From the Guidelines
The biochemical explanation for ADHD primarily involves dysregulation of neurotransmitters in the brain, particularly dopamine and norepinephrine, which play crucial roles in attention, focus, impulse control, and executive functioning. In individuals with ADHD, there appears to be insufficient dopamine and norepinephrine activity in specific brain regions, especially the prefrontal cortex which controls executive functions. This deficiency may result from several factors: faster reuptake of these neurotransmitters (meaning they're removed from the synapse too quickly), reduced receptor sensitivity, or decreased neurotransmitter production 1.
Key Factors in ADHD Biochemistry
- Dysregulation of dopamine and norepinephrine
- Insufficient activity in specific brain regions, especially the prefrontal cortex
- Faster reuptake, reduced receptor sensitivity, or decreased neurotransmitter production as potential causes
Medications for ADHD, such as stimulants like methylphenidate (Ritalin, Concerta) and amphetamine-based medications (Adderall, Vyvanse), work by increasing dopamine and norepinephrine levels in the brain 1. Non-stimulant medications like atomoxetine (Strattera) specifically target norepinephrine reuptake. Genetic factors play a significant role in this biochemical imbalance, with ADHD showing high heritability 1. Research also indicates structural differences in the brains of people with ADHD, including variations in the size and activity of certain brain regions involved in attention and impulse control, which further contribute to the neurochemical imbalances observed.
Treatment Implications
- Stimulants increase dopamine and norepinephrine levels
- Non-stimulant medications target norepinephrine reuptake
- Genetic factors and structural brain differences contribute to biochemical imbalances in ADHD
From the FDA Drug Label
The precise mechanism by which atomoxetine produces its therapeutic effects in Attention-Deficit/Hyperactivity Disorder (ADHD) is unknown, but is thought to be related to selective inhibition of the pre-synaptic norepinephrine transporter, as determined in ex vivo uptake and neurotransmitter depletion studies.
The biochemical explanation for ADHD is unknown, but it is thought to be related to the selective inhibition of the pre-synaptic norepinephrine transporter. This suggests that ADHD may be associated with an imbalance of norepinephrine in the brain, and that atomoxetine may help to regulate this imbalance by inhibiting the reuptake of norepinephrine. However, the exact mechanism is not fully understood 2.
- Key points:
- The biochemical explanation for ADHD is unknown
- Atomoxetine may help to regulate the imbalance of norepinephrine in the brain
- The exact mechanism of atomoxetine is not fully understood
- Norepinephrine is thought to play a role in the therapeutic effects of atomoxetine in ADHD.
From the Research
Biochemical Explanation for ADHD
The biochemical explanation for Attention-Deficit Hyperactivity Disorder (ADHD) is complex and involves multiple neurotransmitter systems, particularly dopamine and norepinephrine.
- Dopamine and norepinephrine deficits are thought to be the neurochemical basis of ADHD, as medications used to treat ADHD, such as methylphenidate, amphetamine, and atomoxetine, indicate an increase in these neurotransmitters 3.
- The etiology of ADHD is more complex and likely involves many genes of small individual effect, as well as differences in brain structure, including the frontal lobes, caudate nucleus, and cerebellar vermis 4.
- Altered reinforcement mechanisms, particularly sensitivity to delay of reinforcement, may play a central role in the symptoms of ADHD, with dopamine cell firing activity associated with reinforcing events 4.
- Medications such as D-amphetamine, methylphenidate, and atomoxetine have distinct pharmacological actions on dopaminergic and noradrenergic neurotransmission, which may impact their therapeutic effects in the treatment of ADHD 5.
Key Findings
- Studies have shown that ADHD is associated with impaired function and increased risk of poor outcomes in children, young people, and adults with the condition 6, 7.
- Medications used to treat ADHD have been shown to be effective in treating symptoms and improving functional outcomes, but their mechanisms of action are not fully understood 6, 3.
- Further research is needed to understand the mechanisms of action of these medications and how they improve symptoms, as well as to examine their effects on commonly occurring comorbidities 6, 7.