Non-Stimulant Medications for ADHD
The FDA-approved non-stimulant medications for ADHD include atomoxetine (Strattera), guanfacine extended-release (Intuniv), and clonidine extended-release (Kapvay), with atomoxetine being a norepinephrine reuptake inhibitor and the alpha-2 agonists (guanfacine and clonidine) working through enhanced noradrenergic neurotransmission in the prefrontal cortex 1, 2.
Three Main Classes of Non-Stimulants
1. Norepinephrine Reuptake Inhibitors
Atomoxetine is the most extensively studied non-stimulant for ADHD 2:
- Mechanism: Selectively inhibits norepinephrine reuptake
- Dosing: Can be given once daily or split into morning/evening doses; evening-only dosing is also an option to reduce daytime side effects
- Onset: Takes 6-12 weeks to achieve full therapeutic effect 2
- Major adverse effects: Decreased appetite, headache, stomach pain
- Critical monitoring: Suicidality, clinical worsening, pulse 2
Viloxazine extended-release is a newer norepinephrine reuptake inhibitor recently approved for ADHD 3, 4.
2. Alpha-2 Adrenergic Agonists
Guanfacine extended-release 2:
- Mechanism: Agonism at alpha-2A adrenergic receptors in the prefrontal cortex, strengthening top-down regulation of attention and working memory
- Dosing: Weight-based (0.1 mg/kg rule of thumb), once-daily; available in 1,2,3, and 4 mg tablets
- Onset: 2-4 weeks for full effect 2
- Major adverse effects: Somnolence, fatigue, irritability, insomnia, nightmares
- Monitoring: Pulse, blood pressure (risk of hypotension/bradycardia) 2
Clonidine extended-release 2:
- Mechanism: Similar alpha-2 agonism but approximately 10 times more potent than guanfacine
- Dosing: Start 0.1 mg at bedtime, can increase to twice-daily; maximum 0.4 mg/day; also available as transdermal patch (0.1,0.2,0.3 mg)
- Onset: 2-4 weeks 2
- Major adverse effects: Similar to guanfacine but with additional dry mouth, sedation, bradycardia, and syncope
- Note: Requires twice-daily dosing (disadvantage compared to guanfacine) 2
Clinical Positioning
Non-stimulants are generally recommended as second-line treatment after stimulants, with smaller effect sizes (medium range) compared to stimulants' large effect sizes 2. However, they serve as first-line options in specific clinical scenarios 2:
- Substance use disorders (stimulants pose diversion/abuse risk)
- Disruptive behavior disorders or oppositional defiant disorder
- Tic disorders or Tourette's syndrome
- Comorbid sleep disturbances (particularly clonidine and guanfacine)
- Comorbid anxiety or autism spectrum disorder (atomoxetine has supporting evidence)
Key Advantages Over Stimulants
- "Around-the-clock" effects without rebound symptoms in afternoon/evening 2
- Uncontrolled substances (no DEA scheduling, lower diversion risk) 2
- Fewer appetite/growth concerns with atomoxetine compared to stimulants 2
- Can augment stimulant therapy: In the U.S., guanfacine and clonidine are approved as adjunctive therapy to reduce stimulant side effects (sleep disturbances, elevated blood pressure/heart rate) or enhance efficacy 2
Critical Caveats
Delayed onset is the major limitation: Unlike stimulants with immediate effects, atomoxetine requires 6-12 weeks and alpha-2 agonists need 2-4 weeks before observing therapeutic benefits 2. This necessitates patient/family counseling about realistic expectations.
Evening administration is preferable for clonidine and guanfacine due to frequent somnolence/sedation, though atomoxetine can also be dosed in the evening if daytime side effects are problematic 2.
Within non-stimulants, atomoxetine has less frequent and less pronounced adverse effects compared to the alpha-2 agonists 2.
Cardiovascular monitoring is essential for all non-stimulants, particularly the alpha-2 agonists which carry warnings for hypotension, bradycardia, and cardiac conduction abnormalities 2.