How long after smoking marijuana can you go for a drive and not get done for drug driving?

At least in Illinois, if there is any cannabis present in a person's blood breath or urine, then it is illegal to drive a motor vehicle. A person will test positive for marijuana for around 30 days after smoking. One does not have to be high, only have cannabis in the system. So, it is actually a month after smoking that it becomes legal to drive again.

The kid above me isn't exactly correct, the THC from marijuana stays in your system for about a month (depending on how much you smoked) but that's the blood... not urine or saliva. For saliva, to be on the safe side it takes about 12 hours after smoking to test negative. For urine, it takes about 3 days. This all depends on how much you smoked though, and other things like if you drink a lot of water. Drinking a lot of water makes you have to pee and peeing flushes your system of acids and such so drinking a lot of water would help both urine and saliva because it'll dilute the presence of THC in your saliva. So the hardest test to pass is the blood test but rest assured that you probably won't get that test since it's expensive and messy, those test probably are only given in strict places like the if your working for the FBI or something and if that's the case than you should sober up a little before you apply. The one most people worry about is the saliva test because it can be administered whenever (like after being pulled over), and you don't have the comfort of going to a bathroom and using someone elses sample. The main two places you are tested are after being pulled over and in the workplace so if you can avoid it don't smoke and drive, or if you do just make sure you stop at stop signs, drive the limit, use your turn signal, etc. In the workplace they don't test much and probably won't surprise you with a test, unless they have a reason to believe you've been doing drugs so don't come to work high. Also, there are laws in states regarding testing that you should check out, many states limit the amount of testing that can be done or ban a method. You should also ask people you can trust in the workplace (that have been there longer than you) about drug testing.