Biomedical subjects

M T Lynskey

Publications and source records attributed to M T Lynskey.

At least 19 recordsLinked to original sources

PubMed2006

Contrasting models of genetic co-morbidity for cannabis and other illicit drugs in adult Australian twins.

BACKGROUND: The use of cannabis and other illicit drugs (OIDs) and their co-morbid misuse are frequently reported in the literature. Correlated vulnerabilities and causal or gateway influences have been implicated in this association. We investigated the source of this co-morbidity between cannabis use (experimentation, early and repeated use, and problems) and OID experimentation and problems using genetic models proposed by Neale and Kendler (American Journal of Human Genetics 1995, 57, 935-953). METHOD: In a sample of 4152 same-sex male and female adult Australian twin individuals, we fit 13 genetically informative models of co-morbidity to data on experimentation, early use, repeated use of cannabis and co-morbid OID experimentation, and to abuse/dependence (A/D) problems with cannabis and OIDs. RESULTS: Model-fitting results suggest that common genetic, shared and unique environmental factors are responsible for the association between cannabis experimentation, early use, repeated use and A/D problems and OID experimentation or problems. The liability causation model, which is a reduced form of the correlated vulnerabilities model, also fit very well. In women, we found evidence for high-risk cannabis experimenters and repeated users to be at increased risk for OID experimentation, despite being below the risk threshold on the liability distribution for OID experimentation (extreme multiformity). CONCLUSIONS: Co-morbid cannabis and OID use and misuse are due partly to a common predisposition to substance use disorders. Putative causal effects could not be ruled out. These models warrant further research, so that features of the correlated vulnerabilities model and the gateway models can be studied jointly in a single series of adaptive nested models.

Adolescent↗

PubMed2002

Genetic and environmental contributions to cannabis dependence in a national young adult twin sample.

BACKGROUND: This paper examines genetic and environmental contributions to risk of cannabis dependence. METHOD: Symptoms of cannabis dependence and measures of social, family and individual risk factors were assessed in a sample of 6265 young adult male and female Australian twins born 1964-1971. RESULTS: Symptoms of cannabis dependence were common: 11.0% of sample (15.1% of men and 7.8% of women) reported two or more symptoms of dependence. Correlates of cannabis dependence included educational attainment, exposure to parental conflict, sexual abuse, major depression, social anxiety and childhood conduct disorder. However, even after control for the effects of these factors, there was evidence of significant genetic effects on risk of cannabis dependence. Standard genetic modelling indicated that 44.7% (95% CI = 15-72.2) of the variance in liability to cannabis dependence could be accounted for by genetic factors, 20.1% (95% CI = 0-43.6) could be attributed to shared environment factors and 35.3% (95% CI = 26.4-45.7) could be attributed to non-shared environmental factors. However, while there was no evidence of significant gender differences in the magnitude of genetic and environmental influences, a model which assumed both genetic and shared environmental influences on risks of cannabis dependence among men and shared environmental but no genetic influences among women provided an equally good fit to the data. CONCLUSIONS: There was consistent evidence that genetic risk factors are important determinants of risk of cannabis dependence among men. However, it remains uncertain whether there are genetic influences on liability to cannabis dependence among women.

Adult↗

PubMed2002

Patterns of association between alcohol consumption and symptoms of depression and anxiety in young adults.

AIMS: Recent epidemiological findings indicate that non-drinkers as well as hazardous/harmful drinkers experience higher levels of distress than moderate drinkers. Little is known about the age at which this develops. This paper examines levels of affect, depression and anxiety over the full range of alcohol consumption in young adults. DESIGN: Cross-sectional findings from the first wave of a prospective, longitudinal study are presented. PARTICIPANTS: The general population sample comprised of 2404 young adults (aged 20-24 years). living in the Canberra region. Measures included: the Goldberg Depression and Anxiety scales, the Positive and Negative Affect Schedule, and the Alcohol Use Disorders Identification Test. FINDINGS: For men, both non/occasional and hazardous/harmful consumption were associated with lower levels of positive affect and higher levels of anxiety and depression. The higher levels of distress evident for male abstainers were related to being less extroverted and less healthy and not to past hazardous/harmful alcohol consumption, current tobacco or marijuana use. For women, only hazardous/harmful drinkers were found to have higher levels of depression and negative affect. Hazardous/harmful consumption was related to using marijuana, tobacco and recent stressful events in both men and women. CONCLUSIONS: Higher levels of distress are already evident in male non-drinkers in early adulthood. The findings counter theories that distress in non-drinkers is due to past hazardous/harmful alcohol consumption, marijuana or tobacco use, or characteristics in common with hazardous/harmful drinkers. Alcohol use disorders and mental health problems are pertinent issues for young adults. However, more understanding is needed of the experiences of non-drinkers in an alcohol consuming culture.

