Can you test positive for marijuana right away?

yes, you eye lids will flutter a lot of the time, It also gets in your lungs and therefore it goes into the blood also. So you can get blood tested for it, and people can see that you may be high, however, nobody except maybe police do blood tests. For it to show up in urine for a normal drug test takes a number of hours for it to metabolize and get filtered by the kidneys. So if you are clean, you could smoke right before a urine test and pass. I wouldn't recommend it though.