Can fluoxetine (Prozac) cause nocturnal vomiting and a sweet taste in the mouth?

Can Fluoxetine (Prozac) Cause Nocturnal Vomiting and Sweet Taste in the Mouth?

Yes, fluoxetine can cause vomiting, including at night, as it is one of the most common gastrointestinal side effects of this medication, though a sweet taste in the mouth is not a recognized adverse effect of fluoxetine. 1, 2

Vomiting as a Known Side Effect

• Nausea and vomiting are well-established adverse effects of fluoxetine, occurring commonly enough to be among the most frequent reasons for treatment discontinuation in clinical trials with related serotonergic antidepressants 3
• The gastrointestinal effects are dose-related and occur more frequently at higher doses (above the standard 20 mg/day) 1, 2
• In overdose studies, vomiting was documented in approximately 4-6% of patients who ingested fluoxetine alone 4
• These gastrointestinal symptoms are referable to fluoxetine's mechanism as a selective serotonin reuptake inhibitor, which increases serotonin availability throughout the body, including in the GI tract 1

Timing of Vomiting

• While nocturnal vomiting specifically is not highlighted in the literature, vomiting can occur at any time during fluoxetine treatment 1, 2
• The timing may relate to when the medication is taken, as fluoxetine reaches peak plasma concentration (Tmax) between 4-8 hours after oral administration 1
• If the patient takes fluoxetine in the evening, nocturnal symptoms would be more likely during this peak concentration window

Sweet Taste in Mouth

• A sweet taste in the mouth is NOT a documented side effect of fluoxetine in any of the available safety literature 1, 2
• This symptom warrants evaluation for alternative causes, including:
  • Metabolic conditions (hyperglycemia/diabetes)
  • Gastroesophageal reflux disease (GERD), which can coexist with medication-induced nausea
  • Other medications the patient may be taking
  • Oral or dental conditions

Clinical Considerations

• The combination of nocturnal vomiting with an unusual taste suggests the need to rule out other causes beyond fluoxetine alone 2
• Common fluoxetine side effects include nausea, anxiety, insomnia, anorexia, diarrhea, nervousness, and headache—but not taste alterations 1
• If vomiting is severe or persistent, consider dose reduction or medication change, as fluoxetine is generally well-tolerated at the standard 20 mg/day dose 2
• Fluoxetine's long half-life (4 days after chronic dosing, with active metabolite norfluoxetine having a 7-day half-life) means side effects may persist for weeks after discontinuation 1

Important Drug Interaction

• If the patient is receiving chemotherapy with ondansetron (a 5-HT3 antagonist antiemetic), fluoxetine may reduce ondansetron's antiemetic effectiveness by increasing serotonin levels that compete at receptor sites 5
• This interaction has been clinically observed and could paradoxically worsen chemotherapy-related nausea and vomiting 5