By Suzi Gage, a final year Epidemiology PhD student from the University of Bristol, looking at the relationship between drug use and mental health. She was the 2012 UK science blog prize winner and her blog, Sifting the Evidence, is part of the Guardian's science blog network. She has also just completed a Media Fellowship with the BBC. This post is part of a series of posts for the Public Attitudes to Science 2014 study.