Can Aricept (donepezil) cause drowsiness?

Drowsiness as a Side Effect of Aricept (Donepezil)

Aricept (donepezil) can cause drowsiness in some patients, though it is not among the most common side effects of the medication. 1

Side Effect Profile of Donepezil

Donepezil's side effect profile primarily reflects its cholinergic mechanism of action, with the most common adverse reactions including:

• Most common side effects (occurring in ≥5% of patients on 10mg/day and at twice the placebo rate):

  • Nausea (11% vs 6% placebo)
  • Diarrhea (10% vs 5% placebo)
  • Insomnia (9% vs 6% placebo)
  • Vomiting (5% vs 3% placebo)
  • Muscle cramps (6% vs 2% placebo)
  • Fatigue (5% vs 3% placebo)
  • Anorexia (4% vs 2% placebo) 1

• Drowsiness/somnolence is reported in approximately 2% of patients taking donepezil compared to <1% in those taking placebo. 1

Timing of Administration and Sleep Effects

The timing of donepezil administration may impact sleep quality:

• Research suggests that morning administration of acetylcholinesterase inhibitors like donepezil may improve sleep quality compared to nighttime administration. 2
• In one study, patients who switched from nighttime to morning donepezil administration showed significant improvements in sleep quality (p=0.046) and reduced daytime drowsiness (p<0.001). 2

Factors That May Influence Drowsiness

Several factors may contribute to drowsiness in patients taking donepezil:

1. Dose-related effects: Higher doses (10mg) are associated with more side effects than lower doses (5mg). 1

2. Titration schedule: Slower titration (6 weeks vs 1 week) to reach 10mg/day is associated with fewer adverse effects. 1

3. Individual patient factors:

   • Elderly patients may be more sensitive to side effects
   • Patients with hepatic impairment may experience more pronounced effects 3

Management of Drowsiness

If drowsiness occurs while taking donepezil:

1. Consider timing of administration:

   • Switching from nighttime to morning dosing may improve sleep quality and reduce daytime drowsiness 2

2. Dose adjustment:

   • Starting with 5mg daily and gradually titrating to 10mg may reduce side effects 1

3. Evaluate continued therapy:

   • Beneficial response should be evaluated after 6-12 months
   • Consider stopping medication if side effects don't resolve 4

Clinical Considerations

• Most adverse effects with donepezil are transient and resolve with continued treatment without dose modification 1
• Drowsiness is not among the most common reasons for discontinuation of donepezil therapy 1
• When prescribing donepezil, be aware of potential polypharmacy issues in older adults, as it appears on tables of medications that may require special consideration in this population 3

Conclusion

While drowsiness is not among the most frequently reported side effects of donepezil, it can occur in approximately 2% of patients. Morning administration rather than nighttime dosing may help mitigate sleep disturbances and daytime drowsiness in patients taking this medication.