NIDA Research Priorities and Highlights

Role of Research

Fetal and Childhood Development

The impact of drug abuse and addiction on our Nation's children is particularly onerous. Today, NIDA estimates that 5.5 percent of women use some illicit drug during pregnancy, translating into approximately 221,000 babies who have the potential to be born drug exposed. The full extent of the effects of prenatal drug exposure on a child is still not known completely, but science has shown that babies born to mothers who use drugs during pregnancy are often delivered prematurely, have low birth weights and smaller head circumferences, and are often shorter in length than infants not exposed in utero to drugs. Estimating the full extent of the consequences of maternal drug use is difficult, and determining the specific hazard of a particular drug to the unborn child is even more problematic given that typically more than one substance is used.

Although it is difficult, researchers are making progress in resolving these questions. For example, one group of investigators has demonstrated that there are cocaine receptors in the brains of fetal rats and that cocaine will bind to these brain sites. Such binding could be a mechanism by which cocaine could modify brain development and later behavior through modification of brain activity during fetal development. With this new information, researchers may be able to pinpoint the specific sites in the developing brain that are most vulnerable to cocaine and to develop better treatment strategies for prenatal cocaine exposure.

Drug use can also have a significant negative impact on the health of children who are exposed to nicotine or illegal drugs by growing up in a household where drugs and tobacco are abused. In addition, the use of drugs during childhood and adolescence can be particularly damaging to the child's developing body and psyche.

Participants at a NIDA-sponsored conference recently concluded that many childhood psychiatric disorders are strongly associated with subsequent substance use, although a causal role remains to be established. Furthermore, the meeting participants stressed that because other biological and environmental influences can increase or reduce the risk of drug use, the mere existence of a specific psychiatric disorder does not predestine a child to later drug use. However, research has shown that conduct disorder and anxiety disorders are more clearly associated than other disorders with later drug use. Bipolar (manic-depressive) disorder may constitute a risk factor, depression in the presence of another disorder may increase risk, and some subtypes of ADHD may also increase risk. The coexistence of more than one childhood psychiatric disorder has been found to greatly increase the risk for later drug use.

Effects of Maternal Drug Use

Recent results from a longitudinal study add to the growing body of evidence for the importance of studying the amount of exposure when examining developmental outcomes associated with use of drugs during pregnancy. Although there were no overall differences between mothers who used drugs and those who did not on gestational age, birth weight, or birth length, there was a significant relationship between the amount of cocaine used in the third trimester and newborn length and head circumference. Similarly, the reported amount of cocaine use in the third trimester was negatively associated with measures of state regulation, alertness, and the ability of the infant to orient to the environment. These findings raise concerns about later developmental abilities of these infants. [52]

Another study examined the effects of maternal substance use on the costs to neonatal care. The findings from this investigation suggest that exposure to drugs in newborns resulted in total hospital charges almost double those of nonexposed newborns. The results demonstrated a consistent pattern of effects on charges, mortality, and resource use in the hospital of drug-exposed newborns due, in part, to longer lengths of stay and higher intensity care per day. The investigators suggest that their results confirm the policy concern that maternal substance use has severe consequences for the baby's health and that these costs are often borne by others. [53]

What might be the effect of prenatal drug exposure on the child's development? Children with histories of prenatal polydrug exposure that included cocaine scored significantly lower on standardized test measures of language development than nonexposed children, according to one group of investigators. Nearly half of the children in the drug-exposed group qualified for early intervention services. Significant differences between groups were also noted on measures of infant development. All the children studied were living in stable, drug-free environments at the time of the study. Nevertheless, the results indicate that, due to the cumulative effects of prenatal history, children with histories of prenatal drug exposure should be considered at risk for language delay. [54]

Cocaine's Effects on the Developing Brain

In September 1997, the New York Academy of Sciences, with support from NIDA, held a landmark conference titled "Cocaine: Effects on the Developing Brain." This was the first time that basic and clinical investigators had come together to discuss what is and is not known about the developmental consequences of prenatal cocaine exposure. Much of the research reported at this meeting came from longitudinal studies that NIDA has been supporting. For example, since 1991 NIDA has been a cosponsor, with the National Institute on Child Health and Human Development, Center for Substance Abuse Treatment, and Administration for Children and Families, of the Maternal Lifestyles Study (MLS), which has been examining the health and developmental consequences of illicit drug exposure during pregnancy in 1,400 children, who will be followed into their school years, when problems of learning disabilities, hyperactivity, and emotional disorders tend to emerge.

So far, analysis of the data from the MLS has shown that exposure to cocaine during fetal development may lead to subtle but significant deficits later on, especially with behaviors that are crucial to success in the classroom, such as blocking out distractions and concentrating for long periods. Other studies are also showing subtle cognitive and learning problems in some middle school children who were exposed to cocaine before birth.

