Cocaine use among young people in Ireland is rising faster than anywhere else in Europe. As the drug becomes more accessible and its harms more visible, understanding who is most at risk is of particular importance. In this study, researchers followed thousands of Irish teens over time to help answer this question.
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Cocaine use is rising around the world. In 2021, more than 22 million people were estimated to have used cocaine. Ireland is at the center of this growing public health challenge. It now ranks among the highest in Europe for cocaine use, particularly among young people aged 15 to 24. Between 2016 and 2022, treatment admissions for cocaine as the primary problem drug increased by nearly 3-fold, overtaking opioids as the leading cause for drug-related treatment in the country. This rise has been accompanied by serious health and social consequences. Cocaine is associated with elevated risks of overdose, heart problems, suicide, and aggression. Hospitalizations and deaths linked to cocaine use have also increased, particularly among young adults in Ireland. These harms extend beyond individuals, affecting families, schools, communities, and healthcare systems, all of which highlight the urgent need for more targeted prevention, early intervention, and recovery strategies. Adolescence and early adulthood are the periods when most substance use begins, making this a critical window for prevention. Yet despite growing concern, there are few recent longitudinal studies, particularly from Ireland or other EU countries, that track risk and protective factors over time.
In this study, researchers aimed to address this gap by using data from Growing Up in Ireland, a large nationally representative study that follows young people over time. Data collected through this study was examined by the research team to better understand how personal, family, and environmental factors are connected to initiating cocaine at ages 17 and 20. Because the study tracked participants across multiple years, it was possible to see how earlier life experiences influenced later behavior, offering insight into when and how risk factors emerge.
Researchers used a longitudinal design, meaning they collected data from the same individuals at 2 time points: once at age 17 and again at age 20. The study included 5,891 participants at age 17 and 4,629 participants at age 20. To focus on new cases of cocaine use, anyone who had already tried cocaine by age 17 was excluded from the age 20 analysis.
The main outcome was whether participants had used cocaine in the past year. Researchers looked at both new cocaine use, meaning those who tried it for the first time during the study, and overall past-year use, which included anyone who had used it recently, regardless of when they first started.
To understand what might influence cocaine use, the study examined a wide range of factors across individual, social, family, and environmental domains. Individual factors included age; gender; early use of substances like alcohol, tobacco, and e-cigarettes; as well as mental health symptoms such as anxiety, depression, and behavioral difficulties. The researchers also assessed childhood reading ability. Family background was another focus. This included parental education, household income, and parental history of substance use problems. Social factors involved peer influences, such as whether friends used cannabis, and the level of school engagement. Environmental factors included characteristics of the neighborhoods where participants lived, such as the availability of youth services and how common drug use was in the area.
To improve the precision of their findings, the researchers used established statistical techniques to address missing data and to consider the fact that participants were drawn from different schools. The goal was to isolate the influence of specific risk factors and make the findings more applicable to young people across Ireland.
In total, the study followed a total of 10,644 participants with an even split between males and females. Most had tried alcohol by age 17, with half having their first drink between ages 15 and 16, and about 1 in 5 starting before age 14. One-third had used e-cigarettes by age 17, 8% had tried tobacco before age 14, and 3% had used other drugs before age 14. About 1/4 showed elevated behavioral or emotional symptoms. Most lived in two-parent households, though 1/3 lived away from parents by age 20. Thirteen percent reported a parental history of substance problems. Over half had friends who used cannabis, 12% lived in neighborhoods where drug use was common, and 1 in 4 reported limited access to youth services. The sample was geographically diverse, with 56% from rural areas and 23% from Dublin. Socioeconomic backgrounds varied, with broad representation across education, income, and occupational classes. Most participants reported liking school, and 1 in 10 attended a disadvantaged school.
Early alcohol use strongly predicts later cocaine risk, especially for males
Overall, cocaine use increased from 4% at age 17 to nearly 23% at age 20. Teens who used alcohol by age 14 had higher odds of using cocaine later. By age 17, their odds were 8 times higher than those who had not started drinking, and by age 20, nearly 20 times higher. Males also had elevated risk, with nearly double the odds of using cocaine at 17 and 1.5 times higher odds by age 20 compared to females. Early e-cigarette use was another strong predictor: at 17, users had 2 times higher odds of trying cocaine, and by 20, their odds remained over 1.5 times higher.
