1. National Institute for Health and Clinical Excellence Chronic obstructive pulmonary disease: Management of chronic obstructive pulmonary disease in adults in primary and secondary care (partial update), NICE guidelines [CG101]. https://www.nice.org.uk/guidance/cg101 (accessed 9 Dec 2014).
2. United Nations Office on Drugs and Crime World Drug Report 2010, http://www.unodc.org/unodc/data-and-analysis/WDR-2010.html (accessed 25 Nov 2014).
3. Continued cannabis use and risk of incidence and persistence of psychotic symptoms: 10 year follow-up cohort study
4. Respiratory symptoms and lung function in habitual heavy smokers of marijuana alone, smokers of marijuana and tobacco, smokers of tobacco alone, and nonsmokers;Tashkin;Am Rev Respir Dis,1987
5. Respiratory effects of non-tobacco cigarettes.