Potion - Pokémon Rulings Compendium

When using Potion, can I choose to heal less than 30 damage from my Pokemon?: If the Pokemon has 30 or more damage on it you must heal 30 damage, but if it has less than 30 damage you do as much as you can and heal all of it.

Source: TPCi Rules Team (2017-05-18)

The wording of Potion now heals 30 damage from 1 of your Pokémon instead of 20 damage.

Source: TPCi Announcement (2011-04-11), PUI Rules Team (2011-05-05)