Some mental health problems were associated with increased risk for cocaine use
Mental health and learning ability were also linked to cocaine use later in life. Teens who experienced more emotional “internalizing” symptoms, such as anxiety or sadness, had half the odds of using cocaine by age 20. Similarly, teens with lower childhood reading scores had 1/3 the odds of using cocaine by age 20.
Family configuration and family history of substance use increases teen risk for cocaine use
Family background made a significant difference in early cocaine use. Teens from single-parent households were found to be nearly 3 times more likely to use cocaine by age 17 in the initial analysis. When researchers looked more closely, they found that teens with a parent who had a history of alcohol or drug problems had 2 times greater odds of cocaine use cocaine at age 17.
The strongest social influence was having friends who used cannabis
Social environment played a major role in teen cocaine use. At age 17, teens who had friends who used cannabis had 7 times greater odds of using cocaine. By age 20, the risk was still high – more than 2 times greater odds compared to teens without cannabis-using friends. Teens who said they did not like school were also more likely to use cocaine at age 17, although this connection faded by age 20 and was no longer statistically significant.
Neighborhood and regional factors linked to early cocaine use
Where teens lived also influenced their risk of using cocaine. At age 17, those living in the Dublin region (Ireland’s capital city) had 2 times greater odds of cocaine use compared to teens in other areas. By age 20, they still faced a modestly higher risk. Teens from neighborhoods where drug use was common had more than 2 times the odds of using cocaine at age 17, although this effect was no longer present by age 20.
In this large-scale longitudinal study, the researchers identified several key risk factors that predict cocaine use among Irish adolescents and young adults. The most robust predictor was early substance use, particularly alcohol. Teens who had their first drink by age 14 were nearly 8 times more likely to use cocaine by age 17 and 19 times more likely by age 20, compared to those who started drinking later. This pattern aligns with prior research linking early alcohol and cannabis use with elevated long-term substance risks, although it is unclear from these data whether early alcohol use is a general vulnerability marker for substance use or whether it produces physiologic change that directly increases vulnerability to cocaine exposure. Use of tobacco and e-cigarettes early in life also significantly increased the likelihood of later cocaine use. This supports evidence that nicotine can act as a “gateway drug” and may do so in part by altering brain reward systems in ways that heighten susceptibility to other substances. Clear gender differences were also observed: males had nearly 2 times the odds of females to try cocaine by age 17 and had 1.5 times greater odds by age 20. This echoes previous studies showing that adolescent males tend to engage in earlier and riskier substance use.
Peer influence emerged as one of the most powerful predictors. Teens with cannabis-using friends were over 7 times more likely to try cocaine by age 17 and more than twice as likely by age 20 compared to those without drug-using peers. This reinforces long-standing research showing that peer behavior strongly shapes adolescent substance use norms. While the study did not determine whether peer pressure, access, or self-selection was the primary driver, the association was consistent across both age groups. Moreover, teens who reported disliking school were also more likely to use cocaine at age 17, although this effect disappeared by age 20.
A family history of alcohol or drug problems also increased early cocaine risk. Adolescents with at least one parent with substance use issues were twice as likely to use cocaine at age 17. This supports a wide body of evidence showing that both genetic vulnerability and environmental exposure, including parental modeling and attitudes toward alcohol/drug use, family stress, and impaired attachment, shape substance use risk. By age 20, this association was no longer statistically significant, although the trend persisted.
The study also showed that environmental context mattered. Teens from the Dublin region had significantly higher odds of using cocaine at both ages 17 and 20, while those from neighborhoods where drug use was common had more than double the odds at age 17. These findings are consistent with research showing that neighborhood-level substance use disorder prevalence and drug availability increase adolescent risk for initiation. While neighborhood effects faded by age 20, the regional trend remained, highlighting ongoing concerns about drug access and local markets.
