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Ghouls are a staple of theFalloutfranchise, appearing in every single game and work derived from it. They used to be humans, but due to radiation exposure, they became something new, capable of surviving for centuries, but with a decaying skin and mental state.
In the Fallout show, one of the main characters is the Ghoul, who’s been around since before the Great War and is able to keep his sanity. The way he does this is by inhaling (or drinking) a strange yellow liquid out of some vials, but that begs the question, what is in those vials?

Spoilers for the Fallout show!
Ghoulification And Feral Ghouls
Ghoulification is the process in which a human, due to extreme or gradual exposure to radiation,becomes a ghoul. This new form has burnt-like skin, usually losing the nose and ears, butcan survive for hundreds of years, is immune to radiation, and can even regenerate most physical damage.
It isn’t known if ghouls can die of old age.

While there are several subtypes of ghouls, the main ones are the regular ghouls (with intellect equal to humans) and feral ghouls.When a ghoul goes feral, it acts like a rabid animal, trying to eat anything that stands in its way;once a ghoul goes feral, there is no going back.
There has never been a proper explanation as to why a ghoul goes feral, since for every feral example there is an exception. It is often agreed that,in time, all ghouls go feral, but how long it takes for each ghoul seems to be dependent on their state of mind, their surroundings, and chance.

The Vials Of The Fallout Show
When we meetthe Ghoul (his real name being Cooper Howard)in the Fallout Show, he’s trapped in a coffin with tubes connected to his body, administering a strange yellow liquid. It is suggested thatthis is how he’s avoided going feral for so long, considering he’s been around since before the Great War.
Cooper needs to constantly consume this liquid, either by drinking or inhaling it,otherwise he’ll go feral in a matter of days. While we are shown people that sell and make that product,we are never told the name of the chemicalor where it originally comes from.

With so little information, we need to look everywhere for hints of what really is inside the vials, with only two things of note from the show:
References In The Games
The device both Cooper and Thaddeus used to inhale the chemicalis similar in design to Jet, a common drug found in the Fallout games. Yetthe effects are completely different, and the color of the liquid is red in the games, instead of the yellow seen in the show.
The same model as Jet is used for Addictol, a chemical that removes any addictive or withdrawal effects someone might have from drug abuse. Yet it still lacks any similarities with the vials seen in the show, beyond being taken with an inhaler.

John Hancock And The Experimental Drug
In Fallout 4, there is one characterthat undergoes ghoulification similarly to Thaddeus. This isJohn Hancock, who, during his search for stronger drugs,ends up taking an experimental radioactive drug, which gives him an unparalleled high butturns him into a ghoulin the process.
John claims thatthe drug he took was the only one of its kind, but there isn’t a way for him to know that for certain. It is possible thatthe chemical seen in the show is the same one John Hancock encounteredin his search for exotic drugs.
Possible Origins Of The Vials
If you only know Fallout from the show, you might assume thatthe drug Cooper takes was created bythe Enclave.They are, after all, the ones with an active scientific community, with plenty of resources to develop any kind of technology they might need.
While we can’t deny the possibility,the Enclave as depicted in the games is strictly anti-mutants, making them an unlikely source. They often look for ways to eradicate mutants from the wasteland, either by force or with targeted bioweapons.
Another big player in scientific research is the Institute, mostly known for their synthetic human research, aiming to replace key figures with synthetic counterparts to take over the wasteland. They have plenty of resources to experiment and create a drug capable of turning a human into a ghoul.
The only problem with that is thatthe faction likely perished during the events of Fallout 4.This is because the Brotherhood of Steel has the Prydwen at their disposal, something they can only keep at the end of Fallout 4 if the Institute is destroyed.
Granted,they could both be the original creators of the vials and be a defunct faction, but that’s unlikely to happen. Since the show still has a lot to show us about Cooper Howard’s past, it is unlikely that we’ll see him interact with a faction that no longer impacts the world of Fallout as a whole.
Vault-Tec
In the end,the most likely answer will come fromone of the Vaults, or even Vault-Tec themselves.They conduct all kinds of experiments on their subjects, and we even haveexamples of pre-war ghoulsmade to influence a world ravaged by nuclear war.
These ghouls, like Desmond Lockheart or Eddie Winter, don’t seem to fear the possibility of them going feral.Desmond, in particular, has been active in the wasteland for a long time, and his strand of ghoulification allows him to keep both his hair and facial hair.
While we will need to wait for the show to give us definitive answers,the experiments that created the vials could have possibly made Desmondwho he is today. He’s been around for the same amount of time as Cooper, buthe needs no sustenance to avoid becoming a feral ghoul.