Address correspondence to :
Catherine Tang, Ph.D.
Chinese University of Hong Kong
Department of Psychology
Shatin, NT, Hong Kong
Running head: Occasional and regular drug users
Data on marijuana and heroin use were obtained from 969 adolescents in Hong Kong, part of them being offenders. Very high drug use prevalence rates were found which is due to the unique population studied. All but two of the heroin users were incarcerated youth. Drug use frequencies were highly associated with psychosocial variables such as sensation seeking, peer drug use, family drug use, susceptibility to peer pressure, perceived control to gain access to drugs, intention to try other substances, and perceived adverse consequences of drug use. Interactions were found indicating, for example, that regularly marijuana using girls and occasionally heroin using girls were characterized by higher levels of sensation seeking and susceptibility to peer pressure than their male counterparts. Polysubstance use was generally related to high levels of psychosocial vulnerability factors. The exclusive use of marijuana was associated with high susceptibility to peer pressure and with perceived control to gain access to drugs. The findings reflect a complex interplay of psychosocial variables with substance use in adolescents which, however, cannot be generalized beyond this particular sample in Hong Kong.
Keywords:
drug use, adolescents, delinquents, sensation seeking, peer pressure, social influence, heroin, marijuana
Adolescent substance use is seen as being determined by various factors in the person and in the environment. Psychological causes and effects of illicit drug use among adolescents have been studied intensively (For a recent account see Baer, Marlatt, & McMahon, 1993; Maton & Zimmerman, 1992; Smith & Nutbeam, 1992; Vega, Gil, & Zimmerman, 1993; Zane & Sasao, 1992; Zimmerman & Maton, 1992). Research provides evidence that drug use is associated with personality traits such as sensation seeking, and with social influence variables such as family drug use, peer drug use, and peer pressure to try substances (Bentler, 1992; Botvin et al., 1992; Farrell, Danish, & Howard, 1992; Goddard, 1992; Hammersley, Lavelle, & Forsyth, 1992a; 1992b; McNeill, 1992; Newcomb & Felix-Ortiz, 1992; Zuckerman, 1979). The present research contributes to this evidence by providing new data from Hong Kong .
The personality disposition of sensation seeking (or the closely related construct of disinhibition) has been found to be related to some deviant behaviors including drug abuse (Andrucci, Archer, Pancoast, & Gordon, 1989; Newcomb & Bentler, 1988a, 1988b; Watson & Clark, 1993; Zuckerman, 1979). This trait is defined as a need for varied, novel, and complex sensations and experiences and the willingness to take physical and social risks for the sake of such experiences (Zuckerman, 1971, 1991). Some individuals are more likely to violate the moral or legal rules of the society in order to pursue a pleasure-oriented lifestyle. They attend to their feelings here and now without contemplating future risks for themselves or others. These individuals display a 'behavioral disinhibition' as opposed to those who are more 'constrained' or self-controlled (Watson & Clark, 1993). The former reflects a spontaneous and impulsive approach to life neglecting long-term consequences of risky actions. The latter describes persons who feel bound to the rules and expectancies of their culture and who rather tend to delay gratifications to attain desirable long-term goals or social rewards. They are more dependable and self-disciplined by committing themselves to generally accepted standards and by avoiding dangerous situations. This personality dichotomy is similar to the notion of being overcontrolled versus undercontrolled. In a study to validate a new disinhibition scale, the following correlations with other variables emerged: impulsivity (.68), irresponsibility (.63), risk taking (.59), low persistence (.56), playfulness (.54), norm rejection (.49), danger seeking (.47), and experience seeking (.47) (Watson & Clark, 1993, p. 512). In a study with 901 university students, the following correlations between disinhibition and drug use were obtained: alcohol (.44), marijuana (.33), cigarettes (.29), psychedelics (.26), narcotics (.19), and tranquillizers (.12) (Watson & Clark, 1993, p. 517). Boys scored generally higher on disinhibition than girls. Zuckerman's (1979) Sensation Seeking Scale that includes the four subscales of Experience Seeking, Thrill/Adventure Seeking, Disinhibition, and Boredom Susceptibility was typically the most powerful predictor of substance use and abuse out of five self-report measures in predicting drug use (Jaffe & Archer, 1987). All four Sensation Seeking subscales were positively correlated with licit and illicit drug use for females, and all the subscales except Experience Seeking correlated with licit drug use for males, whereas Disinhibition was associated with illicit drug use for males (Newcomb & McGee, 1991). Barnea, Teichman and Rahav (1992) found that sensation seeking was the only personality trait that predicted substance use. It had a strong direct as well as indirect effect on drug use, on behavioral intentions, and on attitudes toward drugs. Stacy, Newcomb and Bentler (1993) found that sensation seeking predicted alcohol use over a nine-year period.
