The cover letter engages the reader, but it does no contain the most important parts of a cover letter. Gender - male, female, other; sex - man, woman. In the question on age, your age intervals overlap. Why do the questions "Have you ever tried THC liquid for electronic cigarettes?" and "Is canabis usage legal in your country/city/town?" allow to select a couple of answers? In some answer options you have very informal expressions, e.g. "totally". You could've introduced a bigger variety of question types and formats. Other than that, this was a good attempt to create an Internet survey!
The survey was lacking "other option", so I had to choose an answer which is closer to my opinion, but not exactly what I'm thinking. Also in the cover letter you could have mentioned why are you doing this survey - is it for personal interest or academic research.
Good questions, but I think not a lot of people would like to answer if they had smoked marijuana or used drugs.