The links between ADHD and addictive disorders have been the subject of a large number of studies showing a high prevalence rate of ADHD in substance abusing populations as well as an increased risk of substance use disorder (SUD) in ADHD patients that may be independent of other psychiatric conditions. High prevalence of ADHD has also been highlighted among individuals suffering from other addictive disorders such as pathological gambling. Adequate diagnosis of ADHD in SUD patients is challenged by phenomenological aspects of addiction and by frequently associated other psychiatric disorders that overlap with key symptoms of ADHD. A detailed comprehensive search for child and adult symptoms including the temporal relationship of ADHD, substance use and other psychiatric disorders should maximize the validity and the reliability of adult ADHD diagnosis in this population. Further, a follow-up evaluation of ADHD symptoms during treatment of SUD may reduce the likelihood of misdiagnosis. Finally, it should be noticed that when SUD occurs with ADHD, it is associated with a greater severity of SUD compared to other SUD patients. This has been shown with an earlier age at onset, antisocial behavior, risk for depression, chronicity of substance use, need for hospitalization and likelihood of a complicated course. Recent data suggest that the effects of ADHD on SUD outcomes are independent of other psychiatric comorbidities. This highlights the need of an earlier implementation of preventive interventions for substance use or behavioral addiction in children/adolescents with ADHD and the necessity to consider this disorder in the treatment of addictive disorders. Benefices and risk of MPH in adult patients with addiction and ADHD are discussed.

The prevalence of adult ADHD is estimated to 5.3% and is often comorbid with substance use disorder (SUD) . The odds Ratio ranges from 1.5 to 7.9, depending on the substance and the dependence level. Conversely, the prevalence of ADHD among patients with SUD is 10.8%, versus 3.8% for patients without SUD. Methylphenidate (MPH) alleviates ADHD symptoms and is currently considered as a first choice medication. MPH competitively binds and blocks the dopamine (DAT) and norepinephrine (NET) transporters with no or low affinity for the serotonin transporter . This mechanism of action is similar to a cocaine intake, which results in a rapid increase of the synaptic dopamine concentration preferentially in the nucleus accumbens . However, the subjective effects are highly dependent on the rate of input. Oral or IV MPH leads to different effects even when the increase of dopamine concentration is comparable. It is more the change per unit time of the dopamine increase (rapid elevation) that is associated to the perception of euphoria than the increase of dopamine itself . A formulation with a slow rate of delivery will lead to a lower risk of reinforcing effect (euphoria) and abuse than an immediate release formulation. The benefits of MPH in adult ADHD have been demonstrated in open-label prospective studies and in randomized clinical trials. Meanwhile prescribing MPH to patients with comorbid SUD has always been challenging for clinicians. In this presentation, we will address the benefits and pitfalls of using MPH in adults with ADHD comorbid SUD, depending on the type of SUD: amphetamine, cocaine, nicotine, alcohol, cannabis and opiates. Overall, due to the prevalence of ADHD in SUD and to the benefits of MPH observed in this population, and considering the mild or low side effects observed, the response to MPH treatment deserve to be evaluated individually.