Social influence is commonly regarded as the most conspicuous factor in the development of drug taking. Adolescents face a number of developmental tasks to prove themselves in their reference groups (Jessor, 1987, 1993; Yu & Williford, 1992). If the dominant reference group mainly consists of peers who value drug use as an 'adult behavior' or as indicators of maturity and independence from parents, then the individual attempts to meet these expectations. There may be role conflict, for example, when the family norms contradict the peer group norms, and it may take an extended period of time until the youngster eventually complies with one or the other. Kandel (1980) concluded that peer related factors, e.g., the extent of perceived drug use in the peer group, self-reported drug use by peers, and perceived tolerance for use, are consistently the strongest predictors of subsequent alcohol and marijuana use, even when other factors are controlled. Barnea et al. (1992) found that peer influence on adolescent substance use was more significant than that of parents. Peers' drug use behavior had a direct effect both on adolescents' drug use and on their behavioral intentions. Perceived peer attitudes had a strong effect on adolescents' drug related attitudes and on their actual drug use (see also Hansell & Mechanic, 1990; Iannotti & Bush, 1992; Stacy, Newcomb, & Bentler, 1992, 1993; Stanton & Silva, 1992). Peer norms regarding substance use, considered alone, are also positively related to adolescents' use of substances (e.g,. Donovan & Jessor, 1978, 1985; Ellickson & Hays, 1992; Newcomb, Maddahian, Skager, & Bentler, 1987). Biddle, Bank and Marlin (1980) found in a path analysis that peer norms regarding alcohol use had a significant direct effect on the students' own norms, which in turn had a significant direct effect on the students' frequency of alcohol use. This has been recently replicated by another path analysis by Webster, Hunter and Keats (1994). Newcomb et al. (1987) found peer norms to be the most highly correlated out of 12 risk factors with a composite substance use score. Susceptibility to peer pressure may be considered either a social influence variable or a personality trait. It has been proposed that more socially oriented students are more sensitive to social evaluations and hence more susceptible to conformity or social image pressures (Botvin & McAlister, 1981). Dielman, Butchart, Shope and Miller (1990) confirmed and extended the results of earlier studies, indicating that peer alcohol use and peer norms regarding alcohol use, in combination with susceptibility to peer pressure, accounted for most of the variance in adolescent alcohol consumption. Susceptibility to peer pressure emerged as the most important predictor of both adolescent alcohol use and misuse. Dielman, Campanelli, Shope and Butchart (1987) found that susceptibility to peer pressure was more highly correlated with all substance use, misuse and intention items than were self-esteem and health locus of control. A conceptual model proposed by Dielman et al. (1990) claims that early childhood exposure to deviant parental norms (e.g., tolerance of adolescent substance use) and behavior with respect to substance use (e.g., immoderate alcohol use or use of illicit drugs) increased the child's tolerance of deviant behavior, which in turn led to increased susceptibility to peer pressure as well as to attraction to peer groups with deviant norms and behaviors. Increased exposure to deviant peer norms and behavior in combination with increased susceptibility to peer pressure was then hypothesized to result in a greater likelihood of the adolescent's adoption of deviant norms and drug-use behaviors (see also Alberts, Hecht, Miller-Rassulo, & Krizek, 1992; Rose, Bearden, & Teel, 1992).
