Velocity is a series of drugs that allows temporary access to the Speed Force. Initially developed by Hunter Zolomon and then by Dr. Harrison "Harry" Wells as Velocity 6, the current version of the drug (Velocity 9) was created by Dr. Caitlin Snow. Despite its benefits, this drug is also very dangerous, as it causes cellular degeneration and eventually death. In addition, subjects of the serum have demonstrated mental instability or disorder, such as the split personality Eliza Harmon developed.