If you are in a university hall of residence then you will each have your own contract with the university, things could be more complex if it is a smaller private landlord. Check to see if your contracts are linked in some way.
The difficult thing is how do you extract yourself from the problem, if it is a hall of residence you could go to the warden and complain. I am not sure if the people who you complain against would be able to work out who complained. I would suggest that you ask the warden to keep the fact that you reported that drug misuse was occuring in the flat out of the public domain, suggest that he records that a cleaner or repairperson noticed signs of drug use.
In the UK the university will be keen to act as it is a crime to allow your building to be used for the consumption of illegal drugs.
Before you do that I would suggest you go and talk to your tutor at the university or go and seek advice at the student help centre. I think it is unreasonable that you should be forced to share a flat with drug users who are smoking / snorting to get high.
Whatever you do you need to stay clean, becuase if the university think that drug use is occuring in the flat and investigate then someone in the flat might out of spite say that you were doing drugs also. If you are clean then you will be able to pass the urine test with flying colours.
_________________
Health is a state of physical, mental and social wellbeing and not merely the absence of disease or infirmity

I am not a jigsaw, I am a free man !
Diagnosed under the DSM5 rules with autism spectrum disorder, under DSM4 psychologist said would have been AS (299.80) but I suspect that I am somewhere between 299.80 and 299.00 (Autism) under DSM4.