This study not only aims at surveying the frequencies of marijuana and heroin use of girls and boys in Hong Kong. A distinction is made between occasional and regular marijuana and heroin users. It is to be examined whether these groups differ in personality and social influence variables. A straightforward hypothesis is that all psychosocial vulnerability factors or predispositions are linearly related to frequencies of substance use. A differential hypothesis claims that this relationship also depends on other factors such as gender. Girls and boys might differ in psychosocial terms at different levels of drug use frequency. Moreover, synergistic effects might occur when adolescents combine the use of two illicit substances.
A sample of 1,001 Chinese adolescents was contacted. Thirty two of the questionnaires (3.1%) were discarded for participants' insincere test taking behavior, obvious response sets, or leaving blank most of the questions. Finally, 969 valid questionnaires were retained for data analysis. Among these 969 participants, more than half were normal secondary school students attending Form 2 to Form 6 in two schools. One of the schools was classified by the Education Department as around the "Band Four" to "Band Five" school, i.e., students' academic performance was among the poorest in Hong Kong. Another was a "Band Two" school, where students' academic performance was about average to high average.
The second sample consisted of incarcerated delinquents. Four facilities of the Correctional Services Department were approached. Almost all of the young offenders in these facilities, who were eligible to read and had about Primary 6 education level, participated in the data collection. Three Correctional Homes of the Social Welfare Department were also approached.Written consent from both participants and their parents was obtained. Response rates were between 30% and 40%.
Most of the participants (59.8%, N=579) were school students and 40.2% (N=390) were incarcerated delinquents. Among the school students, 39.2% (N=277) were boys and 60.8% were girls (N=352). In the delinquent sample, 77.4% (N=302) were boys and 22.6% (N=88) were girls. Chi-square analysis confirmed significant differences. More girls were in the school sample whereas more boys were in the delinquent sample.
The mean age of the school sample was 15.87 years (SD=1.75), 15.91 years for boys and 15.84 years for girls whereas in the delinquent sample, the overall mean age was 17.32 years (SD=1.75). On average, delinquent boys were 17.28 years, and girls were 17.43 years of age. There was no sex by institution interaction (F[1,961]=.73, p>.05), or main effect of sex (F([,961].000, p>.05) on age. However, age differences were significant between the school and delinquent teenagers (F[1,961]=136.54, p<.001).
Drug Use Behavior. Frequency of marijuana and heroin use measures were adapted from Segal (1990). Frequency of drug use over the preceding six months was rated on 7-point scales anchored with Never (1), Less than once a month (2), Two or three times a month (3), Once a week (4), 2-5 times a week (5), Once a day (6), More than once a day (7).
Peer Drug Use. Following Stein, Newcomb and Bentler's (1987) format in assessing peer drug use, participants were asked how many of their good friends used illicit substances at least once a month on a 5-point scale that ranged from None (1), One to Two of them (2), Some of them (3), Most of them (4) to All (5): (a) How many of your good friends used heroin at least once a month? (b) How many of your good friends used other illicit substances at least once a month ('pills', cannabis, cough medicine, or organic solvents) ?
Family Drug Use. It was asked how frequent parents or other family members (e.g., siblings) take one of the following substances. If there was more than one person, the one with the highest drug use was to be chosen: (a) heroin, (b) other illicit substances ('pills', cannabis, cough medicine, or organic solvents). The seven frequency levels were the same as those above for one's own drug use.
Susceptibility to peer pressure. An eight-item scale on perceived susceptibility to peer pressure by Dielman et al. (1987) was used (e.g., 'If a friend offers you a drink of alcohol, would you drink it?'). Participants were asked how far they agreed on a four-point scale anchored Strongly Disagree (1), Disagree (2), Agree (3), Strongly Agree (4) (Cronbach's a = .80).
