Ethos Ho, BSc Pharm Candidate
What is an Attention-Deficit Hyperactivity Disorder?
Attention-Deficit Hyperactivity Disorder, also known as ADHD, is the most common psychiatric disorder affecting children between the age of 6 and 17, worldwide.1-3 Although it’s primarily a childhood disorder, about 60 to 80% of the symptoms of ADHD may persist into adulthood.2,3 Thus, ADHD is not just a childhood disorder that resolves during adolescence.3 There is also increasing evidence that late-onset ADHD may occur in young adults with no previous childhood diagnosis.2 ADHD is characterized by chronic, pervasive and disruptive symptoms of inattention and hyperactivity/impulsivity.1-3 While the presence and severity of these symptoms can vary among individuals,2 there are currently three subtypes of ADHD that are recognized:3
- Mostly hyperactive impulsive
- Mostly inattentive
- A combined type
Children and adolescents with ADHD can experience many challenges through their developing years due to impulsive behavior and slower rates of information processing.2,3 In fact, they’re more likely to perform poorly on standardized tests, score lower grades, and drop out of school.3 Furthermore, their impulsiveness has shown to increase their risk of motor vehicle accidents and spontaneous sexual encounters, leading to higher teen pregnancy rates and incidence of sexually transmitted diseases than the general population.3
What Causes ADHD?
The exact cause of ADHD is still unknown and likely involves a complex interplay between genetic and non-genetic factors.4 ADHD was initially believed to be caused by reduced brain function after several observations of reduced brain volume and functionality in those with the disorder.3 This results in deficits in:3
- Cognitive processing
- Motor planning
- Speed of processing responses
- Associated behavioral issues in ADHD
More recent evidence has identified that certain regions of the brain (prefrontal cortex, caudate, and cerebellum) are the primary areas that show deficits in ADHD.3 The networks of activity between these regions are extremely sensitive to certain chemicals, known as neurotransmitters, released in the brain.3 The actions and functions of the neurotransmitters, dopamine and norepinephrine, are now believed to be abnormal in individuals with ADHD.3
Although there is currently no cure for ADHD, drug therapy, behavioral therapy, or a combination of the two is used for symptom management and to improve function.3,4 Today’s article will focus on the pharmacological treatments for ADHD.
Stimulant drugs, which include amphetamines (Ex. Dexedrine®, Vyvanse®, Adderall®) and methylphenidate (Ex. Concerta®, Ritalin®), are approved for use across various age groups for the treatment of ADHD.2,3 The net effect of these drugs is to correct the levels of dopamine and norepinephrine in the brain, reducing the symptoms associated with ADHD and improving functions.3 Although methylphenidate and amphetamines are considered equally effective for the long-term treatment of ADHD, their slight variation in mechanism of action could explain why individuals failing to respond to one stimulant show a better response with the other.3 These drugs are available in extended- and immediate-release forms. While more costly, extended-release formulations offer advantages such as convenience, confidentiality at school/work, and improved compliance.3 Immediate-release forms are recommended for use in children who may be at risk of overdose with long-acting forms.3
Also known as Strattera®, atomoxetine has a similar mechanism of action to stimulants, normalizing the levels of norepinephrine and dopamine in the brain.3 Atomoxetine requires at least 4-6 weeks to show full effect, and may be an option for individuals where substance abuse is a concern.2,3 Atomoxetine may also be used to treat tics and anxiety; therefore, may be useful in individuals who also have these symptoms.2,3
Guanfacine (Intuniv®) and clonidine are medications that act on certain receptors in the brain that help ameliorate the symptoms of ADHD.3 Guanfacine is more selective than clonidine at these receptors and has a longer duration of action and fewer side-effects such as sedation and dizziness.2,3 This makesguanfacine the more advantageous choice. Both Guanfacine and clonidine may be taken alone or combined with stimulants to help treat symptoms of aggression, tics, and insomnia.2,3 Like atomoxetine, the full effect of these medications may take up to 4 weeks.3
Antidepressants that are used to treat ADHD include bupropion (Wellbutrin®), venlafaxine (Effexor®), imipramine, nortriptyline, and desipramine. These agents are less effective than stimulants for the management of symptoms in children; however, they may be beneficial in those who also have depression, anxiety, or tics.2,3 Tricyclic antidepressants such as imipramine, nortriptyline, and desipramine generally aren’t preferred due to their numerous side effects and drug interactions.3 Like the other non-stimulant medications mentioned, antidepressants can take up to 3 to 4 weeks for maximum effect and are better tolerated than stimulants.2,3
The Bottom Line
ADHD is a common psychiatric disorder in children, presenting with symptoms of inattention and hyperactivity/impulsivity that may persist into adulthood. Those with ADHD may experience many challenges academically and socially and are more likely to undertake risky behaviors due to impulsiveness. Although the cause of ADHD is still unknown, it’s likely a complex interplay between genetic and environmental influences. There are emerging studies that point towards an underlying deficiency in brain function, likely caused deficits in certain brain regions that are highly regulated by neurotransmitters such as dopamine and norepinephrine. Treatment options consist of drug therapy, behavioral therapy, or a combination of the two. Drug treatment options include stimulants, which are the most effective long-term treatment of ADHD, and non-stimulants, which take longer to be effective, but do not carry an abuse potential.
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1. Fernández de la Cruz, L., Simonoff, E., McGough, J., Halperin, J., Arnold, L., & Stringaris, A. (2015). Treatment of Children With Attention-Deficit/Hyperactivity Disorder (ADHD) and Irritability: Results From the Multimodal Treatment Study of Children With ADHD (MTA). Journal Of The American Academy Of Child & Adolescent Psychiatry, 54(1), 62-70.e3. doi: 10.1016/j.jaac.2014.10.006
3. Sharma, A., & Couture, J. (2013). A Review of the Pathophysiology, Etiology, and Treatment of Attention-Deficit Hyperactivity Disorder (ADHD). Annals Of Pharmacotherapy, 48(2), 209-225. doi: 10.1177/1060028013510699
4. Tarver, J., Daley, D., & Sayal, K. (2014). Attention-deficit hyperactivity disorder (ADHD): an updated review of the essential facts. Child: Care, Health And Development, 40(6), 762-774. doi: 10.1111/cch.12139