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INTRODUCTION

This chapter aims to provide a broad overview of marijuana use and related disorders. The chapter begins with two sections, one providing historical background information and the other, current context in terms of public attitudes and laws. The next section reviews evidence for additional adverse health effects associated with marijuana use, including physical, mental, and psychosocial outcomes,1 while considering the strength of research findings to date. The following section provides information on recent trends in perceptions of harmfulness, cannabis potency, trends in adolescent use and the relationship of this to changing marijuana laws, and corresponding information about adult use and specific subgroups. Finally, clinical implications are presented in the context of current epidemiologic evidence and trends over time in an evolving legal and social landscape.

The chapter focuses primarily on information about marijuana use in the United States. Clearly, marijuana is widely used around the world,2,3 and is associated with risk for many adverse health and social consequences.3 However, cross-national prevalence comparisons, policy analyses and other projects such as estimating the global burden of disease due to cannabis are considerably hampered by cross-national differences in many factors,4 including methodological differences in survey methods that can have a substantial impact on prevalence estimates, different meaning of chronological age in terms of life course (e.g., adolescence),5 and many other cultural differences. Further, the preponderance of high-quality evidence about cannabis and its consequences comes from a limited number of high-income countries,5 particularly the United States. Therefore, this chapter focuses primarily on information about marijuana use and its consequences in the United States. The research studies reviewed here can be taken as examples that would be very useful to replicate or expand in other countries.

HISTORICAL PERSPECTIVE

Marijuana has had a long and controversial history in the United States, with marked fluctuations in public attitudes toward the acceptability and potential harms associated with its use.6 The hemp plant, from which cannabis is produced, was brought to North America as a fiber crop (e.g., for rope) by Jamestown settlers in the early 1600s, and hemp products were part of the colonial economy. An early notation of medical use appeared in 1850, when Extractum Cannabis (extract of hemp) was listed in the United States Pharmacopoeia as a treatment for numerous disorders, including neuralgia, tetanus, typhus, cholera, rabies, dysentery, alcoholism, opiate addiction, anthrax, leprosy, incontinence, gout, convulsive disorders, tonsillitis, insanity, excessive menstrual bleeding, and uterine bleeding.7 A subsequent record of marijuana as a treatment is found in the Pure Food and Drug Act of 1906, which required that any product containing “cannabis indica” be labeled as such.8 While marijuana had largely been imported to the United States from India prior to the 1900s, the U.S. Department of Agriculture Bureau of Plant Industry announced it had succeeded in growing domestic cannabis of equal quality in 1913.

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