeding at Pokémon Day Care or a Pokémon Nursery, the HP IV of a parent holding a Power Weight will always be passed down to the child. If both parents hold a Power Weight, one parent will be selected at random to pass down its HP IV.
||A Pokémon hold item that promotes HP gain on leveling, but reduces the Speed stat.
|A Pokémon held item that promotes HP gain on leveling, but reduces the Speed stat.
|An item to be held by a Pokémon. It reduces Speed but allows the holder's maximum HP to grow more after battling.
||An item to be held by a Pokémon. It reduces Speed but allows the holder's max HP to grow more after battling.