Red Potion is an reoccurring item in The Legend of Zelda series. It has the ability of healing Link's hearts. It may be obtained by a potion shop or by making it out of Chu Jelly on Windfall Island. By killing an enemy like a Chu in The Wind Waker you can obtain Chu Jelly.
The Legend of Zelda
In The Legend of Zelda, red potion can be obtained by giving the letter from the old man to the old lady who sells potions. You can buy red potion for 68 Rupees. The red potion heals all your hearts and can be used twice. When red potion is used once, it turns into Blue Potion that heals all your hearts but only can be used once. When you use all the red potion up the Bottle disappears.
A Link to the past
Ocarina of time