Does substance use affect educational outcomes?

Government policies and alcohol use

As noted, natural experiments are often based on a policy that changes the incentives facing a subpopulation. An obvious example would be a state excise tax on alcoholic beverages. A number of studies using data from the US have examined the relationship between beer taxes and youth drinking. Their results have been decidedly mixed.

In contrast, the evidence for the relationship between the minimum legal drinking age and alcohol consumption is much stronger. A number of studies have found that increasing the minimum legal drinking age from 18 to 21 discourages drinking. In addition, there is evidence that alcohol consumption increases sharply at the minimum legal drinking age.

Alcohol use and academic performance

The sharp increase in alcohol consumption at the minimum legal drinking age has been exploited by researchers who are interested in the determinants of academic performance as measured by grades. For instance, a 2011 study based on data from the United States Air Force Academy found that gaining legal access to alcohol at age 21, the minimum legal drinking age, leads to a reduction in test scores of one-tenth of a standard deviation [1]. Although this reduction was precisely estimated, it may not reflect what happens when the typical university student gains legal access to alcohol. The Air Force Academy is extremely selective, most of its students are male, and most go on to become commissioned officers in the United States Air Force. Furthermore, underage drinking is strictly prohibited at the Academy, a policy that could discourage high school students who are disposed to drinking from applying.

A recent study based on data from the University of Oregon used a similar empirical strategy to estimate the relationship between alcohol consumption and academic performance [2]. Students at the University of Oregon can be thought of as representative of students at public four-year institutions in the US. Academic performance fell when students turned 21 before the end of an academic term (see Figure 1). Specifically, turning 21 is associated with a 0.03 decrease in grade point average (or GPA)—relative to a mean GPA of 3.11 among students in the sample. Moreover, using data on US students from the 1997 National Longitudinal Survey of Youth, this study found that turning 21 was associated with a substantial increase in alcohol consumption. Specifically, the mean number of days per month on which alcohol was consumed increased from 4.3 to 5.7, a rise of almost one-third.

Taken together, the estimates discussed above suggest that reaching the legal drinking age leads to a modest reduction in the academic performance of university students. However, if one is interested in whether alcohol consumption affects academic performance outside the university setting, these studies are of limited value, because most 21-year-olds have either dropped out or graduated from high school. Moreover, due to data limitations, these studies could not pin down the mechanisms through which drinking reduces the academic performance of university students. It could be that drinking takes time away from studying. Drinking could also make it more difficult to concentrate in the classroom or lead to unexcused absences from school.

Evidence on the mechanisms through which drinking reduces academic performance comes from the National Longitudinal Study of Adolescent Health, a survey of US middle school and high school students begun in the mid-1990s. The survey asks respondents about binge drinking, defined as having five or more drinks in a row at one sitting (the standard definition used by medical researchers). Respondents still in middle school who go from not drinking to binge drinking at least twice a month experience a 0.14–0.17 reduction in GPA and are more likely to have unexcused absences [3]. There is also evidence that survey respondents who drink to excess were more likely to report having trouble at school (defined as having difficulty paying attention, completing homework, or getting along with teachers).

Alcohol use and educational attainment

Although drinking appears to reduce academic performance among university students, albeit modestly, there is little evidence that it reduces educational attainment.

An often-cited US study examines what happened to drinking habits and several measures of educational attainment when states increased the minimum legal drinking age from 18 to 21 [4]. It found that restricting access to alcohol in this fashion led to sharp reductions in drinking participation, moderate drinking, and heavy drinking.

However, the study found no evidence that raising the minimum legal drinking age from 18 to 21 had an effect on educational attainment. In fact, estimates of the effects of raising the minimum legal drinking age on educational attainment, although imprecise (statistically insignificant), were often negative. For instance, increasing the minimum legal drinking age from 18 to 21 was associated with a lower probability of entering university and a lower probability of graduating from university. The estimated relationship between increasing the minimum legal drinking age and completing high school was positive, but statistically indistinguishable from zero.

Government policies and the use of illegal drugs

There is evidence from cross-sectional data of a negative association between the price of marijuana and maximum fines for its possession [5]. There is also evidence that the price of marijuana is lower in states without conditional discharge provisions (conditional discharge allows first-time offenders to have their record expunged after serving probation) [5].

Although these associations are consistent with the hypothesis that demand is sensitive to policies intended to discourage drug use, they could easily reflect difficult-to-observe factors at the state level. Because there is very little within-state variation over time in fines and other sanctions, their effects are difficult to distinguish from the effects of other policies and policing effort.