Sensation seeking. As a measure of this personality trait, Zuckerman's (1971, 1979) Sensation Seeking Scale in the version of Huba, Newcomb, and Bentler (1981) was chosen. The 16-item scale included four subscales, namely Experience Seeking, Thrill/Adventure Seeking, Disinhibition, and Boredom Susceptibility with items such as 'I enjoy watching many of the "sexy" scenes in movies'. Participants answered on a four-point scale anchored Strongly Disagree (1), Disagree (2), Agree (3), Strongly Agree (4) (Cronbach's a = .67).
Perceived control over access to drugs. Participants' perceived control to gain access to drugs were assessed by two items on how easy they could obtain illicit substances, based on a four-point scale ranging from Very Easy (1), Easy (2), Difficult (3) to Very Difficult (4) : (a) How far do you find it easy to obtain heroin? (b) How far do you find it easy to obtain other illicit substances?
Intention to use drugs if they were licit. Intention to use drugs was assessed by asking two items on how likely participants would use (a) heroin and (b) other illicit substances if they became licit, based on a five-point scale anchored with Definitely Will (1), Very Likely Will (2), Mabe (3), Very Unlikely (4), and Definitely Will Not (5).
Adverse Consequences of Drug Use. Participants were asked four items on how often they had been negatively affected by drug use over the preceding six months: (a) How far did your using alcohol or other illicit substances affect your working/ academic performance? (b) How far did your using alcohol or other illicit substances affect your family life? (c) How far did your using alcohol or other illicit substances affect your social or recreational activities? (d) How far did your using alcohol or other illicit substances affect situations in which use is physically hazardous, e.g., driving while being intoxicated? (Cronbach's a = .91).
Self-report questionnaires written in Chinese with items on demographic variables and the above mentioned measures were administered in group format by reading a standardized instruction. Participants were assured that their responses would be completely confidential and would not be revealed to parents, school or institution personnel. The data collection took place from November 1993 to February 1994. On average, completion of the questionnaire took about 30 minutes.
Table 1 displays the reported frequencies of drug use within the last six months before the survey. As expected, the majority of the adolescents did not report any use of marijuana or heroin. However, the prevalence rate was still very high in this sample which is due to the fact that 40% of them were incarcerated offenders with various problem behaviors. All but two of the heroin users were incarcerated.
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The frequency distributions differ for the two drugs. There were 151 regular heroin users who took the substance more than once a day whereas there were only 39 who did the same with marijuana. For further analyses, the distributions were trichotomized into non-users, occasional users, and regular users. For heroin, all who reported having used it 'more than once a day' were considered to be regular users. The five classes below were collapsed into the category of occasional users. For marijuana, the classes 'less than once a month' and '2 or 3 times a month' were collapsed to establish the category of occasional users while those with more frequent abuse were seen as regular users. Thus, substance-specific definitions of what represents an occasional or a regular user have been applied.
The next section will deal with marijuana use and its psychosocial correlates. Subsequently, heroin use will be explored. Then, polysubstance use will be analyzed. Finally, overall correlations between substance use and psychosocial variables will be presented.
A series of two-way analyses of variance with marijuana use and gender as factors were conducted. Sensation seeking differed between non-users and users of marijuana with regular users attaining the highest levels (F[2,848]=32.35, p < .01). There was an interaction between marijuana and gender (F[2,848]=7.79, p < .01). Among those who stayed abstinent, boys scored significantly higher on sensation seeking than girls which was expected. However, among the regular marijuana users, girls may even score somewhat higher although this was not significant (Figure 1).
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For susceptibility to peer pressure, a similar pattern emerged. A main effect for marijuana use was found (F[2,848]=211.21, p < .01), no effect for gender but a disordinal interaction (F[2,848]=5.90, p < .01). Abstinent boys were more susceptible than girls (t=5.04), although at a very low level, whereas among regular users, girls attained higher values than boys (t=1.88, p < .02, one-tailed) (Figure 2).
