Int. J. Environ. Res. Public Health 2012, 9, 192-211; doi:10.3390/ijerph9010192 OPEN ACCESS International Journal of Environmental Research and Public Health ISSN 1660-4601 www.mdpi.com/journal/ijerph Article Do Placebo Response Rates from Cessation Trials Inform on Strength of Addictions? Robert A. Moore 1 and Henri-Jean Aubin 2,* 1 2 Nuffield Division of Anaesthetics, University of Oxford, The Churchill, Oxford OX1 2JD, UK; E-Mail: Andrew.moore@pru.ox.ac.uk Hôpital Universitaire Paul Brousse, Université Paris-Sud, INSERM U699, 12 Avenue PV Couturier, BP 200, Villejuif Cedex 94804, France * Author to whom correspondence should be addressed; E-Mail: henri-jean.aubin@pbr.aphp.fr; Tel.: +33-145-59-39-51; Fax: +33-145-59-38-63. Received: 2 December 2011; in revised form: 6 January 2012 / Accepted: 6 January 2012 / Published: 11 January 2012 Abstract: There is an implied assumption that addictions to different substances vary in strength from weak (easier to stop) to strong (harder to stop), though explicit definitions are lacking. Our hypothesis is that the strength of addictions can be measured by cessation rates found with placebo or no treatment controls, and that a weaker addiction would have a higher cessation rate than a stronger addiction. We report an overview of systematic reviews and meta-analyses of cessation trials, using randomised or quasi-randomised trials and reporting objectively-measured abstinence. The outcome for comparison was quit rates–typically the percentage of participants abstinent according to an objective test of abstinence at six months or longer. Twenty-eight cessation reviews (139,000 participants) were found. Most data came from reviews of smoking cessation in over 127,000 participants, and other reviews each covered a few thousand participants. Few reviews used data from studies shorter than three months, and almost all determined abstinence using objective measures. Cessation rates with placebo in randomised trials using objective measures of abstinence and typically over six months duration were 8% for nicotine, 18% for alcohol, 47% for cocaine, and 44% for opioids. Evidence from placebo cessation rates indicates that nicotine is more difficult to give up than alcohol, cocaine, and opioids. Tobacco is also a severe addiction, with a number of major deleterious health effects in a large number of people.