Youth Substance  Use: State Estimates From the 1999 National Household Survey on Drug Abuse

6. SEQUENCE OF SUBSTANCE USE INITIATION

A common question is, "What role does the early initiation of cigarettes and alcohol play, if any, in the first use of marijuana?" This question was addressed by analyzing the pattern of age at first use of alcohol, cigarettes, and marijuana at the national level, then across all 50 States and the District of Columbia. Subsequently, the analysis was conducted using solely the eight largest States, where the sample sizes were large enough to statistically distinguish different patterns.

In the preceding discussions of initiation of cigarettes, alcohol, and marijuana (Chapters 2 to 4), the average age at first use was analyzed among persons who initiated use at age 25 or younger and during 1995 through 1997. These results are summarized in Table C.12.

The sequence of substance use initiation was examined from a number of different perspectives. First, the data were analyzed at the national level for the pattern of average ages at first use as defined in Chapters 2 to 4. Second, the analysis focused on a relatively narrow range of post-teen years, having allowed sufficient time for most young persons to have tried all three substances. Here, the analysis was limited to just those persons aged 20 to 25 in 1999, and all possible sequences of use of cigarettes, alcohol, and/or marijuana were enumerated.³ Third, the analysis was restricted to youths who recently initiated marijuana and focused on whether these youths all conformed to a similar pattern of first use of cigarettes, alcohol, and marijuana.

Also of interest was whether the first use of alcohol or cigarettes could be said to act as a "trigger" for subsequent first use of marijuana and whether the time between the first use of alcohol or cigarettes and the first use of marijuana is reasonably constant for most youths. Earlier work has established that youths who have used cigarettes are much more likely to use marijuana than youths who have not used cigarettes (Kandel & Yamaguchi, 1993; Kandel et al., 1992).

6.1 National Patterns

• The average age at first use of cigarettes was 15.0 (Table C.12). For alcohol, it was 15.7 years, and for marijuana, it was 16.2 years. Therefore, the national "pattern" of average age at first use was cigarettes first, then alcohol, and then marijuana.

Exhibit 6.1 Percentages Reporting Substance Sequence Patterns for the Use of Cigarettes, Alcohol, or Marijuana Among Persons Aged 20 to 25, by National Data: 1999

Note: Percentages may not sum to 100 due to rounding.

*In the group using one substance, 18.8 percent used only cigarettes or only alcohol and 0.2 percent used only marijuana.

Source: SAMHSA, Office of Applied Studies, National Household Survey on Drug Abuse, 1999 CAI.

The average national pattern, however, conceals a great variety of patterns of individual initiation of cigarettes, alcohol, and marijuana use, or combinations thereof (Tables C.13 and C.14, Exhibit 6.1). About 10 percent of persons aged 20 to 25 in 1999 reported they had never used any of the three substances, 19 percent reported having used only one of the substances, 27 percent reported having used exactly two of the substances, and the remaining 44 percent reported having used all three substances. So, although the largest single percentage (44 percent) had used all three substances (indicating a possible pattern of use of the three), most persons (56 percent) in that age range had only used two or fewer of the substances.

• About 19 percent had previously used only cigarettes or only alcohol, and most of those (16.2 percent) were alcohol-only users. Only 0.2 percent reported having ever used only marijuana. In other words, almost all of those who reported use of only one of those substances had used either alcohol or cigarettes and had not used marijuana. In this group, there was no "pattern" of transition from alcohol or cigarettes to marijuana. Instead, either alcohol or cigarettes represented the "final" stage.

• Of the 27 percent who reported past use of exactly two of the three substances, those who had used both alcohol and cigarettes, but not marijuana, constituted the majority combination (23.4 percent) (Table C.14). More persons (13.5 percent) reported having used cigarettes before alcohol than alcohol before cigarettes. The remaining 4.0 percent had used marijuana in combination with either cigarettes or alcohol. Approximately 3 percent had used either alcohol or cigarettes before marijuana, and 1 percent had used marijuana first. Therefore, the majority (23.4 of 27 percent) of persons aged 20 to 25 had used only alcohol and cigarettes and had not moved on to marijuana. For only 3 percent, there appeared to be a "pattern" of transition from alcohol or cigarettes to marijuana.

• Among those who had used all three substances (44 percent), the largest percentage (14.1 percent) reported having used cigarettes first, then alcohol, and then marijuana (Table C.15, Exhibit 6.1). Almost as many (12.7 percent) reported using alcohol first, then cigarettes, and then marijuana. The next two patterns were (a) cigarettes, then marijuana, then alcohol (6.1 percent) and (b) alcohol, then marijuana, then cigarettes (5.7 percent). The final two patterns were approximately equal in size, 2.4 percent each: (a) marijuana first, then alcohol, then cigarettes, and (b) marijuana first, then cigarettes, then alcohol (data not displayed in table or exhibit). Therefore, with respect to the group who had used all three substances, almost 5 percent of all persons aged 20 to 25 in 1999 had used marijuana before either alcohol or cigarettes, thus indicating no "pattern" in the expected direction. The remainder (about 39 percent) used either alcohol or cigarettes or both before marijuana. An estimated 32.5 percent had used alcohol before marijuana, with 32.9 percent using cigarettes before marijuana.

