Is it legal for my university to drug test me?

I am a student at the University of Colorado, Boulder. I called for medical istance and told the medical personal that I had consumed copious amounts of alcohol and taken some adderall earlier in the day. I believed I was protected under my university's Good Samaritan policy, which turned out not to be the case. Later, I was igned sanctions, including random drug and alcohol three times a month for three months. Is this legal for my university to ask me to consent to drug tests (even when I am out of the Boulder vicinity)?