What are the side effects of atomoxetine (Strattera)?

Side Effects of Atomoxetine (Strattera)

Atomoxetine commonly causes nausea, vomiting, fatigue, decreased appetite, abdominal pain, and somnolence in children and adolescents, while adults may experience dry mouth, insomnia, nausea, decreased appetite, constipation, urinary difficulties, and sexual dysfunction. 1, 2

Common Side Effects

In Children and Adolescents:

• Gastrointestinal effects:

  • Abdominal pain (18% vs 10% placebo)
  • Vomiting (11% vs 6% placebo)
  • Nausea (10% vs 5% placebo)
  • Constipation (2% vs 1% placebo) 1, 2

• General effects:

  • Fatigue (8% vs 3% placebo)
  • Irritability (6% vs 3% placebo)
  • Decreased appetite (16% vs 4% placebo)
  • Weight loss (3% vs 0% placebo) 2

• Neurological effects:

  • Somnolence/sedation (11% vs 4% placebo)
  • Dizziness (5% vs 2% placebo) 1, 2

In Adults:

• Dry mouth
• Insomnia
• Nausea
• Decreased appetite
• Constipation
• Urinary retention/difficulties with micturition
• Erectile disturbance
• Dysmenorrhea
• Dizziness
• Decreased libido
• Sexual dysfunction (approximately 2% of patients) 3, 4, 5

Serious Side Effects and Warnings

Suicidality Risk

• FDA black box warning for increased risk of suicidal ideation in children and adolescents 6
• Based on analysis of twelve placebo-controlled trials showing greater risk during treatment 1
• All children treated with atomoxetine should be monitored closely for:
  • Suicidality
  • Clinical worsening
  • Unusual changes in behavior
  • Especially during first few months of treatment or dose changes 1, 6

Cardiovascular Effects

• Modest increases in heart rate and blood pressure 4, 7
• Use with caution in patients with:
  • Hypertension
  • Significant cardiovascular disorders 3
• Regular monitoring of blood pressure and heart rate is essential 6

Other Warnings

• Liver injury: Rare but serious liver injury has been reported 7
• Growth effects: May affect height and weight, particularly during initial treatment 1, 7
• Priapism: Risk of prolonged and painful erections 1
• Psychiatric effects:
  • Emergent psychotic or manic symptoms
  • Aggression or hostility
  • Mood swings 1, 2

Metabolizer Status Considerations

• Approximately 7% of the population are poor metabolizers of atomoxetine via CYP2D6 pathway 1
• Poor metabolizers experience:
  • Significantly higher plasma levels
  • Longer half-lives
  • Potentially increased adverse effects 1
  • Higher rates of insomnia (11% vs 6% in extensive metabolizers)
  • Weight decrease (7% vs 4%)
  • Constipation (7% vs 4%)
  • Depression (7% vs 4%)
  • Tremor (5% vs 1%) 2

Discontinuation Rates and Timing

• In clinical trials, discontinuation rates due to adverse effects:
  • Children/adolescents: 3% of atomoxetine subjects vs 1.4% of placebo subjects 2
  • Adults: 11.3% of atomoxetine subjects vs 3.0% of placebo subjects 2
• Most side effects are mild to moderate and transient 8
• Side effects appear to be dose-dependent, with higher discontinuation rates at dosages greater than 1.5 mg/kg/day 3

Drug Interactions

• Selective serotonin reuptake inhibitors (particularly paroxetine, fluoxetine) can elevate serum atomoxetine levels 1, 2
• Other CYP2D6 inhibitors (e.g., quinidine) may increase atomoxetine levels 2

Understanding these side effects is crucial for monitoring patients on atomoxetine therapy, particularly during the initial treatment period and dose adjustments when adverse effects are most likely to occur.