Adult↗

PubMed2001

Attention deficit hyperactivity disorder and substance use disorders: Is there a causal link?

Attention-deficit hyperactivity disorder (ADHD), characterized by restless, inattentive and hyperactive behaviours, is a relatively common childhood disorder that affects approximately 5% of the general population. There has been controversy about whether ADHD increases risks of developing substance use disorders. The available evidence suggests that, in the absence of conduct disorder, ADHD is not associated with an increased risk of substance use problems in males. There is only limited evidence on the role of ADHD in the aetiology of substance use disorders among females. While ADHD has traditionally been considered as a childhood disorder, it may also occur in adults; research needs to examine the extent to which ADHD in adulthood increases the risk of substance use disorders.

Adolescent↗

PubMed2000

How many dependent heroin users are there in Australia?

OBJECTIVE: To estimate the prevalence of dependent or daily heroin users in Australia, and to compare the prevalence in Australia with that in other developed countries. DESIGN: We applied three different methods of estimation (back-projection, capture-recapture, and multiplier) to data on national opioid overdose deaths in Australia, first-time entrants to methadone maintenance treatment, and heroin-related arrests in New South Wales. We compared our estimates with estimates derived by similar methods in countries of the European Union. DATA SOURCES: Data on national opioid overdose deaths were obtained from the Australian Bureau of Statistics. Data on methadone entrants in NSW were extracted from a database maintained by the NSW Department of Health. Data on arrests for heroin-related offences were supplied by the NSW Police Service. RESULTS: The best estimates of the number of dependent heroin users in Australia in 1997-1998 from the three methods of estimation were between 67 000 and 92 000 and the median estimate was 74 000. The population prevalence was 6.9 per 1000 adults aged 15-54 years. The prevalence of heroin dependence in Australia is the same as that in Britain (7 per 1000) and within the range of recently derived estimates in the European Union (3-8 per 1000 adults aged 15-54 years). CONCLUSIONS: Although the exact figures need to be interpreted with caution, our estimates suggest that Australia has a substantial public health problem with dependent heroin use that is of a magnitude similar to that in comparable European societies.

Adolescent↗

PubMed1999

Opioid overdose mortality in Australia, 1964-1997: birth-cohort trends.

OBJECTIVE: To examine trends in rates of opioid overdose deaths from 1964 to 1997 in different birth cohorts. DESIGN: Age-period-cohort analysis of national data from the Australian Bureau of Statistics. MAIN OUTCOME MEASURES: Annual population rates of death attributed to opioid dependence or accidental opioid poisoning in people aged 15-44 years, by sex and birth cohort (in five-year intervals, 1940-1944 to 1975-1979). RESULTS: The rate of opioid overdose deaths increased 55-fold between 1964 and 1997, from 1.3 to 71.5 per million population aged 15-44 years. The rate of opioid overdose deaths also increased substantially over the eight birth cohorts, with an incidence rate ratio of 20.70 (95% confidence interval, 13.60-31.46) in the 1975-1979 cohort compared with the 1940-1944 cohort. The age at which the cumulative rate of opioid overdose deaths reached 300 per million fell in successive cohorts (for men, from 28 years among those born 1955-1959 to 22 years among those born 1965-1974; for women, from 33 years among those born 1955-1959 to 27 years among those born 1965-1969). CONCLUSIONS: Heroin use in Australia largely began in the early 1970s and rates of heroin use have markedly increased in birth cohorts born since 1950.

Adolescent↗

PubMed1998

The comorbidity of alcohol dependence and affective disorders: treatment implications.

This paper reviews recent literature on the prevalence of alcohol dependence and affective disorders (major depression, dysthymia), the comorbidity of these conditions and the effects of comorbid affective disorders on the outcome of treatment for alcohol dependence. Alcohol dependence and affective disorders co-occur at significantly higher rates than would be expected by chance within the general population. This comorbidity is further elevated in samples of people seeking treatment for alcohol dependence, suggesting that the co-occurrence of affective disorders may be an important determinant of treatment seeking. The results of a number of recent placebo-controlled studies have suggested that pharmacological treatment with anti-depressants may enhance the efficacy of treatment for alcohol dependence in individuals with comorbid affective disorders.

