Hydra

 is a consumable item in Fallout: New Vegas.

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 won't heal these injuries. It has the advantage over Doctor's Bag's 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.

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 or have a doctor cure you.

Hydra can be crafted at a camp fire with 75 Survival skill and 1 x Cave fungus, 2 x Night Stalker blood and 1 x Radscorpion poison gland. Cave fungus is extremely rare in the game with no available harvest locations and only Legion soldiers occasionally carrying some as loot. (Patch 1.02 significantly increased Cave Fungus drop rates, esspecially on Legionary scouts.)

This makes the only reliable source 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.