Incidence and Prevalence

Illicit drugs of abuse include marijuana and hashish, heroin, cocaine (including crack), methamphetamine and its analogues, so-called club drugs, hallucinogens, and dissociative drugs (Table 30-1). Legally prescribed opioids and sedative/hypnotics are abused when used nonmedically. Alcohol is legal but is abused when consumed inappropriately or in excessive amounts. According to the 2009 National Survey on Drug Use and Health (NSDUH),⁵ an estimated 21.8 million Americans 12 years of age and older were current illicit drug users, which is higher than in 2008. This number represents approximately 8.7% of the population. Illicit drug use is highest among young persons 18 to 25 years of age. In a dental practice of 2000 patients, it can be expected that approximately 175 of them abuse at least one type of drug or other substance.

Marijuana is the most commonly used illicit drug. In 2009, there were 16.7 million past-month users. Among persons aged 12 or older, the rate of past-month marijuana use and the number of users in 2009 (6.6%, or 16.7 million) were higher than in 2008 (6.1%, or 15.2 million) and in 2007 (5.8%, or 14.4 million). In 2009, there were 1.6 million current cocaine users aged 12 or older, comprising 0.7% of the population. These estimates were similar to the number and rate in 2008 (1.9 million, or 0.7%) but were lower than the estimates in 2006 (2.4 million, or 1.0%). An estimated 3.7 million people have reported previous use of heroin, with an estimated 150,000 persons becoming new users every year.² The level of heroin use is relatively stable, with an approximate 1.5% annual increase. Methamphetamine is a synthetic drug that is easily manufactured, and its use is spreading across the United States at alarming rates. The number of past-month methamphetamine users decreased between 2006 and 2008 but then increased in 2009. The reported figures were 731,000 (0.3%) in 2006, 529,000 (0.2%) in 2007, 314,000 (0.1%) in 2008, and 502,000 (0.2%) in 2009.

The use of prescription opioids (e.g., OxyContin) for nonmedical reasons is currently one of the fastest-growing dimensions of drug abuse in the United States, with a 225% increase from 1992 to 2000.² The lifetime nonmedical use of OxyContin increased from 1.9 million to 3.1 million in the 2-year period from 2002 to 2004.⁶ From 2002 to 2009, there was an increase among young adults 18 to 25 years of age in the rate of current nonmedical use of prescription-type drugs (from 5.5% to 6.3%), driven primarily by an increase in pain reliever misuse (from 4.1% to 4.8%). The nonmedical use of opioids has become epidemic in certain parts of the nation, especially in regions on the east coast.

According to the 2009 NSDUH,⁵ slightly more than half (51.9%) of Americans aged 12 or older reported being current drinkers of alcohol. This translates to an estimated 130.6 million people, which is similar to the 2008 estimate of 129.0 million people (51.6%). In 2009, nearly one quarter (23.7%) of persons aged 12 or older participated in binge drinking. This translates to about 59.6 million people. The rate in 2009 is similar to the estimate in 2008. Binge drinking is defined as consumption of five or more drinks on the same occasion on at least 1 day in the 30 days prior to the survey. In 2009, heavy drinking was reported by 6.8 percent of the population aged 12 or older, or 17.1 million people. This rate was similar to the rate of heavy drinking in 2008. Heavy drinking is defined as binge drinking on at least 5 days in the past 30 days. The highest rates of alcohol use, heavy or binge use, and alcohol use disorders occur between the ages of 18 and 29 years.⁵

The prevalence of problem drinking in general outpatient and inpatient medical settings has been estimated to be between 15% and 40%.⁴ The lifetime prevalence of an alcohol use disorder in the United States is about 18.6% (13.2% for abuse and 5.4% for dependence).⁷ Surveys assessing past-year prevalence of these disorders indicate that nearly 8.5% (18 million) of American adults meet standard diagnostic criteria for one of the DSM-IV alcohol use disorders. Of these, 4.7% (10 million) meet criteria for alcohol abuse, and 3.8% (8 million), for dependence. Gender-specific rates of abuse and dependence differ within the general population, with men exhibiting higher rates of both abuse and dependence (8.5%) than those reported for women (4%).⁸ Although problem drinking is seen primarily in adults, the prevalence among teenagers is alarmingly high. Alcoholism among elderly persons also is a significant problem. A dental practice comprising 2000 adult patients could include as many as 170 patients who have a problem with alcohol.

Etiology

The neurobiology of addiction and dependence is complex and involves a unique set of variables. Disruption of the endogenous reward systems in the brain is a common feature of all of the major drugs of abuse; most of these drugs act by disrupting dopamine circuits in the brain.⁶ Acute changes increase synaptic dopamine and disrupt circuits that mediate motivation and drive, conditioned learning, and inhibitory controls. This enhancement of synaptic dopamine is particularly rewarding for persons with abnormally low density of the D₂ dopamine receptor (D₂DR).⁶ A complex neural circuitry underlies the valuation and pursuit of rewards³ (Figure 30-1). Although dopamine is the primary neurotransmitter involved in drug abuse and addiction, many other neurotransmitters are involved, depending on the drug of abuse (Figure 30-2). Evidence suggests that inherited genetic factors are involved in alcoholism. Psychological factors such as depression, self-medication (to relieve psychic distress), personality disorder, and poor coping skills appear to be involved in addictive behavior. Social factors that may be involved include interpersonal, cultural, and societal influences.¹

FIGURE 30-1 Brain reward circuits.