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Drug use by family members ('pills', cannabis, cough medicine, or organic solvents) was higher among marijuana using adolescents than abstinents (F[2,848]=44.27, p < .01), in particular among girls as indicated by an interaction effect (F[2,848]=9.22, p < .01). There was also a main effect for gender (F[1,848]=5.52, p < .02). Adolescent girls who took marijuana at least once per week had a family background where a parent or another relative used drugs more than once per month (Figure 3).
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Drug use by peers ('pills', cannabis, cough medicine, or organic solvents) was very much higher among marijuana using adolescents than among abstinents (F[2,848]=404.73, p < .01). There was no effect for gender and no interaction between gender and habit.
Perceived control over access to drugs was very much lower among abstinent youths than among marijuana users (F[2,848]=303.37, p < .01) but the interaction shows that in particular occasional marijuana using girls and regularly marijuana using boys found it most easy to obtain drugs (F[2,848]=6.36, p < .01). There was no difference between occasional and regular marijuana users in their control over access to drugs.
Adverse consequences were related to the amount of marijuana use (F[2,848]=252.29, p < .01) but there was also an interaction (F[2,848]=8.18, p < .01). Girls who occasionally used marijuana reported the highest levels of adverse consequences (Figure 4).
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Finally, it was found that the intention to try heroin if it were licit was much higher among marijuana users than among the abstinent (F[2,848]=179.69, p < .01). The highest intention was found for regular female marijuana users, as indicated by a borderline interaction effect (F[2,848]=2.86, p < .06).
Another series of two-way ANOVAs with heroin use and gender as factors were conducted. Sensation seeking differed between non-users and users of heroin (F[2,835]=18.54, p < .01). There was an interaction between heroin use pattern and gender (F[2,835]=10.36, p < .01). Among those who remained abstinent, boys scored significantly higher on sensation seeking than girls which is in line with the literature. However, among the heroin users, girls who took heroin occasionally stood out with the highest sensation seeking values (Figure 5).
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For susceptibility to peer pressure, a similar pattern emerged. A main effect for heroin use was found (F[2,835]=147.11, p < .01), no effect for gender but an interaction (F[2,835]=7.04, p < .01). Abstinent boys were more susceptible than girls (t=5.5), although at a very low level, whereas among occasional users, girls attained higher scores than boys (t=1.95, p = .05) (Figure 6).
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Heroin use by family members was higher among heroin using adolescents than among abstinents (F[2,835]=42.77, p < .01), but there was no interaction or gender main effect. Adolescents who took heroin more than once per day had a family background where a parent or another relative used heroin less than once per month.
Heroin use by peers was very much higher among heroin using adolescents than among abstinents (F[2,835]=535.83, p < .01). There was an interaction indicating that heroin abusing girls tend to perceive more peer heroin models than their male counterparts whereas abstinent girls did less so than boys (F[2,835]=5.53, p < .01).
Perceived control over access to drugs was very much lower among abstinent youths than among heroin users (F[2,835]=249.14, p < .01) but the interaction shows that this was in particular true for the girls (F[2,835]=7.90, p < .01). There was no difference between occasional and regular heroin users in their control over access to drugs.
Adverse consequences were related to the amount of heroin use (F[2,835]=368.98, p < .01) and there was no interaction. The more the adolescents took heroin the more they perceived problems in their daily life.
Finally, it was found that the intention to try other drugs if they were licit ('pills', cannabis, cough medicine, or organic solvents) was higher among heroin users than among the abstinent (F[2,835]=151.34, p < .01). The highest intention was found for occasional female heroin users, as indicated by an interaction effect (F[2,835]=6.16, p < .01).
A further question was to what degree adolescents used more than one of the two substances, and whether there were synergistic effects in terms of psychosocial variables. Table 2 represents a crosstabulation of the sample subdivided for frequency of marijuana and heroin use. Of the 951 adolescents without missing values, 626 reported never using marijuana or heroin whereas 49 were classified as being regular users of both substances. Of the 688 who never used heroin were 25 who used marijuana less than four times per month and 37 who used marijuana at least twice a week. Of the 151 who used heroin more than once a day were 30 who never used marijuana.
