1998 National Household Survey on Drug Abuse

Marijuana

Heroin

Cocaine and Crack Cocaine

Hallucinogens

Inhalants

Cigarettes

Alcohol

8. TRENDS IN INITIATION OF DRUG USE

Details of the methodology are available in Trends in the Incidence of Drug Use in the United States, 1919-1992, released in 1996. Briefly, the estimates are based on the NHSDA questions on age at first use. Using each respondent's reported age at first use in conjunction with his/her age and interview date, the respondent's year of first use of each drug was determined by subtracting their age from the interview year and then adding the age at first use. By combining all respondents and applying sample weights, estimates of the number of new users of each drug for each year were made. These estimates include new users at any age, including ages under 12. In addition, the average age of new users in each year and age-specific rates of first use were estimated. These rates are presented in this report as the number of new users per 1,000 person-years of exposure. The rates could also be described as the number of new users per 1,000 potential new users. The numerator of each rate is the number of persons in the age group who first used the drug in the year (times 1,000), while the denominator is the number of persons who were exposed to the risk of first use during the year, adjusted for their estimated exposure time (exposure time was expressed in years). Persons who first used the drug in a prior year have zero risk of first use in the current year, and persons who still have never used the drug by the end of the current year had one full year of exposure to risk. Persons who first used during the year are assumed to have a half year of exposure to risk.

The incidence estimates are based on retrospective reports of age at first drug use by survey respondents interviewed during 1994-98, and may therefore be subject to several biases, including bias due to differential mortality of users and nonusers of each drug, bias due to memory errors (recall decay and telescoping), and underreporting bias due to social acceptability and fear of disclosure. See Appendix 2, Section III for a discussion of these biases. As is explained in Appendix 2, it is possible that some of these biases, particularly telescoping and underreporting because of fear of disclosure, may be affecting estimates for the most recent years more significantly. However, further analysis is needed to show the magnitude of these biases.

Marijuana

° The rising incidence during 1991-1994 seems to have been fueled primarily by the increasing rate of new use among youth age 12-17 years (from 38.4 per 1,000 potential new users in 1991, to 72.8 per 1,000 potential new users in 1994). This is in contrast with the epidemic of the late 1960s and early 1970s, in which there were similar increases among young adults as well as youth, but with the rates among young adults dominating through 1972. The rates of marijuana initiation for youth leveled off during 1994-1996 at their highest levels ever since the early peak levels in the late 1970s. The 1997 rate for youth (64.4) was significantly lower than the 1996 rate (79.3)(Figure 13).

Heroin

° The rate of heroin initiation for the age group 12-17 increased from below 1.0 during the 1980's to 2.7 in 1996 and dropped to 1.1 in 1997. This apparent drop is not a statistically significant change and should be viewed with caution because of the small number of respondents that these estimates are based on and the potential impact of reporting errors for this rare and stigmatized behavior (Figure 14).

° A large proportion of the recent heroin initiates are young and are smoking, sniffing, or snorting heroin. Among recent initiates found in the 1997 and 1998 NHSDAs, 87 percent were under age 26 and 72 percent had never injected heroin. A similar analysis of new heroin users in the 1991 and 1992 NHSDAs showed that only 61 percent were younger than age 26 and only 46 percent had never injected (questions about smoking, snorting, and sniffing were not included in the NHSDA until 1993).

Cocaine and Crack Cocaine

° The rates of initiation among different age groups have been increasing in recent years. In particular, the rate among youths age 12-17 increased from 4.1 in 1991 to 10.8 in 1997; this rate in 1997 was similar to the high rates of the early 1980s. Historically, most initiation of cocaine use has taken place among young adults age 18-25. The rate for that age group fell from a high of 28.8 in 1982 to 9.8 in 1992. Initiation rates among this age group have increased to 15.9 in 1997 (Figure 15).

° The number of new crack cocaine users was 302,000 in 1997. While there has been little change in the overall number of new crack users per year since 1985, the age-specific rate of new use for age 12-17 years has steadily climbed from 1.2 in 1992 to 5.6 in 1997.

Hallucinogens

Inhalants

Cigarettes

° An estimated 2.1 million people began smoking on a daily basis in 1997. More than half of these new daily smokers were younger than age 18. This translates to more than 3,000 new youth smokers per day. The rate of youth initiation of daily smoking increased somewhat from 55.5 to 74.9 per 1,000 potential new users between 1991 and 1996, but remained level in 1997.

Alcohol

This page was last updated on June 01, 2008.

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