Substance Abuse

Chapter 3, Part C: Trends cont'd

Initiation of Substance Use

D. Initiation of Substance Use

Information on substance use initiation, also known as incidence or first-time use, is important for policymakers and researchers. Measures of initiation are often leading indicators of emerging patterns of substance use. They provide valuable information that can be used in the assessment of the effectiveness of current prevention programs and in determining where prevention efforts need to focus.

Estimates for the annual number of new users of marijuana clearly show the increases in initiation among adults and youths during the late 1960s and early 1970s, declines during the 1980s, and increases among youths during the early 1990s (Figure 5.1). However, recent methodological assessments of these long-term trend estimates based on calendar year of initiation have suggested that they are biased, due to suspected recall errors that seem to increase with the length of recall (Gfroerer et al., 2004). Evidence of telescoping, where respondents shift their reported age at first use either closer to their current age or further from the interview date, also has been found (Golub, Johnson, & Labouvie, 2000; Johnson & Schultz, in press).

Figure 5.1 Annual Numbers of New Users of Marijuana: 1965-2003

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Therefore, this report introduces a new approach for studying substance use initiation based on information on use within the past 12 months from NSDUH. Estimates discussed in this chapter describe initiation of substance use that occurred in the 12 months prior to the interview, and individuals who initiated use within the past 12 months are defined as recent initiates. Estimates for each year are produced independently based on the data from the survey conducted that year. This should improve the comparability of estimates across years, giving a more accurate assessment of recent trends. Although this approach will not eliminate reporting biases, it should minimize recall bias because the estimates are based on a more recent time period than the previously produced calendar year estimates. The more recent time period also provides more timely information on incidence. Finally, an advantage of this approach is that initiation estimates can be analyzed in conjunction with past year prevalence estimates because they reflect the same time period. For example, this approach allows the estimation of initiates as a proportion of past year users. For specific substances, initiation prior to age 12 is not well covered, and initiation prior to age 11 is not included at all. This problem primarily affects estimates of initiation for cigarettes, alcohol, and inhalants because they tend to be initiated at a younger age than other drugs.

Illicit Drugs

• In 2004, an estimated 2.8 million persons used an illicit drug for the first time within the past 12 months—approximately 7,000 per day. This was not significantly different from the number in 2002 (2.7 million) or 2003 (2.6 million). Most initiates (58.1 percent) were younger than age 18 when they first used, and the majority of new users (57.9 percent) were female. The average age at initiation was 20.1 years.
• The drug category with the largest number of recent initiates was nonmedical use of pain relievers (2.4 million), followed by marijuana (2.1 million), nonmedical use of tranquilizers (1.2 million), and cocaine (1.0 million) (Figure 5.2). Inhalants had the youngest average age at first use (16.0 years), followed by marijuana (18.0 years) (Figure 5.3).

Figure 5.2 Past Year Initiates for Illicit Drug Categories: 2004

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Figure 5.3 Mean Age for Past Year Initiates, by Illicit Drug: 2004

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Marijuana

• In 2004, an estimated 2.1 million persons had used marijuana for the first time within the past 12 months—approximately 6,000 per day. This estimate was not significantly different from the number in 2003 (2.0 million). However, there was a significant decline in the number of recent marijuana initiates between 2002 (2.2 million) and 2003 (2.0 million).
• Most (63.8 percent) of the 2.1 million recent marijuana initiates were younger than age 18 when they first used. Among youths aged 12 to 17, an estimated 5.0 percent had used marijuana for the first time within the past year, which was similar to the rate in 2003 (4.9 percent).
• Consistent with the decline in current marijuana use among male youths discussed in Chapter 2, the initiation rate (i.e., the percentage who initiated in the past year among those who had never used) for male youths declined from 6.3 percent in 2002 to 5.2 percent in 2003 and remained unchanged in 2004 (5.3 percent) (Figure 5.4). Among female youths, there was no significant change in the incidence over the 3-year period (6.7, 6.2, and 6.3 percent, respectively).

 Figure 5.4 Past Year Marijuana Initiation among Youths Aged 12 to 17 Who Had Never Used, by Gender: 2002-2004

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• In 2004, the average age of first marijuana use among recent initiates was 18.0 years. This average increased from 17.0 years in 2002 and 17.5 years in 2003. Excluding initiation occurring at age 21 or older, the mean ages of initiation were 15.9 years in 2002, 15.9 years in 2003, and 16.0 years in 2004.

Cocaine

• In 2004, an estimated 1.0 million persons had used cocaine for the first time within the past 12 months-- approximately 2,700 per day. This was not significantly different from the number in 2002 (1.0 million) or 2003 (1.0 million).
• Most (65.8 percent) of the 1.0 million recent cocaine initiates were aged 18 or older when they first used. The average age of first use among recent initiates was 20.0 years, which was similar to the average age in both 2002 and 2003 (19.8 years).

Heroin

• In 2004, an estimated 118,000 persons had used heroin for the first time within the past 12 months. The average age of first use among recent initiates was 24.4 years in 2004. There were no significant changes in the number of initiates or in the average age of first use from 2002 to 2004.

