Gabapentin and Urinary Retention
Gabapentin can cause urinary retention and has been identified as a new safety signal in pharmacovigilance databases, though this adverse effect is not widely recognized or listed in many product labels. 1
Evidence for Gabapentin-Induced Urinary Retention
The strongest evidence comes from a 2022 analysis of Italy's national adverse drug reaction database, which identified gabapentin as one of five drugs with statistically significant disproportionality signals for urinary retention—notably, this side effect was not even described in gabapentin's summary of product characteristics at the time of analysis. 1 This represents high-quality pharmacovigilance data suggesting an under-recognized risk.
Clinical Presentation and Mechanism
Gabapentin can cause both urinary incontinence and urinary retention, representing opposite ends of bladder dysfunction:
- Overflow urinary incontinence has been documented in multiple case reports, with onset typically occurring 7-10 days after starting gabapentin therapy. 2, 3
- One case specifically described overflow incontinence at 1200 mg/day that resolved when the dose was reduced to 600 mg/day, suggesting a dose-dependent effect. 3
- The median time to urinary retention onset across all drugs in the Italian database was 7 days (IQR 1-47.5 days), consistent with gabapentin's timeline. 1
A critical caveat: Gabapentin has also been studied as a treatment for neurogenic overactive bladder, showing efficacy in reducing detrusor overactivity in 16 patients with neurological conditions. 4 This paradoxical effect highlights that gabapentin's impact on bladder function may depend on the underlying pathophysiology—it may help overactive bladders while potentially causing retention in normal bladders.
High-Risk Populations
Patients at elevated risk for gabapentin-induced urinary retention include:
- Older adults (median age 67 years in the pharmacovigilance analysis), particularly men with benign prostatic hyperplasia (present in one-third of male patients experiencing drug-induced urinary retention). 1
- Patients with diabetes mellitus (13.8% of urinary retention cases had diabetes). 1
- Those with pre-existing bladder disorders (5% of cases). 1
- Patients with renal impairment, as gabapentin clearance is entirely renal and impaired kidney function leads to higher plasma concentrations and prolonged half-life. 5, 6
Monitoring and Management Recommendations
Before initiating gabapentin, assess for:
- History of urinary retention or obstructive urinary symptoms
- Benign prostatic hyperplasia in men
- Concurrent use of other medications that impair bladder function (anticholinergics, antimuscarinics, tricyclic antidepressants, antipsychotics)
- Renal function via creatinine clearance calculation 5
If urinary retention develops:
- Discontinue or reduce gabapentin dose immediately—symptoms resolved within 1-7 days after stopping the drug in reported cases. 2
- Consider switching to pregabalin, which achieved pain control without recurrence of urinary retention in one documented case despite similar pharmacology. 3
- Start with lower doses (100-300 mg) and titrate slowly in high-risk patients. 5
Important clinical pitfall: The urinary retention risk is not mentioned in many gabapentin product labels, so clinicians must maintain high clinical suspicion when patients on gabapentin develop new urinary symptoms. 1