CO and WA Legalize Recreational Marijuana

I'm sure my friend who drives around all day on pain killers and perks would love a chat.

Correct me if I'm wrong, but, isn't it illegal to drive if you have over a certain amount of percocet in your system? I DO know for a fact that it dulls your senses tremendously, and even if it is not illegal, you still should definitely not be doing it if you take more than 1 a day; my grandmother is up to 4 every 4 hours, and we had to take her car away because it's just flat not safe for her, but even with only a couple in you per day it still slows you down a ton.