I'll say the same thing of riding "friends" in your car. If you know someone uses cocaine or some other substance or you don't know them that well, you might consider not riding them in your car.
They may explain that they will claim ownership if you are ever stopped by police, but then you never know, do you? People can be fair weather friends.
I don't know for sure. I will tell you that I hang out with a pretty square bunch of people though, so my chances are pretty low. Call it risk management if you will.
But life is full of "taking chances." All we can do is live a good clean life and believe that justice will prevail.
Sometimes it doesn't. That is reality. I accept that as a small risk every morning when I get up. It is the cost of doing business, so to speak.