2.1. Onset and Prevalence of Mental Health Disorders

Certain disorders or classes of disorders are more likely to begin during particular times in life and are thus more prevalent in certain age groups. Among adolescents between the ages of 13 and 18, lifetime anxiety disorders (e.g., generalized anxiety disorder, specific phobia) are the most prevalent (31 percent) and have the earliest median age of first onset, usually around age 6. Behavior disorders (e.g., attention-deficit/hyperactivity disorder [ADHD], conduct disorder, oppositional defiant disorder) are present in approximately 19 percent of adolescents and are most likely to first appear around age 11. Mood disorders (e.g., bipolar disorder, major depressive disorder) are experienced by approximately 14 percent of adolescents and are most likely to first appear around age 13 (Merikangas et al., 2010) (Figures 2-1 and 2-2).

Figure 2-1

Cumulative lifetime prevalence of selected mental health disorder classes among children and adolescents, by age: 2001–2004. ¹ Mood disorders include disorders such as bipolar disorder and major depressive disorder. ² Anxiety disorders include (more...)

Figure 2-2

Lifetime prevalence of selected mental health disorder classes among adolescents, by age group: 2001–2004. ¹ Mood disorders include disorders such as bipolar disorder and major depressive disorder. ² Anxiety disorders include disorders such as (more...)

Not all mental health disorders first experienced during childhood or adolescence continue into adulthood, and not all mental health disorders are first experienced before adulthood. However, adults show a similar pattern of median age of first onset and lifetime prevalence to those reported by adolescents.

Among adults, anxiety disorders (e.g., generalized anxiety disorder, specific phobia) first appear the earliest, usually around age 11, and are the most prevalent (29 percent). Mood disorders (e.g., bipolar disorder, major depressive disorder) usually appear around age 30 and are the most prevalent class of lifetime disorder among adults between the ages of 30 and 44 (25 percent). Among adults aged 18 to 44, impulse control disorders (e.g., ADHD, oppositional defiant disorder) appear relatively early, around age 11, and are more prevalent among adults aged 18 to 29 (27 percent) than among adults aged 30 to 44 (23 percent) (Figure 2-3).

Figure 2-3

Lifetime prevalence of selected mental health disorder classes among adults, by age group: 2001–2003. ¹ Mood disorders include disorders such as bipolar disorder and major depressive disorder. ² Anxiety disorders include disorders such as generalized (more...)

It is important to note that the major mental health surveys discussed above do not provide information about several types of severe but rare disorders, including schizophrenia and pervasive developmental disorders (e.g., autistic disorder). National epidemiological studies have generally not included formal assessments of these disorders, because of the challenges in accurately assessing symptoms outside of the clinic setting. Schizophrenia occurs in about 1 percent of the population and usually appears between the ages of 20 and 30 (American Psychiatric Association, 2000). Estimates of the prevalence rates of pervasive developmental disorders have varied. One recent estimate, based on data collected from 2006 to 2008, indicates that the prevalence of autism was 0.74 percent (Boyle et al., 2011).

People whose disorder begins earlier rather than later in life are more likely to experience the disorder in adulthood and have more severe symptoms. This has been found for depression, for example (Dekker, Ferdinand, van Lang, Bongers, van der Ende, & Verhulst, 2007; Pettit, Lewinsohn, Roberts, Seeley, & Monteith, 2009). As adults, people with early onset are more likely to experience suicidal symptoms, and their depression is likely to last longer (Korczak & Goldstein, 2009). A study of U.S. college students found that among students who reported symptoms consistent with a mental health diagnosis, more than half (60 percent) continued to report the same level of symptoms 2 years later (Zivin, Eisenberg, Gollust, & Golberstein, 2009).

2.2. Onset and Prevalence of Substance Use Disorders

About 11 percent of 13- to 18-year-olds have met the criteria for a lifetime alcohol or illicit drug use disorder. For adolescents, these disorders are most likely to appear around age 15. For adults, substance use disorder onset is about 20 years of age (Kessler, Berglund, et al., 2005).

Prevalence of substance use disorders increases during adolescence. Between the ages of 13 and 14, approximately 4 percent of youth meet the criteria for a substance use disorder. The rate increases to 12 percent for those aged 15 and 16 and then to 22 percent for those aged 17 and 18 (Merikangas et al., 2010).

Until adults reach the age of 60, the prevalence of substance use disorders remains relatively constant; approximately 17 percent of adults aged 18 to 29, 18 percent of adults aged 30 to 44, and 15 percent of adults aged 45 to 59 meet the criteria. However, the prevalence of substance use disorder drops to about 6 percent for adults aged 60 or older.

Research has shown that early initiation of substance use increases the risk for subsequent substance use disorder (e.g., Behrendt, Wittchen, Höfler, Lieb, & Beesdo, 2009). Figure 2-4 shows the average age of first alcohol and illicit drug use among those who initiated use in the past year. Although there is some variation across years and substances, the average age for initiating all substances was younger than 20 years.

Figure 2-4

Average age at first use among past year alcohol and illicit drug use initiates aged 12 to 49: 2007–2011. ¹ Illicit drugs include marijuana/hashish, cocaine (including crack), heroin, hallucinogens, inhalants, or prescription-type psychotherapeutics (more...)

As was true for mental health disorders, early onset of substance use disorders is associated with an increased risk of incarceration (Slade, Stuart, Salkever, Karakus, Green, & Ialongo, 2008), development of multiple substance use disorders (Bakken, Landheim, & Vaglum, 2004), and early mortality (Clark, Martin, & Cornelius, 2008).

2.3. Summary

Certain classes of disorders are more likely to begin during particular times in life. For example, anxiety disorders such as generalized anxiety or specific phobia tend to be first experienced at an earlier age than other classes of disorders. While not all mental health disorders experienced during childhood or adolescence continue into adulthood, early onset of a mental health or substance use disorder is associated with more severe symptoms and a chronic course of the disorder. Notably, many of the disorders that have been reviewed often co-occur with other disorders. The co-occurrence of disorders is prevalent and persistent across childhood, adolescence, and adulthood. Co-occurring disorders are discussed in more depth in Section 3.

2.4. References

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