Alcoholism↗

PubMed1998

Cohort trends in age of initiation to heroin use.

This paper examines gender differences and trends over time in the age of initiation to heroin use. Data from two large surveys: the Sydney component of the ANAIDUS, conducted in 1989, and the ASHIDU, conducted in 1994, were used to examine this issue. Together, these studies contained information on 1,292 individuals who identified themselves as heroin users. Results indicated that, while there were no significant gender differences in age of initiation to heroin use, there was a significant (p < 0.001) time trend in the mean age at which heroin was first used. Specifically, the mean age of first heroin use among individuals born during the interval 1940-1949 was 20.5 years while among those born during 1970-1979 the mean age of first heroin use was 16.5 years. These findings were confirmed by analyses of the National Household Survey. Further analysis of the ASHIDU data indicated that younger age of initiation to heroin use was associated with polydrug use, overdose and crime after the effects of duration of heroin use had been statistically controlled. These findings suggest that there has been both an increase in the willingness of young people to experiment with heroin and an increased availability of the drug over this time. In combination with evidence that there has been an increase in the amount of heroin being imported into Australia, and an increased demand for treatment for opiate dependence, these data suggest that Australia is experiencing an increase in the use of heroin, particularly among youth.

Journal Article↗

PubMed1998

The origins of the correlations between tobacco, alcohol, and cannabis use during adolescence.

Methods of structural equation modelling were used to analyse the correlations between reports of tobacco, alcohol, and cannabis use in a birth cohort of New Zealand children studied to the age of 16. This analysis produced three major conclusions: (a) the correlations between tobacco, alcohol, and cannabis use could be explained by a factor representing the individual's vulnerability to substance use; (b) predictors of vulnerability to substance use were the extent to which the individual affiliated with delinquent or substance using peers, novelty seeking, and parental illicit drug use; (c) in the region of 54% of the correlations between substance use behaviours could be predicted from observed risk factors and 46% was attributable to non-observed sources of vulnerability.

Adolescent↗

PubMed1997

Physical punishment/maltreatment during childhood and adjustment in young adulthood.

OBJECTIVE: To study the relationships between retrospective reports of physical punishment/maltreatment and rates of adjustment difficulties at age 18 in a birth cohort of New Zealand subjects. METHOD: Data were gathered over the course of an 18 year longitudinal study of a birth cohort of 1,265 New Zealand born children. At age 18 retrospective reports of exposure to physical punishment/maltreatment were obtained. At this time the cohort was also assessed on measures of psychosocial adjustment juvenile offending, substance abuse behaviors, and psychiatric disorder. RESULTS: Young people reporting exposure to harsh or abusive treatment during childhood had elevated rates of juvenile offending, substance abuse, and mental health problems. However, subsequent analysis using logistic regression methods showed that much of the elevated risk shown by this group was explained by social and contextual factors that were associated with patterns of childhood punishment/maltreatment. Nonetheless, even after control for confounding factors those reporting harsh or abusive childhood experiences were at increased risks of violent offending, suicide attempts, being a victim of violence, and alcohol abuse. CONCLUSION: This study leads to three major conclusions: (1) Those exposed to harsh or abusive treatment during childhood are an at-risk population for juvenile offending, substance abuse, and mental health problems; (2) Much of this elevated risk arises from the social context within which harsh or abusive treatment occurs; (3) Nonetheless, exposure to abuse appears to increase risks of involvement in violent behavior and alcohol abuse.

Adjustment Disorders↗

PubMed1997

Childhood sexual abuse, adolescent sexual behaviors and sexual revictimization.

OBJECTIVE: The aims of this study were to examine the extent to which exposure to childhood sexual abuse (CSA) was associated with increased rates of sexual risk taking behaviors and sexual revictimization during adolescence. METHOD: A birth cohort of 520 New Zealand born young women was studied at regular intervals from birth to the age of 18. At age 18 retrospective reports of CSA were obtained from sample members. Over the course of the 18 year study information was gathered on: (a) childhood, family, and related circumstances; and (b) the young women's history of sexual experiences from 14 to 18 years. RESULTS: Young women reporting CSA, and particularly severe CSA involving intercourse, had significantly higher rates of early onset consensual sexual activity, teenage pregnancy, multiple sexual partners, unprotected intercourse, sexually transmitted disease, and sexual assault after the age of 16. Logistic regression analyses suggested that the associations between CSA and sexual outcomes in adolescence arose by two routes. First, exposure to CSA was associated with a series of childhood and family factors including social disadvantage, family instability, impaired parent child relationships, and parental adjustment difficulties that were also associated with increased sexual vulnerability in adolescence. Second, there appeared to be a causal chain relationship between CSA and sexual experiences in which CSA was associated with early onset sexual activity which, in turn, led to heightened risks of other adverse outcomes in adolescence. CONCLUSIONS: The findings of this study suggest that those exposed to CSA have greater sexual vulnerability during adolescence. This appears to arise because: (a) the childhood and family factors that are associated with CSA are also associated with increased sexual risks during adolescence; and (b) exposure to CSA may encourage early onset sexual activity which places those exposed to CSA at greater sexual risk over the period of adolescence.