Finally, mental health factors played a nuanced role. Teens with internalizing symptoms, such as anxiety, depression, were less likely to use cocaine by age 20, possibly due to smaller social networks or lower risk-taking tendencies. In contrast, those with externalizing symptoms, such as impulsivity, aggression, were more likely to use by age 17, consistent with research on behavioral disinhibition and substance risk. However, the association between externalizing symptoms and cocaine use did not remain significant in final statistical models, possibly because there are many factors associated with an individual’s mental health symptoms (e.g., substance use, peer substance use, demographic characteristics, etc.) that better accounted for these effects.
This study examined key risk and protective factors associated with first-time cocaine use during late adolescence and early adulthood, using data from a large, nationally representative Irish cohort. The findings revealed that especially early alcohol use, but also early nicotine use, peer cannabis use, family history of substance problems, and living in high-risk environments, significantly increased the likelihood of trying cocaine. In contrast, having internalizing symptoms (anxiety, sadness) were protective against cocaine use.
Brennan, M. M., Cavallaro, M., Mongan, D., Doyle, A., Millar, S. R., Zgaga, L., Smyth, B. P., Nixon, E., Ivers, J. H., Galvin, B., Walsh, C., McCrory, C., & McCarthy, N. D. (2025). Factors associated with cocaine use at 17 and 20 years old: A longitudinal analysis of a nationally representative cohort. Journal of Adolescent Health, 76(3), 488-498. doi: 10.1016/j.jadohealth.2024.10.033.
l
Cocaine use is rising around the world. In 2021, more than 22 million people were estimated to have used cocaine. Ireland is at the center of this growing public health challenge. It now ranks among the highest in Europe for cocaine use, particularly among young people aged 15 to 24. Between 2016 and 2022, treatment admissions for cocaine as the primary problem drug increased by nearly 3-fold, overtaking opioids as the leading cause for drug-related treatment in the country. This rise has been accompanied by serious health and social consequences. Cocaine is associated with elevated risks of overdose, heart problems, suicide, and aggression. Hospitalizations and deaths linked to cocaine use have also increased, particularly among young adults in Ireland. These harms extend beyond individuals, affecting families, schools, communities, and healthcare systems, all of which highlight the urgent need for more targeted prevention, early intervention, and recovery strategies. Adolescence and early adulthood are the periods when most substance use begins, making this a critical window for prevention. Yet despite growing concern, there are few recent longitudinal studies, particularly from Ireland or other EU countries, that track risk and protective factors over time.
In this study, researchers aimed to address this gap by using data from Growing Up in Ireland, a large nationally representative study that follows young people over time. Data collected through this study was examined by the research team to better understand how personal, family, and environmental factors are connected to initiating cocaine at ages 17 and 20. Because the study tracked participants across multiple years, it was possible to see how earlier life experiences influenced later behavior, offering insight into when and how risk factors emerge.
Researchers used a longitudinal design, meaning they collected data from the same individuals at 2 time points: once at age 17 and again at age 20. The study included 5,891 participants at age 17 and 4,629 participants at age 20. To focus on new cases of cocaine use, anyone who had already tried cocaine by age 17 was excluded from the age 20 analysis.
The main outcome was whether participants had used cocaine in the past year. Researchers looked at both new cocaine use, meaning those who tried it for the first time during the study, and overall past-year use, which included anyone who had used it recently, regardless of when they first started.
To understand what might influence cocaine use, the study examined a wide range of factors across individual, social, family, and environmental domains. Individual factors included age; gender; early use of substances like alcohol, tobacco, and e-cigarettes; as well as mental health symptoms such as anxiety, depression, and behavioral difficulties. The researchers also assessed childhood reading ability. Family background was another focus. This included parental education, household income, and parental history of substance use problems. Social factors involved peer influences, such as whether friends used cannabis, and the level of school engagement. Environmental factors included characteristics of the neighborhoods where participants lived, such as the availability of youth services and how common drug use was in the area.
