Hydra

 is a consumable item in Fallout: New Vegas.

Background
Hydra is a drug developed from the basis of Antivenom, due to the Legion's disapproval of using modern medicine, some Legionaires attempted to develop a different means to help them heal damaged limbs. To do that, they combined cave fungus with antivenom. Developing a curative agent called Hydra which acts as a painkiller and restorative for Limbs, the drug has since then been widely used throughout the entire Mojave Wasteland.

Characteristics
Like a Doctor's bag, Hydra is used to restore health to crippled limbs making it especially useful in Hardcore mode where stimpaks or sleeping in a bed you don't own (from having rented or being given the room) won't heal these injuries. It has the advantage over Doctor's Bags in that it is weightless and it will continue to slowly heal the crippled wounds over 60 seconds. In a tough fight where you might receive crippling wounds several times a single dose of Hydra can heal them as you receive them. Hydra also benefits from the Chemist and Day Tripper perks.

The down side is that Hydra carries a 10% risk of Addiction. If this happens you'll suffer a negative hit to your statistics (-3 Endurance) unless you either use more Hydra or Fixer (to provide temporary relief from the symptoms of withdrawal) or have a doctor cure you.

Hydra can be crafted at a campfire with a Survival skill of 75 and 1 x Cave fungus, 2 x Night Stalker blood and 1 x Radscorpion poison gland. In the base game, the recipe requires five Cave funguses, and the resource is extremely rare with no available harvest locations and only Legion soldiers occasionally carrying some as loot. Patch 1.2.0.31x significantly increased Cave fungus drop rates, especially on Legionary scouts, and changed the required amount of Cave fungus in the recipe to only one. The Honest Hearts add-on includes many caves in Zion Canyon that are abundant with Cave fungus.

This makes the only reliable source present in all versions of the game Jack, one of the drug dealers working at the Red Rock Drug Lab. If your Survival is high enough to make the drug yourself and you have a positive reputation with the Khans you can teach him the recipe for Hydra and he'll begin stocking it for sale.

Locations

 * You can teach Jack at the Red Rock Drug Lab how to make this chem with a Survival check of 75, and he will then stock it for sale at his shop.
 * There are two doses on a desk at the Nevada Highway Patrol station.
 * Sometimes found on dead Powder gangers.

Behind the scenes
Most likely named after the mythological creature, the Hydra, which was capable of regrowing its head when severed.

Гидра