Adolescent↗

PubMed1997

Factors protecting against the development of adjustment difficulties in young adults exposed to childhood sexual abuse.

OBJECTIVE: The aims of this study were to identify the factors which discriminated young people exposed to childhood sexual abuse (CSA) who developed psychiatric disorder or adjustment difficulties in young adulthood from those young people exposed to CSA who did not develop psychiatric disorder or adjustment difficulties by age 18. METHOD: Data were gathered on a birth cohort of 1,025 New Zealand children studied from birth to the age of 18 on (a) exposure to CSA; (b) patterns of psychiatric disorder and adjustment difficulties at age 18 years; (c) factors that may have influenced responses to CSA including characteristics of the abuse, parental bonding, parental characteristics, and adolescent peer affiliations. RESULTS: Just over 10% of the cohort reported CSA. Those reporting CSA were at increased risks of a range of difficulties at age 18 (depression, anxiety, conduct disorder, alcohol abuse/dependence, other substance abuse/dependence, post sexual abuse trauma, attempted suicide). However, not all of those exposed to CSA developed difficulties and approximately a quarter of those exposed to CSA did not meet criteria for any adjustment difficulty. Further analysis suggested that the extent of adjustment difficulties in those exposed to CSA was influenced by two additional factors: (a) the extent of affiliations with delinquent or substance using peers in adolescence; and (b) the extent of paternal care or support in childhood. CONCLUSIONS: The findings of this study suggest that while young people exposed to CSA are at increased risks of psychiatric disorder and adjustment difficulties in young adulthood, not all individuals exposed to CSA will develop adjustment difficulties. Important factors protecting against the development of adjustment difficulties in young people experiencing CSA appear to be the nature and quality of peer and family relationships.

Adjustment Disorders↗

PubMed1997

The effects of unemployment on psychiatric illness during young adulthood.

BACKGROUND: The aims of this study were to examine the associations between exposure to unemployment following school leaving and rates of psychiatric disorder using data gathered on a birth cohort of New Zealand young people studied up to the age of 18. METHODS: At age 18 cohort members were assessed on: (a) duration of exposure to unemployment from age 16; (b) DSM-IV diagnostic criteria for major depression, anxiety disorders, conduct disorder, nicotine dependence, other substance abuse/dependence and attempted suicide. This information was integrated into longitudinal data gathered on the social circumstances, family background and adjustment of the cohort up to the age of 18. RESULTS: Increasing exposure to unemployment was associated with increasing risks of psychiatric disorder in adolescence. Those exposed to 6 months or more unemployment had rates of disorder that were 1.5 to 5.4 times higher than those not exposed to unemployment. However, most of the elevated risk of disorder among those unemployed was explained by family and personal factors that were present prior to school leaving age. Nonetheless, even after control for these factors those exposed to unemployment had significantly higher rates of anxiety disorder and substance use disorders. CONCLUSIONS: To a large extent the relationships between unemployment and psychiatric disorder seen in this cohort were explained by social, family and personal factors that were present before school leaving age. Nonetheless, young people exposed to unemployment had higher rates of substance use and anxiety disorder.

Adolescent↗

PubMed1997

Early dentine lead levels and educational outcomes at 18 years.

The associations between early dentine lead levels measured at the age of 6-8 years and educational outcomes measured at 18 years were examined in a birth cohort of 1265 New Zealand children. Analyses showed significant (p < .005) dose/response relationships between early dentine lead levels and later outcomes: at age 18 children with early elevated lead levels had poorer reading abilities, had more often left school early, had more often left school without qualifications, and had lower levels of success in school examinations. These associations persisted after statistical control for a range of social and familial confounding factors. A number of potential threats to the validity of the findings are examined, including sample selection bias, statistical undercontrol of covariates, and errors of measurement. It is concluded that the findings are consistent with the view that early mildly elevated lead levels have modest but detectable effects on individual achievement, with these effects extending to late adolescence.

