As of today, there isn't a known drug or drug combination that would be quick and reliable and not pose a great risk of side effects or overdose.
TASERS have a really good track record when it comes to being non-lethal. As of the last time I heard, there hadn't been a single recorded case in the US of a death due solely to the CED.
Officers have an array of options available to them today. Spray, baton, CED, and a gun.
The most effective option a police officer has, and is used 99% of the time, is his or her tactical communications.
Policing is all about communications.