How do sedatives affect one's ability to respond quickly enough?

Impair: They impair your mental acuity . Do not drive or make legal decisions if you took sedatives. You're impaired the same way or more as you drank alcohol.

Sleepy Brain: Sedatives are essentially medications that decrease the ability of the brain to function at its normal efficient level. This does not mean that nervous impulses are not getting to the brain at their normal speed, but it does mean that our ability to process and then act on the information we are provided is affected. Because of these effects our reaction time is slowed.