To improve the precision of their findings, the researchers used established statistical techniques to address missing data and to consider the fact that participants were drawn from different schools. The goal was to isolate the influence of specific risk factors and make the findings more applicable to young people across Ireland.
In total, the study followed a total of 10,644 participants with an even split between males and females. Most had tried alcohol by age 17, with half having their first drink between ages 15 and 16, and about 1 in 5 starting before age 14. One-third had used e-cigarettes by age 17, 8% had tried tobacco before age 14, and 3% had used other drugs before age 14. About 1/4 showed elevated behavioral or emotional symptoms. Most lived in two-parent households, though 1/3 lived away from parents by age 20. Thirteen percent reported a parental history of substance problems. Over half had friends who used cannabis, 12% lived in neighborhoods where drug use was common, and 1 in 4 reported limited access to youth services. The sample was geographically diverse, with 56% from rural areas and 23% from Dublin. Socioeconomic backgrounds varied, with broad representation across education, income, and occupational classes. Most participants reported liking school, and 1 in 10 attended a disadvantaged school.
Early alcohol use strongly predicts later cocaine risk, especially for males
Overall, cocaine use increased from 4% at age 17 to nearly 23% at age 20. Teens who used alcohol by age 14 had higher odds of using cocaine later. By age 17, their odds were 8 times higher than those who had not started drinking, and by age 20, nearly 20 times higher. Males also had elevated risk, with nearly double the odds of using cocaine at 17 and 1.5 times higher odds by age 20 compared to females. Early e-cigarette use was another strong predictor: at 17, users had 2 times higher odds of trying cocaine, and by 20, their odds remained over 1.5 times higher.
Some mental health problems were associated with increased risk for cocaine use
Mental health and learning ability were also linked to cocaine use later in life. Teens who experienced more emotional “internalizing” symptoms, such as anxiety or sadness, had half the odds of using cocaine by age 20. Similarly, teens with lower childhood reading scores had 1/3 the odds of using cocaine by age 20.
Family configuration and family history of substance use increases teen risk for cocaine use
Family background made a significant difference in early cocaine use. Teens from single-parent households were found to be nearly 3 times more likely to use cocaine by age 17 in the initial analysis. When researchers looked more closely, they found that teens with a parent who had a history of alcohol or drug problems had 2 times greater odds of cocaine use cocaine at age 17.
The strongest social influence was having friends who used cannabis
Social environment played a major role in teen cocaine use. At age 17, teens who had friends who used cannabis had 7 times greater odds of using cocaine. By age 20, the risk was still high – more than 2 times greater odds compared to teens without cannabis-using friends. Teens who said they did not like school were also more likely to use cocaine at age 17, although this connection faded by age 20 and was no longer statistically significant.
Neighborhood and regional factors linked to early cocaine use
Where teens lived also influenced their risk of using cocaine. At age 17, those living in the Dublin region (Ireland’s capital city) had 2 times greater odds of cocaine use compared to teens in other areas. By age 20, they still faced a modestly higher risk. Teens from neighborhoods where drug use was common had more than 2 times the odds of using cocaine at age 17, although this effect was no longer present by age 20.
In this large-scale longitudinal study, the researchers identified several key risk factors that predict cocaine use among Irish adolescents and young adults. The most robust predictor was early substance use, particularly alcohol. Teens who had their first drink by age 14 were nearly 8 times more likely to use cocaine by age 17 and 19 times more likely by age 20, compared to those who started drinking later. This pattern aligns with prior research linking early alcohol and cannabis use with elevated long-term substance risks, although it is unclear from these data whether early alcohol use is a general vulnerability marker for substance use or whether it produces physiologic change that directly increases vulnerability to cocaine exposure. Use of tobacco and e-cigarettes early in life also significantly increased the likelihood of later cocaine use. This supports evidence that nicotine can act as a “gateway drug” and may do so in part by altering brain reward systems in ways that heighten susceptibility to other substances. Clear gender differences were also observed: males had nearly 2 times the odds of females to try cocaine by age 17 and had 1.5 times greater odds by age 20. This echoes previous studies showing that adolescent males tend to engage in earlier and riskier substance use.