In summary, among persons aged 20 to 25 in 1999, there was great variation in the patterns of initiation of cigarettes, alcohol, and marijuana at the national level. An estimated 10.2 percent had never used any of the substances, and 42.2 percent had only used cigarettes or alcohol, or both. The remaining 47.5 percent had used marijuana, usually in some combination with alcohol or cigarettes or both. Overall, 32.9 percent had used cigarettes before marijuana, and a slightly smaller percentage (32.5 percent) had used alcohol before marijuana. Therefore, at the national level, neither cigarettes nor alcohol appeared to be a compelling "trigger" for subsequent marijuana use because over half (52.4 percent) reported never having used marijuana and only one third reported either starting with cigarettes and going on to marijuana or starting with alcohol and going on to marijuana.

6.2 State-Level Patterns

Tables C.13 and C.14 also present the percentages by State for each of the sequences of alcohol, cigarette, and marijuana use for persons aged 20 to 25 in 1999. Because the number of persons at the State level who indicated a particular pattern was often based on a small sample size, the confidence intervals for the percentages were quite large. Nevertheless, the estimates have been provided as a general indication of the variety of patterns across States. If the focus remains on the eight States with large populations (and samples), statistically significant differences in a number of the categories can be discerned.

• Not only were there significant differences among persons in the patterns of initiation at the national level, there also were differences among persons in the patterns of initiation among States. For example, 14.5 percent of persons aged 20 to 25 in California reported never having used alcohol, cigarettes, or marijuana, while only 6.6 percent in Michigan reported no use of these substances.

• Returning to look at State differences (Table C.12) in the average age at first use of alcohol, cigarettes, and marijuana among persons who first initiated those substances in 1995 to 1997 and were age 25 or younger at the time of initiation, the most common pattern was a national one: cigarettes first, then alcohol, and then marijuana. Forty-two (42) States conformed to the national pattern. Three States exhibited the alcohol, then cigarettes, then marijuana pattern, and five had the cigarettes, then marijuana, then alcohol pattern. Given that the samples in many States were quite small and that the confidence intervals for the three substances often overlapped, a number of States could easily show a different pattern in the full population. However, among the eight States with larger samples, the patterns could be distinguished. For example, in New York the average ages at first use for cigarettes and alcohol were similar and significantly lower than the average age at first use for marijuana. However, in Illinois there was no statistical difference between the average age at first use of alcohol and marijuana when compared with the national data.

Collectively, the evidence indicates that among the population aged 20 to 25 in 1999, there was no fixed pattern of progression from cigarettes or alcohol to marijuana at the national level. In fact, large percentages never used marijuana, or if they used it, they did not necessarily use it after having used cigarettes or alcohol. Nor did the patterns at the State level appear to be the same with respect to a fixed progression. Regarding State patterns in the average age at first use, different patterns are discernible in the States where the sample of respondents was relatively large. However, when talking about average age at first use for each of the three substances, the first users of one substance were not necessarily the same as the first users of another substance. A comparison of average ages does not represent an accurate picture of the sequencing of individual use.

6.3 Sequences Among Recent Initiates of Marijuana

Narrowing the focus to only those who had used marijuana can help to determine whether, at the individual level, first use of cigarettes or alcohol can be said to stimulate subsequent use of marijuana at a certain age or after a fixed period of time.

• Nationally, about 80 percent of all persons who initiated the use of marijuana in 1996 or 1997 at age 25 or younger had previously used either alcohol or cigarettes, or both (not shown in tables). This estimate is very similar to the percentage of persons aged 20 to 25 in 1999 who had used either cigarettes or alcohol, or both, before they first used marijuana (83.5 percent, Tables C.13 to C.15). The remainder had not previously used any alcohol and cigarettes. Therefore, cigarette or alcohol use cannot be said to be a universal trigger for marijuana initiation among youths because 20 percent of marijuana initiates either never first used alcohol or cigarettes before marijuana or started marijuana use before their first use of alcohol or cigarettes.

• The 80 percent could be divided into three groups: 8.6 percent had begun using only alcohol before marijuana, 16.2 percent had begun using only cigarettes first, and the majority-55.4 percent-had used both alcohol and cigarettes prior to their first marijuana use. Overall, therefore, 71.6 percent had initiated cigarettes before marijuana (about 64 percent had initiated alcohol before marijuana).

• The national average age at first use of marijuana was statistically different in the three groups. For those who used both alcohol and cigarettes first, the average age at first marijuana use was 16.9 (Table C.16). For the group who used cigarettes first, the average age at first marijuana use was 14.9 years (Table C.17). For the group who initiated alcohol first, the average age at first use of marijuana was 16.3 years (Table C.18).

