You can. You can address verbally (by phone, for example) , you can write a statement. The police will check it. If in the course of it they establish that someone really did take drugs, then they will ask you how you found out when you noticed, do you know those persons whom they caught. If, following the results of the check, nothing of the kind is found out, then you are unlikely to be responsible for it, but each case is different.
Of course you can. You have every right to report anonymously - your right. We must react. From the last thing that I heard, we arrived within 15 minutes.
Well, first of all, it threatens you, of course, with displeasure from the gentlemen who use it. But besides you, no one will assess the risks here)