Discuss this article at www.facebook.com/CurrentPsychiatry
Does prescribing stimulants to patients with attention-deficit/hyperactivity disorder (ADHD) increase their risk of future substance abuse? Because ADHD is a common pediatric condition with symptoms that often persist into adulthood, and stimulants are an efficacious first-line therapy, this possible association is a concern for psychiatrists whether they treat children or adults.
Some researchers have expressed concerns that stimulant exposure could predispose patients to future substance abuse.1 Proponents of the biologic model of “kindling” hypothesize early exposure to stimulants could increase the risk of later substance use disorders (SUDs) by modifying or “priming” the brain, which then becomes more receptive to illicit drug exposure. Although there is some evidence that stimulant use does increase SUD risk, other evidence suggests stimulant use does not increase susceptibility to SUDs2,3 and some studies have suggested stimulant use in ADHD patients may protect against SUDs.4,5
This article reviews shared characteristics of ADHD and SUDs and the latest research on the association between the clinical use of stimulants and later development of SUDs. We also offer clinical recommendations for assessing and treating ADHD and comorbid SUD.
Compared with those without the disorder, patients with ADHD have a 6.2 times higher risk of developing an SUD.6 Individuals with ADHD experience an earlier age of onset and a longer duration of SUDs.7 Several retrospective and prospective studies reveal ADHD is a risk factor for SUDs.8 A longitudinal study that tracked teenage males with or without ADHD into young adulthood found SUDs were 4 times more common among those with ADHD.9 Up to 45% of adults with ADHD have a history of alcohol abuse or dependence, and up to 30% have a history of illegal drug abuse or dependence.10
Conversely, an estimated 35% to 71% of alcohol abusers and 15% to 25% of substance-dependent patients have ADHD.11 Adults with ADHD and comorbid SUD report earlier onset12 and greater severity13 of substance abuse than adults without ADHD. Patients with ADHD experience earlier onset and higher rates of tobacco smoking by mid-adolescence.14
Developmental psychopathology. Longitudinal studies have suggested certain psychopathologic characteristics of ADHD can predispose an individual to SUDs independent of stimulant exposure. For example, inattention, impulsivity, and hyperactivity predispose an individual to develop an SUD and also are core symptoms of ADHD.15 Another study found impulsivity, impersistence, and difficulty sitting still at age 3 predicted alcohol abuse at age 21.16 A different longitudinal study found novelty-seeking behavior (restlessness, running/jumping and not keeping still, being squirmy and fidgety) between age 6 to 10 predicted adolescent drug abuse and cigarette smoking.17 Poor response inhibition is a key characteristic of ADHD and has been linked to adolescent drinking.18
ADHD may be an independent risk factor for SUD because a common neurobiologic psychopathology may predispose an individual to develop both conditions. The dopamine system has been implicated in SUD, and dysfunction in the dopaminergic circuits—mostly in basal and frontal cortex with consequent defects in executive function and reward system—also has been found in ADHD.19 Cognitive dysfunction associated with ADHD may decrease a patient’s ability to estimate the negative consequences of substance abuse and to delay immediate gratification from drug or alcohol use.
ADHD patients are more vulnerable to SUDs if they have a comorbid condition, such as oppositional defiant disorder,13,20 bipolar disorder,20,21 or conduct disorder (CD).20,22 Patients with ADHD and comorbid CD are estimated to be 8.8 times more likely to have an SUD before age 18 compared with those with ADHD alone.23 Comorbid ADHD and CD may increase patients’ predisposition to develop dependence on highly addictive drugs, such as cocaine or methamphetamine.24 Impaired executive function, behavioral dyscontrol, impulsivity, and peer rejection are common in both ADHD and CD and may increase the risk of developing SUDs in individuals who have both conditions.25 Other risk factors for SUDs in patients with ADHD are listed in Table 1.26
Risk factors for SUDs in patients with ADHD
|Presence of comorbid conditions (ie, oppositional defiant disorder, conduct disorder, bipolar disorder, eating disorder)|
|White or Hispanic race|
|Partially treated or residual ADHD symptoms|
|Attending a competitive college program|
|College youth who had late onset of stimulant treatment|
|Member of a college sorority/fraternity|
|ADHD: attention-deficit/hyperactivity disorder; SUDs: substance use disorders |
Source: Reference 26
Stimulants’ affect on SUD risk
Increased risk. Limited studies suggest exposure to stimulants is a risk factor for developing SUDs. In a longitudinal study, Lambert et al27 followed 218 patients with ADHD and 182 without ADHD into adulthood and found a linear trend between duration of stimulant treatment and prevalence of cocaine dependence. ADHD patients exposed to stimulants for >1 year had the highest prevalence of cocaine abuse (27%), compared with untreated subjects (15%), or those treated with stimulants for <1 year (18%). However, the study did not control for comorbid contributing factors, such as CD.