• For the group who used both alcohol and cigarettes before marijuana, the average age at first use of cigarettes was 13.9 years, and the average age at first use of marijuana was 16.9 years, a lag of 3 years. However, for the group who used only cigarettes before marijuana, the average age at first use of cigarettes was only 13.0 years, and the average age at first use for marijuana was 14.9 years, a lag of about 2 years. The picture is similar with respect to alcohol and marijuana. Therefore, not only do the ages at first use for the same substance in the different subgroups differ significantly, but the lags between the average age at first cigarette or alcohol use vary as well. This would seem to indicate that the notion of a fixed age for the "trigger" substance and a fixed lag before marijuana use is not supported.

• Among the eight States with large samples, there were significant differences in the average age at first use and in the lag between cigarette and marijuana initiation (Tables C.16 to C.18). For example, New York reported the following average ages at first use for the group who initiated both alcohol and cigarettes before marijuana: alcohol, 13.6 years; cigarettes, 14.4 years; and marijuana, 17.3 years. Florida, by contrast, displayed the more typical pattern among large States, with an age at first use of cigarettes, 13.8 years, fairly close to the age at first use of alcohol, 14.1 years, and followed by marijuana, 16.7 years. Therefore, in addition to the average ages at first use and lags differing for the same substance in different subgroups of the national population, they also differ within the same subgroup among States.

• Not only did the average ages at first use differ among the three groups, but the average age profile at the time of interview for each group differed as well (Table C.19, Exhibit 6.2). The average current ages for those who used only alcohol before first use of marijuana was 19.4 years. The average current age for those who used only cigarettes before marijuana was 17.8 years. The average current age for those who used both alcohol and cigarettes before marijuana was 19.9 years.

Exhibit 6.2 Average Ages for Those Who Initiated Alcohol and/or Cigarette Use Before Marijuana Use, by Age in Years: 1999

Source: SAMHSA, Office of Applied Studies, National Household Survey on Drug Abuse, 1999 CAI.

There was no similarity in the paths from cigarettes (or alcohol) to first use of marijuana among recent initiates: (a) the average age at first use of cigarettes differed at the national level between the cigarette-only initiates (age 13.0) and the alcohol-and-cigarettes initiates (age 13.9); (b) the lag between first use of cigarettes and first use of marijuana differed between the cigarette-only group (1.9 years) and the cigarette-and-alcohol initiate group (3 years); (c) the age at first use and pattern of first use of alcohol, cigarettes, and marijuana varied across the large States; and (d) the age profiles of youths exhibiting the different sequences of the three substances differed as well.

As shown in Exhibit 6.2, the substance use profile for those who had initiated alcohol and/or cigarettes before marijuana was that they averaged 19.9 years of age in 1999 and reported first use of marijuana 3 years earlier in 1995 to 1997 at an average age of 16.9. This group had previously initiated both cigarettes and alcohol in 1992 to 1994 at the average age of about 14 (13.9 years for cigarettes and 14.0 years for alcohol). The group who initiated only cigarettes before marijuana had an average age of 17.8 in 1999, had initiated marijuana about 3 years earlier in 1995 to 1997 at an average age of 14.9, and had initiated cigarettes on average 2 years before that in 1993 to 1995 at an average age of 13.0. The group who initiated only alcohol before marijuana averaged 19.4 years of age in 1999, started using marijuana 3 years earlier in 1995 to 1997 at an average age of 16.3, and had previously started the use of alcohol about 2 years earlier in 1993 to 1995 at an average age of 14.4. Therefore, the substance initiation profile for these three groups was quite different in terms of average ages.

Finally, an examination of the raw data revealed that the distributions of the sequence of use among individuals within (and among) these three groups varied widely. Within the group of those who first used alcohol and cigarettes before their first use of marijuana, the lag between the first use of alcohol and first use of marijuana, or between the first use of cigarettes and first use of marijuana, varied widely-from no lag to lags of 17 years, depending on the substance and the youth's age. Approximately the same number of youths reported starting cigarettes and marijuana at age 12 as the number who reported starting cigarettes at age 11 and marijuana at age 12. However, for youths who began the use of marijuana at ages 13 through 22, a larger number had started to use cigarettes 1 to 2 years prior than the numbers who had started cigarettes and marijuana in the same year.

³ The choice of ages 20 to 25 was somewhat arbitrary; however, it was aimed at reflecting the majority of initiation for these substances and was based on the fact that relatively few persons initiate use after age 25. Among all persons in 1999 who reported ever having used marijuana, 81.3 percent had used it by age 20 and 92.9 percent had used it by age 25. For alcohol, the comparable percentages were 85.0 percent by age 20 and 96.6 percent by age 25. For cigarettes, the percentages were 92.0 and 97.8 percent, respectively. Therefore, this age group represents most of the initiates of all three substances.

This page was last updated on June 03, 2008.

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