Scalosian water
Scalosian water was water from the planet Scalos which, when imbibed, hyper-accelerated the drinker so that they moved so fast that they could not be seen by anyone who was not so accelerated. The acceleration was caused by radioactive contamination which, with long term exposure, caused sterility in males. 

Those newly accelerated were highly susceptible to  damage. A simple scratch would be fatal, resulting in apparent rapid aging.

While under hyper-acceleration, phaser beams moved slowly enough relative to the subject's perception of time that they could be easily avoided by simply stepping aside. 

In 2268, James T. Kirk was hyperaccelerated  without his consent by , who put Scalosian water in his coffee. Doctor Leonard McCoy determined this and created a counteragent, which Spock proceeded to give to the captain by drinking the water himself and delivering it once in the same state. Kirk drank the counteragent and returned to normal, while Spock remained hyperaccelerated in order to repair damages wrought on the  by the Scalosian intruders. ()
Chemical compounds