Hallucinogens

• In 2004, an estimated 934,000 persons used hallucinogens for the first time within the past 12 months. This was not significantly different from the estimate in 2003 (886,000), but it was lower than the estimate in 2002 (1.2 million).
• Although there was little change between 2003 and 2004 in the number of past year initiates of LSD or Ecstasy, there were declines between 2002 and 2003. The number of past year LSD initiates was 338,000 in 2002, 200,000 in 2003, and 235,000 in 2004. Ecstasy initiation was 1.2 million in 2002, 642,000 in 2003, and 607,000 in 2004. Most (57.7 percent) of the recent Ecstasy initiates in 2004 were aged 18 or older at the time they first used Ecstasy. The average age at initiation of Ecstasy was 19.5 years.

Inhalants

• In 2004, an estimated 857,000 persons had used inhalants for the first time within the past 12 months. The average age of first use among recent initiates was 16.0 years in 2004, and 75.0 percent of recent initiates were under age 18 when they first used. There were no significant changes in the number of inhalant initiates or the average age of first use from 2002 to 2004.

Psychotherapeutics

• This category includes nonmedical use of any prescription-type pain reliever, tranquilizer, stimulant, or sedative. Over-the-counter substances are not included. In 2004, an estimated 2.8 million persons used psychotherapeutics nonmedically for the first time within the past year. The numbers of new users of psychotherapeutics in 2004 were 2.4 million for pain relievers, 1.2 million for tranquilizers, 793,000 for stimulants, and 240,000 for sedatives. These estimates are similar to the corresponding estimates for 2002 and 2003.
• The average age of first nonmedical use of psychotherapeutics among recent initiates was 24.7 years. For specific drug classes, the average ages were 23.3 years for pain relievers, 25.2 years for tranquilizers, 24.1 years for stimulants, and 29.3 years for sedatives.
• In 2004, the number of new nonmedical users of OxyContin^® was 615,000, with an average age at first use of 24.5 years. Comparable data on past year OxyContin^® initiation are not available for prior years, but calendar year estimates of OxyContin^® initiation show a steady increase in the number of initiates from 1995, the year this drug was first available, through 2003 (Figure 5.5).

 Figure 5.5 Annual Numbers of New Nonmedical Users of OxyContin^®: 1995-2003

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• The number of recent new users of methamphetamine nonmedically was 318,000 in 2004. Between 2002 and 2004, the number of methamphetamine initiates remained level at around 300,000 per year. The average age of new users was 18.9 years in 2002, 20.4 years in 2003, and 22.1 years in 2004.

Alcohol

• In 2004, an estimated 4.4 million persons had used alcohol for the first time within the past 12 months--approximately 12,000 per day. This was significantly greater than in 2002 (3.9 million) and 2003 (4.1 million).
• Most (86.9 percent) of the 4.4 million recent alcohol initiates were younger than 21 at the time of initiation.
• In 2004, the average age of first alcohol use among recent initiates was 17.5 years. This average age was 16.7 years in 2002 and 16.5 years in 2003, but these are not statistically different from the average age of first use in 2004. Excluding initiation occurring at age 21 or older, the mean ages were 15.5 years in 2002, 15.6 years in 2003, and 15.6 years in 2004.

Tobacco

• The number of persons who smoked cigarettes for the first time within the past 12 months was 2.1 million in 2004, which was not significantly different from the estimates for 2002 (1.9 million) and 2003 (2.0 million). Most new smokers were under age 18 when they first smoked cigarettes (67.8 percent).
• In 2004, the average age of first cigarette use among recent initiates was 16.7 years. This average was similar to the averages in 2002 (16.9 years) and 2003 (16.9 years). The average age in 2004 was similar for males (16.6 years) and females (16.8 years).
• The initiation rate (i.e., the percentage of nonsmokers who initiated cigarette use within the past 12 months) was 2.6 percent in 2002, 2003, and 2004. Among youths aged 12 to 17 years, the incidence showed no significant changes during this period in that it was 6.7 percent in 2002, 6.6 percent in 2003, and 6.8 percent in 2004. This pattern was observed for both male and female youths (Figure 5.6).

Figure 5.6 Past Year Cigarette Initiation among Youths Aged 12 to 17 Who Had Never Smoked, by Gender: 2002-2004

• In 2004, the number of persons who had started smoking cigarettes daily within the past 12 months was 1.1 million, or about 3,000 per day. This estimate is similar to the estimates for 2002 (1.0 million) and 2003 (1.1 million). An estimated 49.5 percent, or 0.5 million (about 1,500 per day), of these new daily smokers were younger than age 18 when they started smoking daily.
• The average age of first daily smoking among recent new daily smokers in 2004 was 18.8 years. This was not significantly different from the average in 2002 (19.9 years) or 2003 (19.8 years), and the average age did not differ between males (19.0 years) and females (18.6 years) in 2004.
• In 2004, an estimated 3.1 million persons aged 12 or older used cigars for the first time in the past 12 months, a significant increase in the number of initiates from 2003 (2.7 million) but unchanged from 2002 (2.9 million). Although in 2004 there were approximately the same number of past year initiates of cigar use among males and females (1.6 million and 1.5 million, respectively), females initiated at an older age (22.7 years) than males (20.1 years). The overall average age at first cigar use was 21.3 years.
• The number of persons aged 12 or older initiating use of smokeless tobacco in the past year was similar in 2002 (951,000), 2003 (928,000), and 2004 (999,000). In 2004, the number of males who were first-time users of smokeless tobacco in the past 12 months was between 2 and 3 times higher than the number of females (727,000 vs. 272,000). A similar pattern was seen in both 2002 and 2003.
• The average age of first smokeless tobacco use among recent initiates in 2004 was 19.7 years. Averages were 19.1 years for males and 21.3 years for females.

(SAMHSA, 2005)