Peer influence emerged as one of the most powerful predictors. Teens with cannabis-using friends were over 7 times more likely to try cocaine by age 17 and more than twice as likely by age 20 compared to those without drug-using peers. This reinforces long-standing research showing that peer behavior strongly shapes adolescent substance use norms. While the study did not determine whether peer pressure, access, or self-selection was the primary driver, the association was consistent across both age groups. Moreover, teens who reported disliking school were also more likely to use cocaine at age 17, although this effect disappeared by age 20.
A family history of alcohol or drug problems also increased early cocaine risk. Adolescents with at least one parent with substance use issues were twice as likely to use cocaine at age 17. This supports a wide body of evidence showing that both genetic vulnerability and environmental exposure, including parental modeling and attitudes toward alcohol/drug use, family stress, and impaired attachment, shape substance use risk. By age 20, this association was no longer statistically significant, although the trend persisted.
The study also showed that environmental context mattered. Teens from the Dublin region had significantly higher odds of using cocaine at both ages 17 and 20, while those from neighborhoods where drug use was common had more than double the odds at age 17. These findings are consistent with research showing that neighborhood-level substance use disorder prevalence and drug availability increase adolescent risk for initiation. While neighborhood effects faded by age 20, the regional trend remained, highlighting ongoing concerns about drug access and local markets.
Finally, mental health factors played a nuanced role. Teens with internalizing symptoms, such as anxiety, depression, were less likely to use cocaine by age 20, possibly due to smaller social networks or lower risk-taking tendencies. In contrast, those with externalizing symptoms, such as impulsivity, aggression, were more likely to use by age 17, consistent with research on behavioral disinhibition and substance risk. However, the association between externalizing symptoms and cocaine use did not remain significant in final statistical models, possibly because there are many factors associated with an individual’s mental health symptoms (e.g., substance use, peer substance use, demographic characteristics, etc.) that better accounted for these effects.
This study examined key risk and protective factors associated with first-time cocaine use during late adolescence and early adulthood, using data from a large, nationally representative Irish cohort. The findings revealed that especially early alcohol use, but also early nicotine use, peer cannabis use, family history of substance problems, and living in high-risk environments, significantly increased the likelihood of trying cocaine. In contrast, having internalizing symptoms (anxiety, sadness) were protective against cocaine use.
Brennan, M. M., Cavallaro, M., Mongan, D., Doyle, A., Millar, S. R., Zgaga, L., Smyth, B. P., Nixon, E., Ivers, J. H., Galvin, B., Walsh, C., McCrory, C., & McCarthy, N. D. (2025). Factors associated with cocaine use at 17 and 20 years old: A longitudinal analysis of a nationally representative cohort. Journal of Adolescent Health, 76(3), 488-498. doi: 10.1016/j.jadohealth.2024.10.033.
l
Cocaine use is rising around the world. In 2021, more than 22 million people were estimated to have used cocaine. Ireland is at the center of this growing public health challenge. It now ranks among the highest in Europe for cocaine use, particularly among young people aged 15 to 24. Between 2016 and 2022, treatment admissions for cocaine as the primary problem drug increased by nearly 3-fold, overtaking opioids as the leading cause for drug-related treatment in the country. This rise has been accompanied by serious health and social consequences. Cocaine is associated with elevated risks of overdose, heart problems, suicide, and aggression. Hospitalizations and deaths linked to cocaine use have also increased, particularly among young adults in Ireland. These harms extend beyond individuals, affecting families, schools, communities, and healthcare systems, all of which highlight the urgent need for more targeted prevention, early intervention, and recovery strategies. Adolescence and early adulthood are the periods when most substance use begins, making this a critical window for prevention. Yet despite growing concern, there are few recent longitudinal studies, particularly from Ireland or other EU countries, that track risk and protective factors over time.
In this study, researchers aimed to address this gap by using data from Growing Up in Ireland, a large nationally representative study that follows young people over time. Data collected through this study was examined by the research team to better understand how personal, family, and environmental factors are connected to initiating cocaine at ages 17 and 20. Because the study tracked participants across multiple years, it was possible to see how earlier life experiences influenced later behavior, offering insight into when and how risk factors emerge.