The major dopaminergic projections to the forebrain that underlie brain reward are shown superimposed on a diagram of the human brain: projection from the ventral tegmental area to the nucleus accumbens, and prefrontal cerebral cortex. Also shown are projections from the substantia nigra to the dorsal striatum, which play a role in habit formation and in well-rehearsed motor behavior, such as drug seeking and drug administration.

(From Hyman SE: Biology of addiction. In Goldman L, Ausiello D, editors: Cecil medicine, ed 23, Philadelphia, 2008, Saunders.)

FIGURE 30-2 Converging acute actions of drugs of abuse on the ventral tegmental area and nucleus accumbens. DA, Dopamine; GABA, γ-aminobutyric acid; LDT, Laterodorsal tegmentum; NAc, Nucleus accumbens; PCP, Phencyclidine; PPT, Pedunculopontine tegmentum; VTA, Ventral tegmental area.

(From Renner JA, Ward EN: Drug addiction. In Stern TA, et al, editors: Massachusetts General Hospital comprehensive clinical psychiatry, Philadelphia, 2008, Mosby.)

Marijuana

Marijuana is the common name for cannabis, which is the most commonly used illicit drug in the world.² Delta-9-tetrahydrocannabinol (THC) is the major psychoactive ingredient in substances that causes cannabis dependence. Several different preparations of marijuana are available. These preparations—bhang, charas, ganja, and hashish—are known to vary in potency and quality. They usually are smoked but can be taken orally and are sometimes mixed with food. With inhalation, peak effects occur within 20 to 30 minutes; with oral ingestion, peak effects occur within 2 to 3 hours.² Currently available marijuana supplies are much more potent than those that were available in the 1960s. Most users describe an altered sense of time and distance perception. Acute intoxication may result in anxiety and paranoid ideation or frank delusions. Tolerance and physical dependence can occur, but clinical presentation of these symptoms is not common.² Marijuana use can destabilize patients whose schizophrenia is in remission. Social and occupational impairment occurs but is less severe than that seen with alcohol and cocaine use.¹ Marijuana use rarely requires medical treatment. Anxiety reactions may require treatment with benzodiazepines. Of note, some states allow the use of marijuana for medicinal purposes.

Opioids

The primary effects of the opioids (opiate-like drugs) are to decrease pain perception, cause modest levels of sedation, and produce euphoria. Drugs in this category include those derived from naturally occurring alkaloids morphine and codeine. Semisynthetic drugs produced from morphine or thebaine molecules include hydrocodone, hydromorphone, heroin, and oxycodone. Synthetic opioids include meperidine, propoxyphene, diphenoxylate, fentanyl, buprenorphine, methadone, and pentazocine. Tolerance to any single opioid is likely to generalize to other drugs in the group.

Through direct effects on the central nervous system (CNS), opiates may produce nausea and vomiting, decreased pain perception, euphoria, and sedation. Additives in street drugs can cause permanent damage to the nervous system, including peripheral neuropathy and CNS dysfunction. Users of such drugs may experience constipation and anorexia. Respiratory depression occurs as the result of a decreased response of the brain stem to carbon dioxide tension. This effect is part of the toxic reaction to opiates,as described later on, but it also can be significant in patients with compromised lung function.

Complications are common among abusers of narcotics, especially when administered intravenously. Cardiovascular effects of the opiates are mild, and no direct effect on heart rhythm or myocardial contractility has been noted with their use. Orthostatic hypotension, probably caused by dilation of peripheral vessels, may occur. The major complication with intravenous use of these drugs involves the use of contaminated or shared needles; pathogens introduced in this manner can cause hepatitis B and C and bacterial endocarditis, and an association with increased risk for infection with human immunodeficiency virus (HIV) also has been noted.^2,6 The bacterial endocarditis is unusual in that it predominantly affects the right side of the heart (the location of the tricuspid valve), with Staphlococcus aureus being the most common causative organism.

Dependence on opiates can be seen in at least three groups of patients. The first group is the minority of patients with chronic pain syndromes who misuse their prescribed drugs. The second group at high risk consists of physicians, dentists, nurses, and pharmacists. These persons have easy access to drugs with abuse potential.⁹ Members of the third and largest group buy their drugs on the street to get high. Once persistent opiate use has been established, the outcome is often very serious. According to statistics from the Centers for Disease Control and Prevention (CDC), in 2007 pain killers killed twice as many people as cocaine and five times as many as heroin.¹⁰ From 1999 to 2007, the number of U.S. poisoning deaths involving any opioid analgesic (e.g., oxycodone, methadone, hydrocodone) more than tripled, from 4041 to 14,459.

Toxic reactions (overdose) are seen with all opiates. These reactions are more frequent and dangerous with more potent drugs such as fentanyl, which is 80 to 100 times more powerful than morphine. Intravenous overdose can lead immediately to slow, shallow respirations, bradycardia, a drop in body temperature, and lack of responsiveness to external stimulation. Emergency treatment includes support of vital signs with the use of a respirator and administration of a reversal agent such as naloxone by intramuscular or intravenous injection.²

In contrast with sedative withdrawal, withdrawal from opiates is an unpleasant but not life-threatening experience. Gastrointestinal upset, muscle cramps, rhinorrhea, and irritability are the prominent signs and symptoms. Opiate users with memory impairment or cognitive dysfunction should be assessed for HIV infection by evaluation of risk />