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A series of two-way ANOVAs were conducted to study the joint relationship of using both substances with psychosocial variables. Heroin use and marijuana use were chosen as factors, as shown in Table 2. Because of small cell sizes, gender or other factors could not be included. Both factors had highly significant main effects on all the psychosocial variables which replicates what had been found in the previous analyses. Moreover, there were interactions between marijuana and heroin use on all dependent variables except sensation seeking.
For susceptibility to peer pressure, an interaction (F[4,819]=7.76, p < .01) indicated that those who never used either marijuana or heroin attained a very low level whereas those who used marijuana regularly had the highest levels, independent of their heroin use (Figure 7).
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Perceived control over access to drugs was very low among youths who never used any of the two substances. An interaction was found (F[4,819]=11.91, p < .01) that indicated how the experience with one of the two drugs supported the perception of gaining control over access to illicit substances (Figure 8).
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The other interactions were in a similar manner, underscoring a synergistic effect. Using more than one substance is more closely related to a number of psychosocial variables. This kind of interaction was also found for Drug use by family members (F[4,819]=3.93, p < .01), Drug use by peers (F[4,819]=3.97, p < .01), Adverse consequences (F[4,819]=10.88, p < .01), and the Intention to try other drugs if they were licit (F[4,819]=2.74, p < .03). It was found that polysubstance use was more closely associated with psychosocial variables than monosubstance use.
Social influence is commonly regarded as the most important source of deviant behaviors. In line with this assumption there were close relationships between marijuana and heroin use and social influence variables in the present data set. The correlations (Table 3) between perceived peer drug use and marijuana use were .59 for boys and .73 for girls, respectively. The correlations between perceived peer drug use and heroin use were .63 for boys and .72 for girls, respectively. In other words, drugs were probably taken as part of social acitivities within a peer group.
Susceptibility to peer pressure which can be seen as a predisposition to drug use was also closely related to marijuana use (.50) and heroin use (.49) in boys, and to marijuana (.53) and heroin use (.46) in girls.
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Similarly high was the association between perceived control over access to drugs and marijuana use (.54 for boys, .56 for girls) and heroin use (.57 for boys, .62 for girls). Family drug use was only weakly related to marijuana use (.18) and heroin use (.20) in the male subsample, considerably higher, however, in the female subsample (.44 and .35, respectively). Sensation seeking as a personality disposition was obviously of less importance in this context (.19 for marijuana use and .14 for heroin use in boys, .32 for marijuana and .22 for heroin use in girls).
It is of note that the adverse consequences of drug use and the intention to try other drugs ware also closely related to marijuana and heroin use.
The present study has surveyed the use of marijuana and heroin of adolescents in Hong Kong and has explored the role that psychosocial factors may play in the adoption or maintenance of such deviant behaviors. The sample is unique because 40% were incarcerated offenders, many with multiple problem behaviors including drug-related violations. This explains the high prevalence rate of marijuana and heroin use. In particular, there were 151 of the 969 youths who took heroin more than once a day which constitutes a highly problematic subsample. Half of them were also occasional marijuana users, and one third of them used marijuana regularly.
This study confirms previous research on adolescent drug use and corroborates the role that social influence plays in the use of illicit substances. Very high correlations between perceived peer drug use, susceptibility to peer pressure, and control over access to drugs, on the one hand, and marijuana and heroin use, on the other, were found which underscores that substance use in adolescents may be interpreted as a social behavior that is developed and maintained in deviant peer reference groups. It was also found that the girls' drug use was more closely related to family drug use than it was for boys' drug use (see Table 3 and Figure 3).