Researchers used a longitudinal design, meaning they collected data from the same individuals at 2 time points: once at age 17 and again at age 20. The study included 5,891 participants at age 17 and 4,629 participants at age 20. To focus on new cases of cocaine use, anyone who had already tried cocaine by age 17 was excluded from the age 20 analysis.
The main outcome was whether participants had used cocaine in the past year. Researchers looked at both new cocaine use, meaning those who tried it for the first time during the study, and overall past-year use, which included anyone who had used it recently, regardless of when they first started.
To understand what might influence cocaine use, the study examined a wide range of factors across individual, social, family, and environmental domains. Individual factors included age; gender; early use of substances like alcohol, tobacco, and e-cigarettes; as well as mental health symptoms such as anxiety, depression, and behavioral difficulties. The researchers also assessed childhood reading ability. Family background was another focus. This included parental education, household income, and parental history of substance use problems. Social factors involved peer influences, such as whether friends used cannabis, and the level of school engagement. Environmental factors included characteristics of the neighborhoods where participants lived, such as the availability of youth services and how common drug use was in the area.
To improve the precision of their findings, the researchers used established statistical techniques to address missing data and to consider the fact that participants were drawn from different schools. The goal was to isolate the influence of specific risk factors and make the findings more applicable to young people across Ireland.
In total, the study followed a total of 10,644 participants with an even split between males and females. Most had tried alcohol by age 17, with half having their first drink between ages 15 and 16, and about 1 in 5 starting before age 14. One-third had used e-cigarettes by age 17, 8% had tried tobacco before age 14, and 3% had used other drugs before age 14. About 1/4 showed elevated behavioral or emotional symptoms. Most lived in two-parent households, though 1/3 lived away from parents by age 20. Thirteen percent reported a parental history of substance problems. Over half had friends who used cannabis, 12% lived in neighborhoods where drug use was common, and 1 in 4 reported limited access to youth services. The sample was geographically diverse, with 56% from rural areas and 23% from Dublin. Socioeconomic backgrounds varied, with broad representation across education, income, and occupational classes. Most participants reported liking school, and 1 in 10 attended a disadvantaged school.
Early alcohol use strongly predicts later cocaine risk, especially for males
Overall, cocaine use increased from 4% at age 17 to nearly 23% at age 20. Teens who used alcohol by age 14 had higher odds of using cocaine later. By age 17, their odds were 8 times higher than those who had not started drinking, and by age 20, nearly 20 times higher. Males also had elevated risk, with nearly double the odds of using cocaine at 17 and 1.5 times higher odds by age 20 compared to females. Early e-cigarette use was another strong predictor: at 17, users had 2 times higher odds of trying cocaine, and by 20, their odds remained over 1.5 times higher.
Some mental health problems were associated with increased risk for cocaine use
Mental health and learning ability were also linked to cocaine use later in life. Teens who experienced more emotional “internalizing” symptoms, such as anxiety or sadness, had half the odds of using cocaine by age 20. Similarly, teens with lower childhood reading scores had 1/3 the odds of using cocaine by age 20.
Family configuration and family history of substance use increases teen risk for cocaine use
Family background made a significant difference in early cocaine use. Teens from single-parent households were found to be nearly 3 times more likely to use cocaine by age 17 in the initial analysis. When researchers looked more closely, they found that teens with a parent who had a history of alcohol or drug problems had 2 times greater odds of cocaine use cocaine at age 17.
The strongest social influence was having friends who used cannabis
Social environment played a major role in teen cocaine use. At age 17, teens who had friends who used cannabis had 7 times greater odds of using cocaine. By age 20, the risk was still high – more than 2 times greater odds compared to teens without cannabis-using friends. Teens who said they did not like school were also more likely to use cocaine at age 17, although this connection faded by age 20 and was no longer statistically significant.
