Great Fairy's Tears

From Zelda Wiki.org

In Twilight Princess, Great Fairy's Tears is a bottled item. When used, not only does it restore full health, but also temporarily doubles the sword's attack strength. Its function is similar to the Elixir Soup from The Wind Waker, but unlike the soup, a bottle of these tears only holds one serving.

The method of earning Great Fairy's Tears is significantly harder than the Elixir Soup, as only one bottle is given to you by Jovani after capturing 20 Poe Souls. After this, he'll say you can get more in the Gerudo Desert - what he actually refers to is the Cave of Ordeals, where Great Fairy's Tears are the reward after surviving fifty monster-filled rooms. Clearing the cave also releases Great Fairies to each of the Light Spirits' springs around Hyrule, who can then be talked to to receive new Great Fairy's Tears.

Link can only have one bottle of these tears at once. Since another bottle can be obtained from a Great Fairy immediately after using one, it's a viable strategy to drink it right away to get the double power effect immediately, and then obtain another bottle to use later.