The American Red Cross has this on their website:
Q: I’m a heavy cannabis user. Can a transfusion recipient fail a drug test if they receive my blood?
A: No.
They don’t care if you’re high as a kite as long as it doesn’t impair your memory or comprehension (probably for legal reasons).
About a decade ago, I was renting a room from a couple I was friends with. One of them went to a hairstylist and during the appointment said to her “I don’t have any girl-friends, do you want to hang out some time?”. Well that hairstylist said yes and they made plans to go snow tubing a few weeks later. I was supposed to go with them but came down with a cold. I still wanted to meet this new girl so I came down to see them off. That’s when I met the woman that would eventually become my wife and the mother of my child!
I had never been more upset that I was sick than that day lol