Does Fluoxetine (Prozac) Cause Drowsiness?
Fluoxetine is more likely to cause insomnia and nervousness than drowsiness, though somnolence can occur as a less common side effect. 1, 2, 3
Primary Sleep Effects
Fluoxetine typically has activating rather than sedating properties:
- Insomnia and nervousness are reported more frequently with fluoxetine than with tricyclic antidepressants 3
- Fluoxetine is classified as a "nonsedative antidepressant" and is listed among SSRIs that are "sleep-disturbing early in treatment" 4, 5
- The American Academy of Sleep Medicine identifies SSRIs including fluoxetine as medications that can contribute to insomnia 1
When Somnolence Does Occur
While less common than insomnia, somnolence is a recognized side effect:
- In acute overdose studies, drowsiness/somnolence was observed in approximately 21% (14/67) of adult patients who ingested fluoxetine alone 6
- The FDA label lists somnolence among documented adverse effects in overdose cases 2
- Among common side effects across second-generation antidepressants, somnolence is reported, though nausea, nervousness, and insomnia are more characteristic of fluoxetine specifically 1
Clinical Implications
Timing matters for sleep-related side effects:
- Sleep disturbances from fluoxetine are most prominent early in treatment and tend to diminish over several weeks 4
- Fluoxetine does not typically exacerbate sleep disturbance at Week 1 or endpoint in patients with baseline insomnia 5
- The drug's effects on REM sleep (suppression) are consistent but subjective sleep quality often improves during 3-4 weeks of effective treatment 4
Practical Management
If a patient reports feeling sleepy on fluoxetine:
- Consider timing of administration - taking fluoxetine in the morning may reduce any sedating effects
- Evaluate for co-ingested substances or other medications that may contribute to drowsiness 6
- Assess whether fatigue (low energy, physical tiredness) is being confused with true sleepiness (tendency to fall asleep), as fatigue is more common than actual sleepiness in patients taking antidepressants 1
- Rule out worsening depression or other sleep disorders, as the presence of significant sleepiness should prompt investigation for alternative causes 1
The bottom line: While somnolence can occur, fluoxetine is far more likely to cause the opposite problem—insomnia and activation—particularly in the first weeks of treatment. 1, 4, 3