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Jet is the most recognizable drug in theFalloutuniverse. It gives the players that inhale it combat bonuses, but it also has addicting properties that can become a hindrance. Since its introduction in Fallout 2, the drug has been in every iteration of the franchise, but how it came to be is slightly confusing.
Many characters are addicted to Jet, to the point where a counterdrug had to be created before what little civilization existed on the wasteland could endure, but how did it come to be? Why is the drug so powerful, and why is it closely related to cattle dung?

What Is Jet?
While Jet is described as a recreational drug by many characters,players can use it to enhance their charactersin a number of ways for a short period of time. Exactly how they are improved depends on the game, but it often involves improved performance when it comes to combat.
It is also extremely addictive, and even player characters can beafflicted with withdrawalif they end up taking any form of Jet.These effects are often temporary, except in Fallout 2, where Jet is a key element of the plot, and finding a cure is a complicated process.

Effect
Fallout 2
Enhances strength, perception and adds bonus action points for 5 minutes.
Change one die roll into one of your choice.
Creating Jet
The main component of Jet is the fumes fromBrahmin waste, but inhaling it like that just gives a slight high.A skilled chemist can create Jet from those fumes, hence why Jet is often inhaled, but it can also be administered in other ways.
Brahmin are mutated cattle that roam the wasteland in all games. Their main feature, other than their involvement in making Jet, is that they have two heads.

Plenty of drug cartels throughout the wastelandhave places dedicated to creating the drug, since its addictive nature and ease of production have led it to replace other addictive chemicals that were around before the Great War.Many variants have been createdto increase its effect, and these variants include:
One final variant of Jet is Dixon’s Jet, although the lack of skill of Dixon makes it a lesser version of the drug.

The Origin Of Jet
Chronologically speaking,Jet is mentioned everywhere in the lore, and it is possible iteven appeared in the Fallout TV Show. But the first time we asplayers heard about the chem was in Fallout 2, and it was introduced bythe Mordino crime family around 2241.
Myron, a teenage chemistemployed by the Mordino family,discovered Jet while trying to create a highly addictive drugbased on mushrooms.He was using Brahmin wasteas fertilizer for the mushrooms, but the people cultivating the product were already getting high from the fumes of the dung alone.

It seems thatthe first cattle to become Brahmin were fed artificially enhanced protein, which was meant for human consumption butended up contaminated.This is likely what led to the Brahmin that we know today, and that contaminated chemical is what they release when they defecate.
You can also theoretically make Jet from Brahmin blood, but using their waste is a much easier process.
Since future entries in the franchise have Jet appearing in name and function even before the Great War, we have to assume thatMyron was lying about discovering Jet.There is a small piece of optional dialogue where it is implied that Myron simply found a version of Jet, and developed a way to mass produce it with post-war technology.
Pre-War Jet
We know for a fact thatJet existed before the Great War, since we can findreferences to it in Vault 95. In it, people addicted to plenty of drugs (Jet included) were lured in with the promise of rehabilitation, only to be used for a social experiment about drug abuse.
This means thatJet was already widely popularbefore the Great War, even when other more conventional drugs were on the market. Yet those drugs largely came from outside the U.S., so asthe country became more isolated and poor, the availability of said drugs became scarce.
If we trust Myron about how Jet is made,the entire production line of the chemicalwould be localized inside the United States. The companies that fed their cattle the failed modified protein likely sawthe same effect on their workers as Myron did: they were getting high on fumes alone.
With a stable source of the product and lack of competition,these companies are the most likely creators of Jet, finally being able to recoup the costs of their failed protein experiment.Their modified cattle would later roam the wasteland as Brahmin, but Myron wasn’t the first post-war chemist to develop the drug from their dung.
Fallout 76
Fallout 76 has no way for a player to consume the famed chemical, but that doesn’t mean it isn’t mentioned. There were already faint references in the first updates of the game, with terminals in the Wild Appalachia update mentioningpeople getting high from “cow droppings.”
The most direct mention in Fallout 76 is made by Beckett, in the year 2103. He mentions it as a largely established drug alongside Buffout and Psycho, making it as widely available and popular as it was before the bombs dropped 26 years prior.