Warning: The following contains SPOILERS for Superman and Lois season 2.
Superman and Lois revealed that X-Kryptonite can be used to temporarily give powers to humans, but it has yet to be explained why it brings about different changes in all the teenagers in Smallville who use it. The prevailing theory is that X-Kryptonite acts as a catalyst, with random effects for each based on their metagene potential. However, it is also possible that each piece of X-Kryptonite awakens a different superpower in its , in the same way that individual pieces of Red Kryptonite have unique effects on Superman and other Kryptonians.
X-Kryptonite was introduced to the Arrowverse in Superman and Lois season 1, where it was an important part of the process used to turn the citizens of Smallville into suitable hosts for the Kryptonian consciousnesses contained within the Eradicator program. The applications of X-Kryptonite were expanded in Superman and Lois season 2, with the revelation that it could be used to temporarily give Superman's powers to those who ingested it. The first of these s was a drug dealer named Phillip Karnowsky, who used an inhaled substance to fight the Man of Steel after temporarily gaining increased strength. The substance he used was later identified as Yellow Mist, a refined version of X-Kryptonite, which was also being sold to Smallville High School students by Jonathan Kent's girlfriend, Candice Pergande.
Jonathan began using Yellow Mist after learning that his rival, Timmy Ryan, had been using X-Kryptonite to boost his strength. Candice warned Jonathan that Yellow Mist had different effects on different people, with one girl reporting that she developed super-hearing, while most seemed to develop super-strength. In Jonathan's case, he conveniently developed enhanced senses that improved his throwing accuracy. Beyond setting up an anti-drug storyline, this also raised the question of just how X-Kryptonite works on a scientific level and why its effects are random.
X-Kryptonite In The Comics
X-Kryptonite first appeared in a Supergirl story in Action Comics #261 in February 1960, where Supergirl attempted to develop an antidote for Kryptonite poisoning after recovering a meteorite made of pure Kryptonite that had crashed near the orphanage she lived in. Her experiments failed, yet Supergirl somehow altered the radioactive properties of one Kryptonite fragment so that it temporarily gave Kryptonian powers to her pet cat, Streaky. Streaky regained his powers sporadically throughout the 1960s and served in the Legion of Superpets alongside Krypto the Superdog, until all of Earth's Kryptonite was turned to iron in Superman #233 in January 1971. This included the piece of X-Kryptonite that gave Streaky his powers, as confirmed by editor E. Nelson Bridwell, in answering a reader's letter in the January 1973 issue of Supergirl #2.
X-Kryptonite was later confirmed to be a naturally occurring isotope and capable of giving Kryptonian powers to humans. This was revealed in a Supergirl story in 1980's Superman Family #203, where Supergirl encountered another variant of Supergirl dressed in her old costume. This new Supergirl was revealed to be an amnesiac young woman named Ellen Leeds, who happened to witness Supergirl's arrival on Earth and lapsed into a coma after her body was overpowered by the effects of a piece of X-Kryptonite. This was the first instance of Kryptonite giving superpowers to humans in the comics, but the X-Kryptonite of the Arrowverse works differently.
Theory 1: X-Kryptonite Awakens The Metagene
In considering the question of how X-Kryptonite affects a human body, one must consider the metagene. This is the evolutionary trigger that enables people in the DC Comics multiverse to develop superpowers in moments of great stress. While it is unknown just what percentage of humans in the Arrowverse have the metagene, it has been shown that there are metahumans who developed superpowers outside the influence of mass events such as the STAR Labs particle accelerator explosion in Black Lightning. This makes it plausible that X-Kryptonite might act as a metagene trigger and that the random effects of X-Kryptonite are based upon the 's own genetics.
Unfortunately, there is one major flaw with this theory. Typically, once the metagene is triggered, it remains active unless an outside influence (like Cisco Ramon's metagene cure) deactivates it. Given that the effects of Yellow Mist are temporary and multiple doses are required to keep the effects going, it seems likely that X-Kryptonite does not affect the metagene in most humans. While it's possible it might trigger a permanent change, that doesn't seem to be the case for Jonathan Kent and Smallville's other superpowered teenagers so far.
Theory 2: Each X-Kryptonite Piece Has A Unique Effect
The other explanation for why every of Yellow Mist seems to experience the drug differently could be that different pieces of X-Kryptonite yield different superpowers. This seems to be the case with other formulas that grant temporary superpowers, such as the metahuman boosters created by Dr. Lynn Stewart in Black Lightning, which drew upon the DNA of various metahumans and only worked for an hour at a time. It's possible that the various Yellow Mist formulas work the same way.
It should be noted that there isn't a precedent for X-Kryptonite working this way in the comics and there isn't enough evidence to offer a definitive answer. Only Ellen Leeds was recorded as having been empowered by X-Kryptonite and she gained all the same powers as Supergirl rather than a single superpower. However, the randomized effects of the Arrowverse X-Kryptonite do mimic a different form of Kryptonite from the comics, which is also numbered among the forms of Kryptonite in the Arrowverse; Red Kryptonite.
First appearing in 1958's Adventure Comics #255, every individual piece of Red Kryptonite has a unique temporary effect upon those Kryptonians exposed to it. Some altered the Kryptonian's personality, with various pieces causing Superman to lose his inhibitions and Supergirl to lose her empathy. Other pieces altered their physicality, with Superman being transformed into a lion-headed beastman and a berserk giant by different pieces. Thankfully, the random effects of Red Kryptonite typically wear off after a day or two. This seems similar to how the X-Kryptonite of the Arrowverse acts on Superman and Lois.