GH.325 is one of a number of drugs derived from the blood of a Kree corpse code named "G.H.". When administered, the drug causes rapid healing by promoting advanced cellular regeneration, healing severe and fatal wounds, and in some cases can even revive the recently deceased.
In the closing days of World War II, the Strategic Scientific Reserve conducted a raid on one of the final active HYDRA bases, a secure research facility. After taking control of the base, the Strategic Scientific Reserve took custody of all assets and artifacts within the base, among which was the corpse of a Kree, which had been part of an attempted invasion force that visited Earth thousands of years ago and was left behind.
The corpse, given the designation "G.H.", was transferred to a facility known as the Guest House where it was studied intensively. From the G.H.'s bodily fluids, scientists were able to synthesize a number of advanced drugs with varying effects on human biology, including the serum GH.325, a serum with the potential to revive the recently deceased.
The supervisor of the project, S.H.I.E.L.D. agent Phil Coulson, authorized testing of the drug on other agents, including one diagnosed with a terminal illness. At first, the agents were closely watched and showed signs of complete recovery; however, they each eventually developed the same form of psychosis, demonstrating a persistent need to carve a series of unusual symbols of which they had no prior knowledge, and an unhealthy obsession with determining the symbols' meaning. Doctor Goodman, one of the chief medical scientists working on the project, suggested erasing the memories of all of the patients regarding the project to erase the genetic memories implanted on them by using the GH.325, and to give them new identities so they could continue living normal lives.
Having witnessed the psychological breakdown of all of the test participants and the unethical methods used to heal them, Coulson made a final report in which he appealed to S.H.I.E.L.D.'s director, Nick Fury, to have Project T.A.H.I.T.I. terminated due namely to the horrific side effects of the GH.325 serum and its related procedures, while also resigning from his position as supervisor.
Resurrections and Secrets
When Agent Coulson himself was fatally stabbed through the heart by the rogue Asgardian, Loki, S.H.I.E.L.D. Director Fury used his connections to allow Coulson to undergo a series of intensive surgeries at the Guest House that brought him back to life after being dead for several days. Among the processes used on Coulson was the administering of the GH.325 serum, which had the effect of completely regenerating his eviscerated heart tissue. However, the use of this serum, along with all other details of his resurrection, was kept secret from Coulson after his memories of the operation were erased.
Later, during a mission carried out by Agent Coulson's personal team, Skye, an inexperienced asset recruited by Coulson, was shot twice in the abdomen and left for dead. This event deeply affected Coulson, who felt personally responsible, motivating him to research all aspects of his mysterious resurrection in order to find something capable of saving Skye's life. His search led him and a small team to execute an unwilling raid on the Guest House in search of the drug. While the GH.325 was successful in restoring Skye's health, the raid resulted in the destruction of the Guest House, burying all existing stock of the drugs, along with its source, excluding a few vials, containing other GH formulas, which were retrieved by John Garrett in secret.
Upon learning of the miracle drug's true source, Agent Coulson became extremely apprehensive of its use and possible side effects on himself and Skye. At his behest, Coulson had his team member and S.H.I.E.L.D. scientist Jemma Simmons actively monitor the serum's effects on Skye. Personally interested in how the GH.325 could benefit humanity, Simmons hoped to recreate the drug by repeatedly analyzing Skye's blood. However, she was unable to discover anything unusual in the blood samples, even when comparing them to Coulson's blood. When she asked Coulson to send blood samples to their Headquarters in order to analyze them and mend her lack of available resource, Coulson denied permission without explaining to Simmons the real reason for doing so.
Agent Simmons continued to research and analyze the drug in secret, eventually gaining access to a better lab at the Hub. Unfortunately, before much progress could be made, Simmons was interrupted by the Assault on S.H.I.E.L.D. by HYDRA sleeper agents. Following the assault, Grant Ward passed on an encrypted hard drive containing all of Simmons' GH.325 research to his HYDRA superior John Garrett. 
John Garrett, in order to further Project Centipede's goal of creating its own super soldier, liberated Project Centipede's former associate Raina from prison, asking her in return to create a synthetic version of the lost GH.325 serum, using the vials of other GH serums that he had retrieved earlier. After accessing an encrypted hard drive containing all of the information gathered by Coulson's Team, and researching blood samples from Coulson and Skye, Raina was able to duplicate something she believed was similar to GH.325, though she would not guarantee its results. She ultimately used the serum on a fatally injured John Garrett after his cybernetic implants were destroyed by an EMP activated by Leo Fitz.
Under the GH.325 serum's effects John Garrett began exhibiting immediate deterioration of his mental state, declaring that he had gained some higher form of cosmic awareness or clarity of mind, but spoke in cryptic statements regarding creation and evolution while deviating from his original goals and ideals, much to Grant Ward's concern. Garrett also began carving the same complex code of symbols as the previous GH.325 subjects, carving them into a large pane of glass.
Skye, doing research into the code, learned from Ward that Garrett wrote them after his injection with GH.325. She confronted Coulson who eventually gave her full disclosure that he was writing the code and had Skye under observation to see if she was also. He revealed to her that it was theorized that he and Garrett reacted negatively to the drug because it was of extraterrestrial origin, but that she had no side effects because she might share its origins.
GH.325 is a drug known to promote rapid cellular regeneration that can be used to heal critical conditions, mortal wounds, and, in some cases, even revive the recently deceased.
In humans, the drug is known to have seriously damaging effects on the patient's psyche, with erasing or rewriting the subject's memories being the only way to alleviate the effects, but often with mixed results. The mental problems stem from the introduction of information into the subject's sub-conscious, theorized to be a result of the introduction of genetic memories from the Guest Host corpse's DNA; in most of the known cases of the drug's use, the subject gains a compulsive need to write portions of a complex code and develops an obsession with determining their meaning.
In several known cases of the drug's use, there was no detectable trace of the drug's presence in the patient's body immediately following the period of recovery, making it difficult to properly research the drug's exact effects or to replicate it. However, after months of research, Agent Jemma Simmons eventually found a way to detect if a patient was a recipient of GH.325. In any case, enough GH.325 lingered in Daisy Johnson's bloodstream after over two years for her blood to adequately substitute that of a Kree for Hive's recreation of the experiments that created Inhumans.
|Appearances for GH.325|
In chronological order:
- ↑ Agents of S.H.I.E.L.D.: 2.01: Shadows
- ↑ 2.0 2.1 2.2 Agents of S.H.I.E.L.D.: 1.14: T.A.H.I.T.I.
- ↑ 3.0 3.1 Agents of S.H.I.E.L.D.: 1.20: Nothing Personal
- ↑ 4.0 4.1 Agents of S.H.I.E.L.D.: 2.07: The Writing on the Wall
- ↑ Agents of S.H.I.E.L.D.: 1.11: The Magical Place
- ↑ 6.0 6.1 Agents of S.H.I.E.L.D.: 1.18: Providence
- ↑ 7.0 7.1 Agents of S.H.I.E.L.D.: 1.15: Yes Men
- ↑ Agents of S.H.I.E.L.D.: 1.17: Turn, Turn, Turn
- ↑ Agents of S.H.I.E.L.D.: 1.21: Ragtag
- ↑ 10.0 10.1 10.2 Agents of S.H.I.E.L.D.: 1.22: End of the Beginning
- ↑ 11.0 11.1 Agents of S.H.I.E.L.D.: 2.05: A Hen in the Wolf House
- ↑ Agents of S.H.I.E.L.D.: 3.20: Emancipation