Countries such as Argentina, Colombia, Italy, Spain, and Switzerland have recently removed criminal sanctions for the use and possession of small amounts of marijuana. Decriminalization offers researchers an excellent opportunity to examine illicit drug use before and after a dramatic, well-publicized change in policy.

Some policymakers have argued that decriminalization leads to increased marijuana use [6]. However, empirical support for this argument is lacking. For instance, marijuana use among Dutch teenagers and young adults did not increase after the Netherlands decriminalized marijuana in 1976 [7]. However, “coffee-shop” commercialization, which took place after 1983, might have contributed to an increase in marijuana use among Dutch teenagers and young adults [7].

Portugal decriminalized the use and possession of all illicit drugs (including cocaine, ecstasy, heroin, marijuana, and methamphetamine) on July 1, 2001. Although the use of illicit drugs in Portugal increased after 2001, comparable increases took place in Italy and Spain, where these drugs had not been decriminalized [6]. Illicit drug use among 15- and 16-year-olds in Portugal appears to have increased immediately after decriminalization both in absolute terms and as compared with other countries in the European Union, but then fell from 2003 through 2007 [6].

To date, 23 states in the US and several countries (including Austria, the Czech Republic, and Israel) have legalized the use of marijuana for medical purposes (see Medical marijuana laws). The legalization of medical marijuana represents another policy change that could potentially be exploited by researchers for producing causal estimates, but there is little evidence that teenagers actually respond when these changes occur.

An unpublished, and controversial, study examined the effect of legalizing the medical use of marijuana on US students enrolled in high school [8]. There appears to have been a slight fall in marijuana use immediately after the legalization of medical marijuana (labeled “Year of law change” in Figure 2), followed by an increase of comparable magnitude. Although the trends shown in Figure 2 are unadjusted, they suggest that legalizing medical marijuana does not lead to an abrupt or particularly large change in behavior. Since the mid-2000s, marijuana use among US high school students has increased approximately 4 percentage points. Figure 2 provides little evidence that this increase is the result of legalizing marijuana for medical purposes. (Figure 3 provides details of when medical marijuana was legalized in different states.)

Finally, government-sponsored anti-drug programs, such as the Montana Meth Project and Project DARE (Drug Abuse Resistance Education) in the US, are often claimed by advocates to reduce the demand for illicit drugs. However, careful empirical studies suggest otherwise. The Montana Meth Project was an advertising campaign that featured billboards and television ads with extremely graphic images. After its introduction, methamphetamine use among high school students in Montana declined, but comparable declines occurred in neighboring states over the same time period [9]. More than a dozen studies have examined the impact of Project DARE, a school-based program focused on building self-esteem and teaching students to resist peer pressure, the annual cost of which is estimated to lie between $200 million and $1 billion [10]. Meta-analyses based on the results of the studies have concluded that Project DARE does not appreciably reduce substance use. The DARE curriculum was revised in 2003, but the revision does not appear to have increased its effectiveness [11].

Illicit drugs, academic performance, and educational attainment

Students who use illicit drugs tend to perform poorly in school. This is the case whether the student is using marijuana or harder drugs such as cocaine [12]. Moreover, the use of illicit drugs is negatively associated with educational attainment. Of 18- through 20-year-olds in the US who reported using an illicit drug in the previous month, the percentage was higher among students who had dropped out of school before graduating from high school than among those who graduated or were still in school (see Illustration). Approximately 27% of dropouts had used an illicit drug in the previous month, compared with 22% of those who had graduated or were still in school. The negative association between illicit drug use and educational attainment is generally robust to controlling for observable characteristics such as ethnicity, family income, gender, parental education, race, and urban status.

One recent study showed that high school students in South Dakota who used marijuana were more likely to drop out of school than their counterparts who did not use marijuana [13]. However, much of this association could be explained by attitudes and behaviors measured at grade 7. The remainder was explained by concurrent cigarette use. Because there is no reason to believe that smoking should affect cognition, the authors attributed the association between marijuana use and dropping out of high school to difficult-to-observe factors at the individual level [13].

Because teenagers and young adults do not seem particularly responsive to changes in drug policies, at least in the short term, it is exceedingly difficult to assess whether illicit drug use does in fact affect education outcomes or whether the associations are instead spurious and attributable to individual characteristics such as personality or preferences.