L'objectif de cette thèse composée de six articles théoriques et empiriques, est d'identifier les moyens les plus efficaces d'encourager les usagers de drogues – légales et illégales – à adopter des habitudes plus saines en réduisant leur consommation. La première étape consiste à évaluer l’ampleur du problème en mesurant le coût social des drogues (tabac, alcool et drogues illicites) en France en 2010. Malgré les campagnes de prévention massives, la proportion inquiétante des consommateurs de substances nocives, mais surtout, la part élevée de personnes déclarant regretter d'avoir commencé leur consommation, conduisent à reconsidérer le paradigme traditionnel de l’addiction rationnelle, à la base de la plupart des travaux de recherche sur les addictions en économie. Au contraire, admettre une polyphasie cognitive chez les individus avec d’une part, un planner prenant ses décisions aussi rationnellement que ses capacités cognitives ne le lui permettent, et un doer ne cherchant qu’à atteindre une satisfaction immédiate, permet de construire un cadre théorique original tenant compte des émotions de court terme et de long terme des agents, ainsi que le rôle des normes sociales sur leurs décisions de consommation addictives. Le modèle construit à partir de ce cadre, ainsi que son analyse sur un panel de fumeurs français, permet de proposer des politiques novatrices visant à renforcer la motivation des individus à arrêter leur consommation addictive en réduisant leurs problèmes d’autocontrôle, en agissant sur leur perception des dangers liés à l’usage de drogues, et en ciblant un changement normatif de leur consommation. La plupart de ces recommandations ne sont pas applicables aux drogues illégales en raison de leur statut juridique. De ce fait, le seul levier permettant de définir une stratégie visant à réduire les coûts induits, est l’étude des alternatives juridiques à la pénalisation de la consommation, en particulier en ce qui concerne le cannabis, qui est la drogue illicite la plus largement utilisée en France, mais également dans la plupart des pays développés. / The objective of this thesis, composed of six academic papers, is to identify how to encourage people to adopt healthier habits by reducing their ⎯ legal and illegal ⎯ drug consumption. The first step is to evaluate the importance of the problem by measuring the social costs of drugs (tobacco, alcohol, and illegal drugs) in France in 2010. Despite massive prevention campaigns, the worrying proportion of harmful substance users and the high proportion of individuals who declare they regret having started consumption leads to reconsideration of the traditional paradigm of rational addiction and its extensions at the basis of most research works on addiction in economics. In contrast, admitting that individuals exhibit a dual process of reasoning, with a planner acting as rationally as the individual’s cognitive capabilities permit on the one hand and a doer who only seeks short-term rewards on the other, allows the construction of an original theoretical framework that takes into account consumers’ short-term and long-term emotions, and the role of social norms in addictive consumption. The model built from this framework and its testing through an analysis of smokers permit the proposal of innovative policies aiming to enhance individuals’ motivation to quit addictive consumption by (i) reducing their self-control problems, (ii) acting on their perception of the danger of the drug, and (iii) by targeting a normative change. Most of these recommendations are not applicable to illegal drugs due to their legal status. Thus, the strategy to reduce harm in this instance is to study the legal alternatives to the criminalization of use, especially for cannabis, which is the most widely used illegal drug in France, as it also is in most developed countries.

The word 'marijuana' was introduced to Australia by the US Bureau of Narcotics via the Diggers newspaper, Smith's Weekly, in 1938. Marijuana was said to be 'a new drug that maddens victims' and it was sensationally described as an 'evil sex drug'. The resulting tabloid furore saw the plant cannabis sativa banned in Australia, even though cannabis had been a well-known and widely used drug in Australia for many decades. In 1964, a massive infestation of wild cannabis was found growing along a stretch of the Hunter River between Singleton and Maitland in New South Wales. The explosion in Australian marijuana use began there. It was fuelled after 1967 by US soldiers on rest and recreation leave from Vietnam. It was the Baby-Boomer young who were turning on. Pot smoking was overwhelmingly associated with the generation born in the decade after the Second World War. As the conflict over the Vietnam War raged in Australia, it provoked intense generational conflict between the Baby-Boomers and older generations. Just as in the US, pot was adopted by Australian Baby-Boomers as their symbol; and, as in the US, the attack on pot users served as code for an attack on the young, the Left, and the alternative. In 1976, the 'War on Drugs' began in earnest in Australia with paramilitary attacks on the hippie colonies at Cedar Bay in Queensland and Tuntable Falls in New South Wales. It was a time of increasing US style prohibition characterised by 'tough-on-drugs' right-wing rhetoric, police crackdowns, numerous murders, and a marijuana drought followed quickly by a heroin plague; in short by a massive worsening of 'the drug problem'. During this decade, organised crime moved into the pot scene and the price of pot skyrocketed, reaching $450 an ounce in 1988. Thanks to the Americanisation of drugs policy, the black market made 'a killing'. In Marijuana Australiana I argue that the 'War on Drugs' developed -- not for health reasons -- but for reasons of social control; as a domestic counter-revolution against the Whitlamite, Baby-Boomer generation by older Nixonite Drug War warriors like Queensland Premier, Bjelke-Petersen. It was a misuse of drugs policy which greatly worsened drug problems, bringing with it American-style organised crime. As the subtitle suggests, Marijuana Australiana relies significantly on 'alternative' sources, and I trawl the waters of popular culture, looking for songs, posters, comics and underground magazines to produce an 'underground' history of cannabis in Australia. This 'pop' approach is balanced with a hard-edged, quantitative analysis of the size of the marijuana market, the movement of price, and the seizure figures in the section called 'History By Numbers'. As Alfred McCoy notes, we need to understand drugs as commodities. It is only through a detailed understanding of the drug trade that the deeper secrets of this underground world can be revealed. In this section, I present an economic history of the cannabis market and formulate three laws of the market.