mood disorder may be particularly vulnerable to such adverse effects resulting from marijuana doses well tolerated by others.

Cannabis-induced intoxication clearly impairs cognitive and psychomotor performance, with complex, demanding tasks being more affected and in a dose-dependent manner. The spectrum of behavioral effects is similar to those of other central nervous system (CNS) depressant drugs such as alcohol and are additive to effects produced by concurrently used depressant drugs. The magnitude of marijuana-produced perceptual and psychomotor alterations measurable in research settings is such that it is reasonable to assume that complex tasks such as driving or other tasks that have high demands on attention and information processing and reaction responses would be impaired. Of particular relevance when considering consequences of adolescent marijuana use is that in a laboratory setting, overlearned or well-practiced tasks are relatively less affected by marijuana. Thus, a beginning or relatively inexperienced driver may be more subject to marijuana-induced cognitive, motor, and perceptual impairments than an adult who has been driving for many years.

Although the evidence for cognitive impairment for some hours after a dose of marijuana is quite consistent and has been repeated in experiments in many laboratories over many years, there is less unanimity about the consequences of long-term chronic cannabis use. The consensus of recent studies is that individuals who have used cannabis over long periods of time have impaired performance on tests even when not acutely intoxicated. The cognitive functions that are impaired are attention, memory, and processing of complex information, and appear to last months, perhaps years, after cessation of use. Uncertainty remains as to whether some of the individuals had impaired performance before becoming involved with cannabis, but the data are quite consistent that the performance of heavy, frequent users is impaired when compared with shorter-term, less infrequent marijuana users.

Tolerance to many of cannabis's subjective and behavioral effects develops rapidly with relatively few exposures, not unlike the pattern of tolerance that develops to nicotine and cocaine effects when smoked. For many users, tolerance likely leads to more frequent or high-dose use to achieve the sought-after psychological effects. A cannabis withdrawal state has been clearly demonstrated in laboratory animals given marijuana or other cannabinoids over a relatively short period of time. Clinically significant cannabis withdrawal symptoms have been well described in both human laboratory studies and clinical settings. With abrupt discontinuation after only a few days of repeated administration of THC or marijuana in a laboratory setting, disturbed sleep, decreased appetite, restlessness, irritability, sweating, chills, nausea, and markedly disturbed sleep rapidly develop within hours of the last dose. Although most symptoms disappear in a day or two, irritability and sleep disturbance can persist for weeks. Frequent marijuana users in a clinical setting report similar symptoms when they stop marijuana smoking, along with a craving for marijuana, depressed mood, increased anger, wild dreams, and headaches. The pattern of withdrawal symptoms suggests to some investigators that it may contribute to continued use of marijuana in cannabis-dependent individuals. As with other addicting drugs, the precise links between withdrawal symptoms and continued or relapse to drug use is still a matter of some uncertainty.

As with nicotine dependence, it appears that early exposure to cannabinoids during adolescence may have more adverse consequences, including patterns of drug taking consistent with addiction. Individuals who began regular use of cannabis in adolescence appear to be at greater risk, relative to cannabis users who began regular use at an older age, in terms of greater use of other illicit drugs, depression, suicidal ideation and suicide attempts, and violent or property crimes. When adolescents were followed over time into adulthood, weekly cannabis use when an adolescent predicted an increased risk of dependence when a young adult.

The sometimes marked cardiovascular and autonomic system effects of cannabis appear to be well tolerated by adolescent users. However, when used heavily and over time, smoking marijuana is associated with pulmonary symptoms and problems. Pulmonary toxins are present in marijuana smoke as they are in tobacco smoke.

Recent estimates that in the future as many as 30,000 deaths a year may result in Britain from smoking cannabis reflect reasonable extrapolations from the toxic effects of marijuana to what is known about the adverse effects of tobacco smoking. Laboratory models of cannabinoid-induced alterations in immune system response are such that questions remain about the likelihood of clinically relevant immune system impairments from prolonged marijuana exposure.

In this section we provide an overview of the phenomenology of alcohol drinking and alcohol use disorders (AUDs) in adolescents ages 11 to 19 years of age. Included in this overview is a current description of “drinking youths”; prevalence rates of adolescent drinking, binge drinking, AUDs, and drinking-related consequences; pertinent diagnostic issues; and potential etiological factors that may enhance our understanding of alcohol use and the development of problem drinking in adolescents.

Alcohol is a sedative and it is the only drug in this category to be discussed in this chapter. Other sedatives such as benzodiazepines, barbiturates, and other sleeping pills are used so uncommonly that they do not merit a full discussion. Notably, a discussion of alcohol leads to some overlap in content with discussions of other substance use disorders in adolescents, discussed elsewhere in this chapter. However, there are some important distinctions to bear in mind. Alcohol use by persons 21 years or older is legal in the United States, making it more readily available to adolescents and exposing them to seductive advertisements. In addition, low to moderate alcohol use is an integral part of our adult community life. It is available in many restaurants, sold in grocery stores in many states, and is available in liquor stores throughout the country. It is readily accepted in social settings, frequently accompanying a meal, and incorporated in many religious ceremonies. Over the past decade, the health benefits of one or two glasses of wine per day have been widely covered by the media. Finally, parents and other authorities frequently overlook adolescent drinking, relegating it to experimentation or “rites of passage.” In contrast, the illegality of many of the other abused substances (e.g., marijuana, cocaine, heroin) makes them taboo in most adult circles and causes much alarm and concern in adult communities when adolescent use of illegal substances is uncovered.