Childhood and Adolescent Development

NIDA has spent, and continues to spend, significant effort studying the factors that put children at risk for later drug use to develop new interventions. One recent study, for example, attempted to identify developmental correlates of alcohol and tobacco use among elementary school children. Children's current alcohol and tobacco use was strongly related to low scores of several measures of child competence, both self-report and teacher rated. Use of these substances was also associated with less effective parenting behaviors and with parental use of alcohol and tobacco. The researchers conclude that children's early experiences with tobacco and alcohol are associated with weak competence development and exposure to socializing factors that promote risk taking. [55]

Another group of investigators examined the childhood, early adolescent, and late adolescent predictors of young adult drug use and delinquency to explore the effects of drug use on delinquent behavior. Data on childhood aggression, early and late adolescent drug use and delinquency, and young adult drug use and delinquency were gathered during the course of a 20-year longitudinal study of children. Overall, the results were consistent, with drug use and delinquency during early and late adolescence serving as the mediator between childhood aggression and young adult drug use. Adolescent drug use was associated with later delinquency. The findings indicated that childhood aggression was related to both young adult drug use and delinquency. In addition, there was stability of drug use and delinquency between early adolescence and young adulthood, and drug use during early adolescence had an impact on delinquency not only in early adolescence but also in late adolescence and young adulthood. The findings suggest that a decrease in drug use during adolescence should decrease delinquency in early and late adolescence and in young adulthood. [56]

Previous research has noted that schools vary in substance use prevalence rates, but explanations for school differences have received little empirical attention. To examine this issue, investigators assessed variability across 36 elementary schools in rates of early adolescent alcohol, cigarette, and marijuana use. Characteristics of neighborhoods and schools were measured using student, parent, and archival data. The findings of this study show substantial variation across schools in substance use. Contrary to expectations, lifetime alcohol and cigarette use rates were higher in schools located in neighborhoods having greater social advantages as indicated by the perceptions of residents and archival data. [57] Perhaps not surprisingly, a recent study examining factors mediating the effects of parental emotional and instrumental support on adolescents' use of tobacco, alcohol, and marijuana found that parental support was inversely related to substance use. Further analysis of the data from this study indicated that the effect of parental support was mediated through multiple pathways, although in general, the major mediators were higher levels of behavioral coping and academic competence and less tolerance for deviance and behavioral undercontrol. Multiple-group analysis suggested buffering effects occurred because high support reduced the effect of risk factors and increased the effect of protective factors. Results of this study support the position that enhanced coping ability is an important mechanism through which social support contributes to adjustment. [58]

A child's level of cognitive skills may also be a factor in early drug use. A longitudinal study of the relationships between several cognitive skills and drug use over time found a small but significant association between drug use and weak cognitive and affective self-management strategies in early adolescence; this relationship became stronger over time. The exacerbation of these cognitive weaknesses with increased drug use may contribute to impaired social, emotional, and psychological growth in late adolescence. The investigators note that deficits in cognitive efficacy may actually precede and perhaps predispose to problematic drug use. Weaknesses in cognitive skills and learning disabilities may be undetected factors that underlie recognized risk factors such as low self-esteem, academic failure, and school dropout. [59]

Of course, not all children who try drugs continue to use them. To assess risk factors for escalation of substance use once it begins, researchers grouped adolescents according to substance use patterns over three assessments and then examined variables differentiating the groups. The four groups-nonusers, minimal experimenters, late starters, and escalators-were identified through analysis of changes in cigarette, alcohol, and marijuana use among a cohort of eighth and ninth graders enrolled in public schools. By modeling group differences based on variables from stress-coping theory, problem behavior theory, and peer-association theory, the researchers identified measures predictive of subsequent escalation in substance use. Compared with nonusers and minimal experimenters, late starters and escalators had higher life stress, lower parental support, lower academic competence, more deviant attitudes, and more nonadaptive modes of coping; they also were higher in measures of parental and peer substance use. This study also found, in contrast with earlier work, that substance use experimenters, compared with nonusers, had higher stress, more maladaptive coping, more deviance-prone attitudes, lower levels of parental support, and lower levels of self-control. The findings support the idea that some people enter adolescence with less parental support and more life stress, have less adaptive patterns of coping and competence, and tend to gravitate to groups of peer substance users. To the extent that these factors prevail and are not offset, these adolescents become involved in a network of active users. The experience-regulating function of substance use becomes more salient, and they are primed to continue substance use at increasing rates. [60]

The effect of a parent's drug use on the child is well documented. However, a recent study suggests that the sensitive period for the influence of a father's substance use disorder on a son's behavioral problems starts when the son is about 6 years old. These results suggest the importance of early intervention to reduce paternal substance use to prevent intergenerational transmission of behavioral problems and of substance use, given that externalizing behavioral problems in male children and adolescents are among the best predictors of subsequent substance use in early and late adolescence. [61]

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