A Nanab Berry is part of the Berries family and can be used when trying to catch a Pokémon.
What does a Nanab Berry do?
Using a Nanab Berry when trying to catch a Pokémon slows its movements! This makes it easier to capture Pokémon that move fast and erratically. This is also helpful when trying to conserve Poké Balls, especially when low on inventory.
Where do I find Nanab Berries?
Nanab Berries are sometimes obtained when visiting PokéStops!
Level up reward
Nanab Berries are sometimes given as a level up reward in bulk quantity.
Trainers will not see this item until level 14. After reaching level 14, you receive some Nanab Berries as a level reward and will start to see them drop from PokéStops regularly.