From Brotato Wiki
+3 HP Regeneration
Item
Regeneration Potion is an in-game item that can be bought from a Shop or can be found in a Crate. Most Items modify the Stats of the player, and some of them provide additional effects.
Unique
Regeneration Potion is a unique item. Only 1 of each unique item can be equipped, and it will then no longer be offered in the Shop, and no longer drop from loot crates.
Notes
The Regeneration Potion gives you a special ability to double your HP Regeneration when you are below half of your Max HP.
The Regeneration Potion makes your HP Regeneration heal +2 HP per tick of healing, rather than doubling the rate of ticks.
The Regeneration Potion is a very powerful item on builds that relies on HP Regeneration for healing, commonly seen on characters such as Bull, Doctor, Lich, or Masochist