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1998 National Household Survey on Drug Abuse

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8. TRENDS IN INITIATION OF DRUG USE

Estimates of drug use incidence, or initiation, provide another measure of the Nation's drug problem. They can suggest emerging patterns of use, particularly among young people. In the past, increases and decreases in incidence have usually been followed by corresponding changes in the prevalence of use. In 1996, SAMHSA released a detailed report on incidence trends based on 1991-93 data, covering the period 1919 through 1992. Using the 1994 through 1998 NHSDA data, this section updates these earlier estimates and extends them to 1997.

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

An estimated 2.1 million Americans used marijuana for the first time in 1997. The number had increased from approximately 1.4 million in 1991 to 2.4 million in 1994, and has not changed significantly since 1994. The number of new marijuana users per year reached its highest level in 1975 (3.1 million). It is interesting to note that the decrease in prevalence of marijuana use that occurred in the 1980s did not begin to occur until several years after the peak in incidence.

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

There were an estimated 81,000 new heroin users in 1997, not statistically different than the 149,000 new users in 1996. Estimates of heroin incidence are subject to wide variability and usually do not show any clear trend, although there was a statistically significant upward trend in the number of new heroin users from 1992 to 1996, a finding that is consistent with anecdotal reports of increasing numbers of new heroin users. The recent increases in new heroin use are comparable to the increases seen in the epidemic of the late 1960s and early 1970s.

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 annual number of new users of any form of cocaine rose between 1991 and 1997 from 470,000 to 730,000. However, this was a lower level than during the early and mid-1980s. Recent initiation was at a lower rate than it was in 1980-1986, when the number of new initiates ranged from 1.1 to 1.4 million per year.

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

There were an estimated 1.1 million new hallucinogen users in 1997, nearly twice the average annual number during the 1980s. The rate of initiation among youths age 12-17 increased between 1991 and 1995, from 11.1 to 25.0 per 1,000 potential new users. Over the same period, the rate for ages 18-25 years rose from 13.1 to 22.9. Both age groups had constant rates during 1995-1997.

Inhalants

There were an estimated 708,000 new inhalant users in 1997, up from 332,000 in 1989. The rate of first use among youths age 12-17 rose significantly from 1989 to 1995, from 8.4 to 18.8 per 1,000 potential new users, and remained level after that. For young adults age 18-25, there was an increase in the rate of first use between 1989 and 1996 (from 3.7 to 10.7 per 1,000 potential new users) and a leveling off in 1997 (9.2 per 1,000 potential new users).

Cigarettes

An estimated 3.1 million people tried their first cigarette in 1996 (1997 estimate not available). The rate of initiation among youths age 12-17 increased from 98.9 to 146.2 per 1,000 potential new users between 1991 and 1995, and remained level in 1996.

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

In 1996 there were approximately 4.2 million new users of alcohol, compared with about 3.4 million new users in 1991. The rate of new usage of alcohol among the 18-25 age group has begun to rise in recent years (164.5 per 1,000 potential new users in 1989, compared with 219.0 per 1,000 potential new users in 1996). In addition, the rate of initiation of alcohol use among the 12-17 age group increased from 111.0 per 1,000 potential new users to 158.8 over the same period.

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This page was last updated on June 01, 2008.