Mushroom Tea is a drink in Mario & Luigi: Bowser's Inside Story and Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey. There are three variations of Mushroom Tea: Regular, Milk, and Royal.
Milk Mushroom Tea can also be bought at the Tea Counter, but for eight coins. This tea will restore all lost SP.
Royal Mushroom Tea can be bought at the Tea Kiosk for ten coins, or obtained for free at the Star Shop. This tea will fully restore both HP and SP. A similar drink can be obtained from the orange Emoglobins in Bowser's body, while Bowser himself has an equivalent with Negative Ions from Shop Blocks.