Cannabis sativa is the scientific name for the widely used drug commonly known as marijuana. Marijuana is the most commonly used illegal drug in the United States as well as in many other countries. Considered a "soft" drug, it is a naturally growing plant that is harvested as its crude product for use. Other familiar names for marijuana are weed, dope, pot, hemp, cannabis, and reefer. Marijuana contains tetrahydrocannabinol (THC), which is a mind altering substance that is generally smoked, but also can be taken orally or as oil on the skin in order to receive a "high." New laws regarding the marijuana's legalisation have led to more questions and increased interest in the effect marijuana has on its users. Chapter One of this book discusses differences across motivation variables and marijuana use. Chapter Two compares the medical necessity of marijuana to the political agenda. Chapter Three examines the evidence for and against the medical use of marijuana, and the effects and implications of its recent legalisation in several states especially with regard to its use by college-age young adults. Chapter Four examines the issues surrounding legalisation and teen use and the policy steps that might be taken to effectively communicate the risks to adolescents amidst an ever more socially acceptable climate. Chapter Five discusses the recent rise of legally sold marijuana, the risks of use, arguments in support of mandating warnings on packages of legally sold marijuana, the likely benefits and costs of mandating warnings, ways of evaluating proposed and actual warnings, and specific recommended warnings. Chapter Six exhibit how and the extent to which federal government marijuana regulation and policy contributes to disparities in arrest, in particular for African Americans of lower socioeconomic standing. This book ends with a commentary on aims to answer the question of whether marijuana and video games can engender "real" addictions in a way that bridges the gap between scientific and colloquial understandings of problem use.