The zombie cures were created by Ravi Chakrabarti in order to reverse zombieism and with the initial intent of curing Liv Moore, a zombie, and eventually the larger goal of preventing zombeism from becoming a major world threat.
Cure Version No. 1
Ravi initially experiments with creating a cure using Tainted Utopioum and Max Rager as components, and successfully cures a test Rat infected with the zombie virus. Despite Ravi's insistence on proceeding with caution with more testing, especially due to having enough Tainted Utopium for only 2 doses of the cure, Liv injects Blaine DeBeers, with the cure, successfully turning him back into a human to stop Blaine's practice of creating more zombie clients to blackmail. Later, Liv’s ex-fiancé, Major Lilywhite, almost dies from blood loss after being stabbed by Blaine prior. In order to save him, Liv scratched him to ensure his survival, but is angry at her for not telling about him about her being a zombie. Filled with guilt, Liv injects Major with the final dose of the initial cure to apologize.
While the cures prove effective for a time, eventually the zombie test rats revert back to being zombies, and Blaine and Major, both recipients of the cure do so as well. However even after reverting back to zombies, the cure has a side effect of eventually causing the recipients die from pneumonia, which to prevent they must take the different cure.
Cure Version No. 2
With both doses gone by Season 2, there is not enough tainted Utopium to make more of the cure, and Ravi is unable to overcome this limitation. However, Ravi convinces Blaine to help them in securing more tainted Utopium by telling him unless they take another cure, both he and Major will die. Blaine talks to Don Eberhard, believing it was him who cut the Utopium the night of the boat party. Don E. denies this, but knows of a guy called Gabriel who did cut the Utopium. Blaine, Don E. and Chief go to Gabriel and try and convince him to cut some more Utopium, in which the latter refuses due to him becoming very religious. As a result, Gabriel is tortured, and eventually turned into a zombie and starved with no brains until he agrees to make more tainted utopium. He eventually breaks, and makes more tainted utopium on the condition he receives a dose immediately as he refuses to eat brains. Ravi makes the cure but after Gabriel injects himself with it, it proves lethal, as the utopium is not the exact same formulation of the tainted Utopium from the boat party.
Later Blaine discovers Drake Holloway, a police detective found bleeding to death in Shady Plots. He and Don. E take him to the morgue where his death is inevitable until Liv scratched him. Turns out, Drake knows about the location of some tainted Utopium, he tells Liv that an old school buddy used to deal Utopium and him and another person worked for Stacey Boss and took some Boat Party Utopium, put them in condoms, then swallowed it. However they were executed and buried in a large plot, which Ravi and Major spend weeks searching with a metal detector until they find the bodies.
Unfortunately, due to the amount of time passed, most of the tainted utopium is ruined by dealers' stomach acid dissolving the condoms over time, however one of the dealer's had hid some in his anal cavity, and it provides enough tainted utopium to create 17 doses. Ravi gives Blaine and Major a dose, and despite further refinement, still tells them it's a last resort break the glass type cure. Blaine begins to suffer from coughing, so he takes the cure, which cures him and relieves him of his symptoms, but results in complete memory loss, and he is taken advantage of Don E and Chief who lie to him about them being the boss and Blaine the lackey. Don E insists that Blaine is faking, as he once heard Blaine refer to a John, an associate that an amnesiac Blaine wouldn't remember, and that by faking his amnesia he was able to turn his life around, including getting together with Peyton. Clive also claims Blaine is faking, despite no evidence, purely through his detective intuition. When Major begins to suffer from coughing, he staves off taking the cure for as long as possible with inhalers to keep the impending pneumonia at bay. Ravi tries to create treatments for memory loss, but despite Blaine's participation, none of the treatments work. With time running out, Major takes the cure when his symptoms become too serious to manage, and slowly but surely his memories start fading.
However, after hearing that Major has taken the cure and due to his amnesia has wandered off, Blaine puts it all on the line and admits to Peyton that while the memory loss was initially real, it was temporary and that it snapped back into place a few days later, and that Major will be fine. Peyton immediately cuts off contact with him, figuring that her friends could've been human months ago if Blaine had told the truth immediately. This rejection causes Blaine's "changed" personality to revert, and he steals all the remaining doses of the cure before Liv can take one.
Ravi realizes that he used a dose from his own stash on Major and that the dose he gave to Major to use on himself if his coughing fits became too serious was unused, however Major reveals that he gave the dose to Natalie after he found her, and it's later revealed she took the cure off screen.
Blaine uses the stolen doses to cure Floyd Baracus, a well known zombie and then kill him to prove the cure works, and sells the rest of the doses on the black market.
In an effort to buy time from Harley's group attacking zombies, Ravi makes up that he's working on a vaccine. Later however, he realizes the idea has merit, and creates a vaccine. He can only make a single one, as it also relies on tainted utopium, and tests it on himself. He has Liv scratch him multiple times, but he doesn't become a full time zombie, instead he has zombieism symptoms once a month, referred to as his monthlies, with all the symptoms and needs of regular zombies.
Freylich Syndrome Brains
Later in Season 4, when Liv becomes Renegade, she encounters a young girl named Isobel suffering from Freylich Syndrome who is immune from the zombie virus. It is revealed that due to the condition, people suffering from Freylich Syndrome produce a massive amount of glycoproteins in the brain, which makes them immune to the virus.
After Isobel’s death, with her blessing her brain is removed and tested on by Ravi on rats. He discovers zombie rats reverting to normal form, and persuades Liv to eat it. However, Liv after seeing that Clive, despite wanting kids, he is willing to give it up and be turned into a zombie to have a physical relationship with Dale. To spare him that fate, she gifts Isobel's brain to Dale, who reverts back to human form.
Unfortunately, Ravi neglects to mention to Isobel's mother to not mention her daughter's brain is a cure for zombieism, which unfortunately causes teens suffering from Freylich Syndrome to be targeted, as there are only a few hundred in the country. This becomes Blaine's main source of income after his businesses dry up.
With the resources of the CDC, Ravi secures enough tainted utopium so that the CDC can analyze and reproduce it, eliminating the main bottleneck in cure production. However the some of the higher ups at the CDC are more interested in developing a chronic treatment plan, instead of an inexpensive, effective, single dose cure. Liv, Ravi, and Clive, attack CDC headquarters to steal the formula, and prove the cure's effectiveness on the news. The cure is manufactured directly with available raw materials, rather than at this point, nearly non existent tainted utopium, but seems to be otherwise identical to Ravi's second version of the cure.
With an inexpensive and readily available cure, zombieism is no longer a major world threat. However, this doesn't mean zombieism becomes extinct, as many people prefer the advantages of being a zombie, such as agelessness, and nigh invulnerability, especially from diseases. Many people who became a zombie because they were suffering from otherwise life threatening ailments have no choice but to stay as zombies, but brain donations increase following more sympathy for zombies.
Liv and Major go into hiding from the public eye, and due to personal reasons decide not to take the cure, living as immortal zombies instead. Years later, they haven't aged a day while the rest of the gang are noticeably middle aged. Liv and Major convinces the others to join them in becoming zombies again, and it's implied they accept.