Poison Resistance

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“Reduces poison damage by this amount.”— Fallout game description

Poison Resistance is derived statistic in Fallout, Fallout 2, Fallout 3, Fallout 4, Fallout 76, Fallout: New Vegas and Fallout Tactics.

This statistic reduces poison damage by a percentage as well as the chance to get poisoned. In Fallout 3 and Fallout: New Vegas, this statistic is hidden.

Fallout, Fallout 2, Fallout Tactics

{\text{Initial Level}}={\text{Endurance}}\times 5

The Fast Metabolism trait sets initial poison resistance to 0.
The Snakeater perk increases poison resistance by 25% per rank.
The Vault City Inoculations perk increases poison resistance by 10%.

Notes

The average NPC has a 25% poison resistance.
In Fallout, Poison Resistance capped at 100%, although it cannot be raised past 75%.
In Fallout 2, it is capped at 95%.

Fallout 3

Poison Resistance is also present in Fallout 3. It has a much smaller part than in the previous games since only a few enemies (Radscorpions chief among them) use poison, and poison effects tend to be weak.

{\text{Initial Level}}\%=({\text{Endurance}}-1)\times 5

Example: A starting Endurance of 5.

(5-1)\times 5=20\%~{\text{Poison resistance}}

The Cyborg perk can increase resistance by +10%.
The Survival Expert perk can add between an additional +2% to +6%.

Fallout: New Vegas

Fallout: New Vegas uses the same equation as Fallout 3, but Poison Resistance has much more use: there are cazadores, bark scorpions, night stalkers, and weapon poisons, all in addition to radscorpions. In Lonesome Road, there are also venomous tunnelers. Moreover, poison in Fallout: New Vegas is generally much more lethal.

Honest Hearts perks

Tribal Wisdom increases the poison resistance by 25%.

Old World Blues perks

Mile in Their Shoes - after consuming the nightstalker squeezin's, poison resistance is increased by 5%.
Cardiac Arrest increases poison resistance by 50%.
Heartless makes the player character immune to poisoning.

Items and consumables

Gecko-backed leather armor, Gecko-backed metal armor and variants (+15)
Wasteland tequila (+5, affected by survival) and Large wasteland tequila
Snakebite tourniquet cures poison and +85 resistance (30s)
Antivenom, Datura antivenom and Fiery purgative cure poisoning.
Hazmat suit (+85 resistance)
Blood Shield (+50 up to +85 depending on the player character's Medicine)

Fallout 4

Poison Resistance is not a derived statistic in Fallout 4. Acquiring it is only possible via three methods:

Astoundingly Awesome Tales #5: Grants +5 Poison Resistance.
Legendary Armor pieces with the Poisoner's modifier: Grants +25 Poison Resistance. A maximum of 5 pieces can be worn at once, totaling +125 Poison Resistance
Med-X: Temporarily provides +250 Poison Resistance
Tunnel Snakes outfit: Grants +10 Poison Resistance.

Only a handful of enemies deal poison damage, such as the mirelurk queen and bloodbugs.

Fallout 76

Poison Resistance is not a derived statistic in Fallout 76 as it can be directly influenced by the player; it is not derived from any other statistic and is not a function of any other value. Players can modify their own Poison Resistance in the same manner as other resistances, through armor, perk cards, or consumables. Poison damage comes from a small variety of enemies and weapons, such as the scorchbeast queen and Bug grenade.