Neighborhood and regional factors linked to early cocaine use
Where teens lived also influenced their risk of using cocaine. At age 17, those living in the Dublin region (Ireland’s capital city) had 2 times greater odds of cocaine use compared to teens in other areas. By age 20, they still faced a modestly higher risk. Teens from neighborhoods where drug use was common had more than 2 times the odds of using cocaine at age 17, although this effect was no longer present by age 20.
In this large-scale longitudinal study, the researchers identified several key risk factors that predict cocaine use among Irish adolescents and young adults. The most robust predictor was early substance use, particularly alcohol. Teens who had their first drink by age 14 were nearly 8 times more likely to use cocaine by age 17 and 19 times more likely by age 20, compared to those who started drinking later. This pattern aligns with prior research linking early alcohol and cannabis use with elevated long-term substance risks, although it is unclear from these data whether early alcohol use is a general vulnerability marker for substance use or whether it produces physiologic change that directly increases vulnerability to cocaine exposure. Use of tobacco and e-cigarettes early in life also significantly increased the likelihood of later cocaine use. This supports evidence that nicotine can act as a “gateway drug” and may do so in part by altering brain reward systems in ways that heighten susceptibility to other substances. Clear gender differences were also observed: males had nearly 2 times the odds of females to try cocaine by age 17 and had 1.5 times greater odds by age 20. This echoes previous studies showing that adolescent males tend to engage in earlier and riskier substance use.
Peer influence emerged as one of the most powerful predictors. Teens with cannabis-using friends were over 7 times more likely to try cocaine by age 17 and more than twice as likely by age 20 compared to those without drug-using peers. This reinforces long-standing research showing that peer behavior strongly shapes adolescent substance use norms. While the study did not determine whether peer pressure, access, or self-selection was the primary driver, the association was consistent across both age groups. Moreover, teens who reported disliking school were also more likely to use cocaine at age 17, although this effect disappeared by age 20.
A family history of alcohol or drug problems also increased early cocaine risk. Adolescents with at least one parent with substance use issues were twice as likely to use cocaine at age 17. This supports a wide body of evidence showing that both genetic vulnerability and environmental exposure, including parental modeling and attitudes toward alcohol/drug use, family stress, and impaired attachment, shape substance use risk. By age 20, this association was no longer statistically significant, although the trend persisted.
The study also showed that environmental context mattered. Teens from the Dublin region had significantly higher odds of using cocaine at both ages 17 and 20, while those from neighborhoods where drug use was common had more than double the odds at age 17. These findings are consistent with research showing that neighborhood-level substance use disorder prevalence and drug availability increase adolescent risk for initiation. While neighborhood effects faded by age 20, the regional trend remained, highlighting ongoing concerns about drug access and local markets.
Finally, mental health factors played a nuanced role. Teens with internalizing symptoms, such as anxiety, depression, were less likely to use cocaine by age 20, possibly due to smaller social networks or lower risk-taking tendencies. In contrast, those with externalizing symptoms, such as impulsivity, aggression, were more likely to use by age 17, consistent with research on behavioral disinhibition and substance risk. However, the association between externalizing symptoms and cocaine use did not remain significant in final statistical models, possibly because there are many factors associated with an individual’s mental health symptoms (e.g., substance use, peer substance use, demographic characteristics, etc.) that better accounted for these effects.
This study examined key risk and protective factors associated with first-time cocaine use during late adolescence and early adulthood, using data from a large, nationally representative Irish cohort. The findings revealed that especially early alcohol use, but also early nicotine use, peer cannabis use, family history of substance problems, and living in high-risk environments, significantly increased the likelihood of trying cocaine. In contrast, having internalizing symptoms (anxiety, sadness) were protective against cocaine use.
Brennan, M. M., Cavallaro, M., Mongan, D., Doyle, A., Millar, S. R., Zgaga, L., Smyth, B. P., Nixon, E., Ivers, J. H., Galvin, B., Walsh, C., McCrory, C., & McCarthy, N. D. (2025). Factors associated with cocaine use at 17 and 20 years old: A longitudinal analysis of a nationally representative cohort. Journal of Adolescent Health, 76(3), 488-498. doi: 10.1016/j.jadohealth.2024.10.033.
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