From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Senzu (仙豆, Senzu; FUNimation "Senzu Bean"; Literally meaning "Holy Bean") are a kind of mystical bean with immense rejuvenating properties in the Dragon Ball manga and anime. Senzu are grown by Karin at Karin Tower. When eaten, the consumer's energy and physical health are restored to their fullest. Their texture is said to be a cross between an uncooked (or under-ripe) bean and a celery stalk. Karin stated that one bean could keep a person full for ten days, though some who had eaten the Senzu became hungry sooner due to their naturally larger appetite (namely Saiyans as they generally eat much larger amounts of food). It had been seen that eating too many Senzu at a time was dangerous as when they were first introduced, Yajirobe was flabbergasted that the only thing Karin had to eat were "beans", and so he ate a few handfuls of Senzu which resulted in him comically gaining about a pound for every handful he had eaten. Since Karin allied himself with Son Goku and his friends, Karin usually assisted them by providing the Z Warriors with a sack of Senzu whenever possible as it took time to grow just a single Senzu.
The Senzu's healing capabilities have been able to perform such feats as healing Yamucha's impaled torso after an encounter with Doctor Gero and Artificial Human No. 19 and restoring fatally injured characters to perfect health on various occasions. One significant example of the power of Senzu is demonstrated early during the Namek Saga when, after his face-off with Vegeta, Goku spent seven episodes at Wukong Hospital never traveling far from his bed (although this was mostly at the advice of Chichi and the orderlies), the only exception being his premature escape in "Hunt for a Dragon Ball" which rendered him powerless once again. When Goku eats a Senzu Yajirobe gives him, he is instantly revitalized in spite of these seven episodes spent naturally recovering with medical assistance. The best example is during the Namek Saga when Goku gives a Senzu to Gohan who had a broken neck and was almost dead. It appears, however, that Senzu cannot heal injuries that have already healed over, such as Tenshinhan's and Yamucha's scars or Saiyan tails, or cure ailments, such as Goku's Heart Virus contracted during the Androids Saga.
Goku's good nature has led him to give Senzu to battered enemies after fights. Examples of this include Piccolo, Vegeta, and Cell (though the latter was more to make the fight fair than an actual act of goodwill, as Cell was about to face Gohan while he had notquite recovered to full strength).
In the Budokai video game series and Dragon Ball Z: Burst Limit, Senzu can be used to heal a character. In the Budokai video game series, they restore a character's health and Ki fully. In Burst Limit, they are a drama piece that will usually heal about one bar of health. In the Budokai Tenkaichi video game series, Yajirobe can eat a Senzu as one of his Blast 1 attacks in order to gain full health.
- Senzu are based on Lima Beans.
- They are named Lima Beans in the Harmony Gold dub.
- Yajirobe states in "The Victor" that Senzu taste like Fish.
- They were last seen during the Majin Buu Saga when Majin Vegeta knocks Goku out and eats the last one he has left, right before flying off to face Majin Boo.
- You can acquire items such as Small Bean, Medium Bean, and Large Bean in Dragon Ball Z: Attack of the Saiyans that are in fact Senzu, but they do not replenish health completely as in the series. A Small Bean restores your health a little bit, a Medium Bean does a little more, and a Large Bean does the most.
- Vegeta states during the Cell Saga that he hates eating Senzu.
- "Sacred Water"
Karin: "It's a Senzu Bean – magical. Just one will keep you full for at least ten days, but, uh, you have to eat it first."