Achievement↗

PubMed1997

Early reading difficulties and later conduct problems.

The relationships between early reading difficulties and later conduct problems were examined in a birth cohort of New Zealand children studied from the point of school entry to the age of 16. Children with early reading difficulties had increased rates of conduct problems up to the age of 16 years. These associations depended on context, being more evident for boys and tending to reduce with increasing age. However, the associations between early reading difficulties and later conduct problems were explained by the fact that children with early reading difficulties tended to be characterised by a number of disadvantageous features (and notably early-onset conduct problems) that were present before the onset of reading difficulties. When the associations between reading difficulties and conduct problems were adjusted for confounding factors there were no statistically significant associations between reading difficulties and conduct problems. These results were found to hold for various age and gender subgroups of the sample, for measures of reading difficulties defined in different ways, and for a wide range of outcome variables. It is concluded that, when due allowance is made for potentially confounding factors (and notably early conduct problems) and for factors correlated with these problems, it is unlikely that reading difficulties in early childhood are related to later conduct problems.

Adolescent↗

PubMed1997

Attentional difficulties in middle childhood and psychosocial outcomes in young adulthood.

The associations between (dimensionally scored) measures of attentional difficulties at age 8 and psychosocial outcomes at age 18 were examined in a birth cohort of New Zealand children. Increasing attentional difficulties during middle childhood were associated with increased risks of academic failure or difficulties, juvenile offending, and substance use behaviours in young adulthood. However, those with early attentional difficulties were a high-risk group characterised by social disadvantages, early conduct difficulties, lower IQ, and related characteristics. Statistical adjustments showed: (a) that attentional difficulties were related to later academic success even when due allowance was made for potentially confounding factors; and (b) early attentional difficulties were unrelated to later juvenile offending or substance use behaviours after adjustment for confounding. In all cases there was evidence of consistent dose/response relationships between the extent of early attentional difficulties and later academic outcomes, suggesting that these associations were not confined to those with extreme symptoms.

Adolescent↗

PubMed1996

Comorbidity between depressive disorders and nicotine dependence in a cohort of 16-year-olds.

BACKGROUND: There has been growing interest in the associations between cigarette smoking and symptoms of depression. This study documents the comorbidity between depression and nicotine dependence in a birth cohort of 16-year-olds and examines the extent to which comorbidity between depression and nicotine dependence could be explained by risk factors associated with both outcomes. METHODS: Data were gathered during the course of a 16-year longitudinal study of a birth cohort of 947 New Zealand children for (1) depressive disorders and nicotine dependence at age 16 years; and (2) prospectively measured risk factors including family social position, family history of criminality, parental smoking, life events, parental attachment, conduct problems, self-esteem, and affiliations with delinquent peers. RESULTS: There was evidence of moderate to strong comorbidity between depression and nicotine dependence at age 16 years; teenagers with a depressive disorder had odds of nicotine dependence that were 4.6 times those of teenagers without depressive disorder. Analyses using logistic regression and log-linear modeling methods revealed that a substantial component of the comorbidity between depression and nicotine dependence was explained by common or correlated risk factors associated with both outcomes. After adjustment for common or correlated risk factors, the adjusted odds ratio between depression and nicotine dependence was 2.3. CONCLUSIONS: Comorbidities between depression and nicotine dependence seem to be well established by the age of 16 years. Much of this comorbidity can be explained by common or correlated risk factors associated with depression or nicotine dependence.

Adolescent↗

PubMed1996

The short-term consequences of early onset cannabis use.

The associations between early onset (prior to 15 years of age) cannabis use and rates of mental health or adjustment problems during the period from 15 to 16 years of age were studied in a New Zealand birth cohort. Early onset cannabis users were at increased risks of later substance use behaviors, conduct/oppositional disorders, juvenile offending, severe truancy, school dropout, anxiety, depression, and suicidal ideation. Early cannabis users had odds of these outcomes ranging from 2.7 to 30.8 times higher than the odds for those who did not use cannabis prior to age 15. Most of the elevated risks of early onset users were explained by the fact that they were a high-risk groups of adolescents characterized by family disadvantages, early adjustment problems, and high affiliations with substance-using or delinquent peers. Nonetheless, even after adjustment for a wide range of confounding factors, early onset users had increased risks of later cannabis use. It is concluded that while most of the elevated risks of early onset users were explained by social, family, and individual characteristics of this group, early onset users were at increased risks of later cannabis use.

Adolescent↗