Oseltamivir Does Not Cause Constipation
Constipation is not a recognized adverse effect of oseltamivir. The primary gastrointestinal side effects are nausea and vomiting, not constipation.
Documented Adverse Effects of Oseltamivir
Gastrointestinal Effects
The most common adverse effects of oseltamivir are gastrointestinal, but these specifically involve the upper GI tract:
- Nausea occurs in approximately 10% of adults (compared to 6% with placebo) 1, 2
- Vomiting occurs in approximately 9% of adults (compared to 3% with placebo) and 14% of children (compared to 8.5% with placebo) 1, 2
- Diarrhea is reported in less than 5% of patients, not constipation 1, 2
- These gastrointestinal symptoms are typically mild, transient, and can be reduced by taking the medication with food 1, 2, 3
Other Common Adverse Effects (All <5%)
The documented adverse effects from clinical trials include 1:
- Headache
- Dizziness
- Nasal symptoms
- Sinusitis
- Bronchitis
- Cough
- Ear, nose, and throat infections
Constipation is notably absent from all guideline-documented adverse effect profiles across multiple ACIP recommendations spanning 2002-2007 1.
Clinical Implications
If a patient taking oseltamivir develops constipation, alternative explanations should be considered:
- Dehydration from influenza illness itself (fever, decreased oral intake)
- Reduced physical activity during illness
- Other concurrent medications
- Pre-existing gastrointestinal conditions
The comprehensive safety data from over 11,000 subjects in clinical trials and postmarketing surveillance of over 4 million prescriptions has not identified constipation as an adverse effect 4.