The water signs and Neptune are usually the most associated with drug taking and addiction. Either to seek comfort from their emotions or escape from the responsibilities and realities of life. Having said that I'm water + Neptune heavy and I've never tried any drugs and I absolutely never drink alcohol. My addiction to the internet on the other hand.......

I will say though that I would like to try Ayahuasca at some point (in a safe, reputable environment that I've thoroughly researched) and that's the other side of drugs- the spiritual element. Also I agree that the fire signs are probably the most experimental when it comes to this type of thing.