Thanks for your question. Have you tried using Summon? It's an all-in-one search from the library's home page: http://herrick.alfred.edu. I tried searching on Summon with the following search terms: marijuana medical new york city and got over 3,000 possibilities. Most of them were newspaper articles, but there were over 60 journal articles and several books. I think the problem may be putting legalisation and medical purposes in the same search, it eliminates articles that may be useful unnecessarily.
Please try the Summon search and see if that helps.