If it's a public Uni, like a state one, they can not ask for diagnosis or anything like that for admittance. I would be cautious and say health issues. They can not press you. I have faculty family members at different schools, all state run public. When the AIDS crisis really got bad, a lot of safeguards were put in place in higher ed to prevent discrimination based on health.
Now if you need accommodation under ADA, you will have to get more specific. However that is also highly regulated. You only present a doctor or therapist info to an office that handles it. Different names on different campuses, but They are very easy to locate. Health issues covers mental health as well. I have asked for and been given accommodation at two different stats unis, everyone was very nice. They deal with mental illness related requests all the time. They won't be angry or accuse you of lying due to bipolar.
If you aren't currently using marijuana, that is info you do not want to give them. Basically don't admit to previous illegal drug use. If it has no bearing on how you will do at Uni now, they don't need to know.
As i said, I have bipolar and am a grad student. It is doable.