Occupational Health Screening - midwifery uni degree

I'm looking to apply for midwifery next year. Many of the courses state I'll have to complete an occupational health screening prior to the beginning of the course.

The issue I have is that I'm a daily weed smoker. I use it to help me sleep, but I don't have a medical prescription. I'd like to continue smoking as I know midwives work random hours and this will help ensure I can sleep when I need to.

Will the occupation health screening test for drugs too? I'll quit if I have to, but I'd rather not if I can avoid it.