Velocity serums

Velocity 9 is a drug to temporarily enhance the Speed Force in a speedster's system, or even temporarily restore a former speedster's connection to it, developed by Dr. Harrison Wells. The drug is also very dangerous as it caused Jay Garrick to lose his speed and is the cause of his cancer like disease.

History
Wells first set about developing such a drug after Zoom appeared on his Earth; it was first meant to help the Flash (Jay Garrick) in his struggle against the supervillain. However, the first five attempts (Velocity 1 to 5) were failures. The sixth version of the formula was the cause of the loss of Jay's powers.

The drug was first mentioned by Wells after he had gone over to Earth One and had joined Team Flash against Zoom; he explained its story to Caitlin Snow. She was able to help him reach a successful iteration of the drug by bringing her biochemistry background into the equation; she pointed out that for the drug to work it needed to release extra oxygen, which could be achieved by adding sodium chlorate. This produced the sixth (and the first successful) iteration of Velocity.

Wells and Caitlin called Jay to the lab, because, as the former said, he was the perfect test subject as someone who had had the Speed Force in its system; Jay sternly refused to assume the drug, believing that the Speed Force could not be replicated in laboratory and that there was no telling what the Velocity-6's effect would be. However, after Wells was shot by Patty Spivot, Jay took the drug, albeit with some reluctance; it proved successful in temporarily restoring his connection to the Speed Force, enabling him to retrieve the bullet in Wells' body. Despite this, when Wells later thanked Jay for saving his life, Jay warned him to keep the drug away from Barry.

During Barry's absence from Earth-One, Central City was attacked by Geomancer and Jay Garrick had to take Velocity-7 to stop him. Caitlin made a version called Velocity-8, but skipped forward to the development of Velocity-9 after fixing the problems in the formula. Velocity-9 was the first version of the Velocity compound to not cause any bad side effects and triggered Jay Garrick's latent regenerative abilities, which fixed some of the damage to his cells that was caused by taking a failed version of the compound. Velocity-9 lasted long enough for Jay to save the people in a building and create a vortex to stabilize the breach.

While Caitlin was working on Velocity 9, she sent information on 3 of the 8 components of it to Eliza Harmon to get help on an issue with it and Eliza Harmon reverse engineered it for herself and became Trajectory. It was shown that it can also grant a non speedster super speed. Side effects such as a split personality from cellular damage and a change of speed force lightning from yellow to blue were observed in Trajectory right before she disintegrated from the cellular damage. It was also revealed that Zoom was Jay Garrick's speed clone and he was created as a result of Jay Garrick taking Velocity after Cisco touched his helmet.

Characteristics
The Velocity drug can temporarily increase a speedster's speed beyond their normal limits, however, there are several side effects of this drug. If they use it too many times, a natural possessor of the speed force will eventually lose their speed, and will cause them to slowly die due to cellular damage similar to cancer or terminal illness. If too much of the drug is taken, the speedster could start to develop an evil split personality as seen with Trajectory and Jay Garrick's speed clone Zoom due to the cellular damage affecting the brain. Taking too much Velocity could turn a speedster's lightning blue as it did right before Trajectory disintegrated and as seen with Zoom.

Caitlin Snow created Velocity 7 to help Jay Garrick temporarily get his super speed back, however his speed disappeared in the middle of his fight against Geomancer, Caitlin created Velocity 8 (off-screen) however, it had a lot of kinks, Caitlin then created Velocity 9 (off-screen) that can last longer then Velocity 7 and Velocity 8, it does not have most of the kinks that Velocity 8 has.

Known users

 * Jay Garrick/The Flash (deceased)
 * Eliza Harmon/Trajectory (deceased)
 * Zoom (Jay Garrick's split personality speed clone)

Behind the scenes

 * In the DC comics, a similar drug/serum called Velocity 9, was created by Vandal Savage with the ability to give a temporary speed enhancement and was sold in the illegal drug trade.
 * Another variation called Speed Juice exists in the mainstream comics as well. This variation is the power source of the Flash's Crime Syndicate counterpart, Johnny Quick
 * Velocity 7, 8, and 9 are the results of Caitlin Snow's attempts to restore Jay's speed. Velocity 7 wears off quickly, as proven with Jay's fight with Geomancer. Production of Velocity 8 was skipped in favor of Velocity 9, which had all of the kinks of Velocity 8 worked out. Velocity 9 had a longer duration and the added side effects of fixing Jay Garrick's cells.