Saradomin brew is made by mixing toadflax and a crushed bird's nest in a vial of water, giving 180 Herblore experience. It requires level 81 Herblore. It is slighly lighter in colour than a normal strength potion.
Saradomin brew temporarily raises your Hitpoints by 15% (since it is a potion this means it is one of few ways to raise your Hitpoints above the normal maximum) and your Defence by 25% (better than a super defence potion). It also temporarily lowers your Strength, Attack, Magic and Ranged by 10% though.
They heal the highest Hitpoints per inventory spot(if not counting purple sweets, which can be stacked for infinite health), and so, are often used in conjunction with Super restore potions in places such as in the TzHaar Fight Cave while attempting to obtain a Fire cape, high-leveled Bounty Hunting, or in Barrows runs, to decrease the number of bank trips required.