Many people have used or abused a substance of some kind, at some point in their life. Be it alcohol, nicotine, or illegal drugs. You need to find out about each others history and opinions with regards to each.
There can be hugely varying opinions regarding the use of different substances and it will cause a conflict if you are too far from each other. For example one of you might think smoking cannabis is okay whereas the other will completely detest it. One of you might drink far too much for the other to be comfortable with.
Also, the use or abuse of drugs can bring serious health and financial issues in the future. Are you willing to face them with your potential partner if it so happens?
Be sure to discuss all this honestly.
