Around people smoking marijuana-could this fail my medical examination?

Your blood test for immigration does not include tests for THC or any other drug as far as I know, but if you were being tested for this substance, it could show up in your blood stream and urine test if you did inhale second hand marijuana smoke.

I guess

Second-hand thc is not very strong or potent, but depending on the density and frequency of your exposure, you may be at risk for a failure. The odds are good if you were in a room where other people were smoking that you will be ok but the chance is always there. It depends on lots of things: was there ventilation in the room, were you directly inhaling the second hand smoke, how long is there between your last exposure and your exam, etc. Its not likely to show up in your hair, but a urinalysis may pop it up. Also, not all urinalysis tests are equal. They have different degrees of what they consider a "positive result". Some are looking for 10 micrograms per mil. of urine, some draw the line at 50 micrograms, meaning one test would show it and another wouldn't if your particular level was in between. Personally, I didn't know you would need a drug screen to get into Canada. There are several places in Canada where Marijuana is de-criminalized, meaning it's not against the law to posses or smoke it. Based on guessing your circumstances, I would say you will probably be alright, but if you're really nervous about it there are many fine detox products out there or barring that, you could always drink a lot of water before you go and pee out fresh H2O for the doc. Good Luck