The main findings aim on interactions between gender and frequencies of marijuana and heroin use. The personality trait of sensation seeking was positively related to drug use; it was also higher for non-using boys than for non-using girls which confirms previous findings (Andrucci et al., 1989; Barnea et al., 1992; Stacy et al., 1993; Watson & Clark, 1993; Zuckerman, 1979). An interaction between gender and marijuana use, however, pointed to higher sensation seeking scores for regularly marijuana using girls than for boys (see Figure 1). Another interaction between gender and heroin use, pointed to higher sensation seeking levels for occasionally heroin using girls than for boys (see Figure 5). The girls may have different motives for using substances, or they may be at an earlier stage in their drug using career where they are more pleasure-oriented and experimenting instead of being clinically addicted. They seem to be more driven by a need to adhere to a risky, wild and entertaining lifestyle while using drugs whereas the boys may be addicted and suffering. This is corroborated by the higher correlations between drug use and adverse consequences in the boys than in the girls (see Table 3). An indication of the desire to experience even more excitement was given by the question whether they would like to try other substances. The occasionally marijuana and heroin using girls reported the highest intentions to try other substances.
A similar interaction was found between gender and substance use, with susceptibility to peer pressure as the dependent variable. Again, regularly marijuana using girls (see Figure 2) and occasionally heroin using girls (see Figure 6) had the highest levels in this vulnerability factor along with the highest levels of adverse consequences of drug use. It is possible that these girls live in a social context where deviant amusements are commonplace and where it is difficult to resist social influence. Anecdotal evidence suggests that many of them have held jobs of prostitutes or waitresses in the red-light districts of Hong Kong where they were exposed to various deviant behaviors including polysubstance use. In addition, they earned enough to be able to afford drugs. It is of note that the occasionally marijuana using girls and all heroin using adolescents found it very easy to get access to drugs. It is possible that these young women got into their lifestyle partly by their sensation seeking or inclination to take chances but that, over time, they suffered from social pressures and adverse consequences.
By looking at the joint effects of marijuana use and heroin use on psychosocial variables, a synergistic pattern of polysubstance use emerged. Never taking any of these drugs was generally associated with a very low level of predisposing personality or social factors while using both drugs was associated with the highest level. Interestingly, if adolescents use marijuana regularly they are highly susceptible to peer pressure and gain control over access to drugs, no matter whether they take heroin in addition or not. This could mean that they have the prerequisites for a drug-addict career which is supported by the fact that most of them feel inclined to try heroin, if it were legally available. Unfortunately, the present data do not allow further examination of the question whether marijuana use represents a gateway for later heroin use.
The study has shed some light on adolescent drug use frequency and related psychosocial factors. But there are some limitations in this research that have to be pointed out to interpret the results with caution. Firstly, this is a cross-sectional study that does not allow to make any causal inferences. Longitudinal studies and those including interventions would be preferable. Secondly, the data are self-report data. There is no validation of drug use by physiological methods, observation, or peer ratings (cf. Anglin, Hser, & Chou, 1993; Belkin & Miller, 1992; Skog, 1992; Wagenaar et al., 1993). This is difficult to perform, in particular with such large samples, without compromising anonymity. Studies with higher internal validity should be designed to complement this kind of large-scale field studies. Thirdly, it might be considered to use alternative measures to those employed here to see whether the operationalization affects the results. Fourth, additional constructs should be included that have been proven useful in research on risk behaviors such as perceived self-efficacy to resist peer pressure or to refrain from risk behaviors (Bandura, 1992; Marlatt, Baer, & Quigley, 1994; Schwarzer, 1992, 1994). In sum, the present study has pointed to important personality antecedents and social influence factors that account for differences between regular and occasional drug users. Further studies should be launched to allow for more fine-grained analyses.
Figure 1
Interaction between frequency of marijuana use and gender on sensation seeking
Figure 2
Interaction between frequency of marijuana use and gender on susceptibility to peer pressure
Figure 3
Interaction between frequency of marijuana use and gender on family drug use
Figure 4
Interaction between frequency of marijuana use and gender on adverse consequences
Figure 5
Interaction between frequency of heroin use and gender on sensation seeking
Figure 6
Interaction between frequency of heroin use and gender on susceptibility to peer pressure
Figure 7
Interaction between frequency of marijuana use and heroin use on susceptibility to peer pressure
Figure 8
Interaction between frequency of marijuana use and heroin use on perceived control over access to drugs