Methadone Maintenance Treatment (MMT) is the most common treatment for women dependent on opioids during pregnancy. A growing body of research suggests that infants and children prenatally exposed to methadone and other opioids are at an increased risk of behavioural and emotional adjustment difficulties. However, the extent to which children prenatally exposed to opioids meet diagnostic criteria for mental health disorders is not known. The current study aimed to compare the early psychiatric outcomes and parent-reported behavioural and emotional adjustment difficulties of methadone-exposed (ME) and non- exposed comparison children at age 4.5 years old. The final aim was to examine the extent to which early-onset psychiatric disorders associated with prenatal opioid exposure might be explained by confounding infant, maternal and socio-familial factors.

The behavioural and emotional adjustment of 87 children born to mothers maintained on methadone during pregnancy and 103 non-exposed comparison children was evaluated in a structured parent interview when the children were 4.5 years old. Caregivers initially completed the Strengths and Difficulties Questionnaire (SDQ) as a screening measure for child behavioural and emotional problems and were then interviewed using the Development and Well-Being Assessment (DAWBA). The DAWBA online scoring system was subsequently used to generate provisional psychiatric disorder diagnoses, which were reviewed alongside other data by a registered clinical psychologist to assign final clinical diagnoses according to DSM-IV criteria. Measures of infant, maternal and socio-familial risk factors were also available from two earlier time points: late pregnancy/birth and at age 18 months.

Caregivers of ME children reported significantly higher levels of conduct problems (p< .0001), hyperactivity/inattention (p < .0001), emotional difficulties (p = .01), peer difficulties (p = .002), total difficulties (p < .0001), and significantly lower levels of prosocial behaviour (p < .0001) on the SDQ compared to caregivers of non-exposed comparison children at age 4.5 years. Caregivers of ME children also reported a significantly higher impact associated with the child’s difficulties (p = .001). With the exception of emotional difficulties (p = .05), a significantly higher proportion of ME children had scores that fell within the clinical range for each of the other SDQ subscales. In terms of externalising disorder diagnoses, ME children had significantly higher rates of any diagnosis of Attention-Deficit Hyperactivity Disorder (ADHD) (p = .001), Conduct Disorder (CD) (p = .003) and Oppositional Defiant Disorder (ODD) (p < .0001). Overall, ME children were not significantly more likely to meet diagnostic criteria for an internalising disorder. Furthermore, ME children were significantly more likely to be diagnosed with comorbid psychiatric disorders (p < .0001). After controlling for confounding variables, group status remained a significant predictor for any diagnosis of ODD/CD at age 4.5 years (p = .02). In contrast, other psychiatric disorder outcomes at age 4.5 years were largely explained by a range of confounding factors which included social risk, maternal psychopathology and poly-drug use.

The findings of the current study suggest that children born to mothers maintained on methadone are at an increased risk of early-onset psychiatric disorder, the most common of which were ADHD, ODD and CD. The risk for externalising disorder was much greater than internalising disorders at age 4.5 years. Findings tend to suggest that a complex interplay of teratogenic, biological and environmental influences may be contributing to ME children’s mental health risk. This raises concerns about the future developmental trajectory of mental health difficulties in ME children and heightens the need for early intervention and ongoing social and clinical support. Future research is necessary to explore the relative contributions of postnatal risk factors that may potentially mediate the relationship between methadone exposure and externalising behaviour disorders in ME children at 4.5 years old.