Depends on the island. Likely you will have to have it shipped in. I was (and still am) on Advair for my asthma, and I had to have it shipped to Dominica when I was there.
As far as notifying them of ADHD, the typical question you will get now (and for the rest of your career) is whether you will require a "special exception" for testing, to do your job, etc. Back in U.S., this is really only critical if you expect that you will need accommodation in order to get more time to take a test or to practice medicine.
Not notifying them up-front may have downstream legal ramifications under the
ADA if you were ever to file a claim for, say, wrongful dismissal or wrongful termination. Unless your status changes while in school or while employed, they could argue that you never notified them that you had a "disability" prior to accepting a position (etc.) if you don't tell them up front.
Any doubts, run it by a lawyer (which I am not... and this is NOT legal advice.
🙂 )
-Skip