Can Fluvoxamine Cause Drowsiness?
Yes, fluvoxamine can cause somnolence (drowsiness), though it can also paradoxically cause insomnia in some patients.
Key Evidence on Somnolence
According to FDA labeling data, somnolence occurred in 22% of patients taking fluvoxamine compared to 8% on placebo in controlled trials 1. This represents a nearly 3-fold increased risk. Notably, somnolence was common enough that 4% of patients discontinued fluvoxamine specifically due to somnolence 1.
In a large postmarketing safety database of 24,624 patients, somnolence occurred in 6.9% of patients, making it the second most common adverse effect after nausea 2. Among SSRIs specifically, fluvoxamine ranked highest for causing somnolence with an odds ratio of 6.32 compared to placebo 3.
The Paradox: Insomnia vs. Somnolence
Fluvoxamine exhibits a bidirectional effect on sleep:
- Insomnia also occurs frequently, affecting 21% of patients versus 10% on placebo 1
- This dual effect is characteristic of SSRIs as a class, which can cause "insomnia or somnolence" 4
- The specific effect experienced appears to vary by individual patient factors
Clinical Implications
When counseling patients:
- Warn them that drowsiness is a common side effect occurring in approximately 1 in 5 patients
- Explain that the opposite effect (insomnia) can also occur
- Advise caution with activities requiring alertness (driving, operating machinery) until they know how the medication affects them
- Consider timing of dosing: the drug can be given at bedtime if somnolence predominates, or in the morning if insomnia is the issue 5
Important drug interaction: Fluvoxamine clearance is significantly reduced when combined with ciprofloxacin, which can increase sedation risk 6.
Overdose Considerations
In overdose situations, somnolence is one of the most common presenting symptoms (≥5% of cases), along with coma in severe cases 1. This underscores the drug's sedating potential at higher concentrations.