Amitriptyline Does NOT Cause Increased Urinary Frequency
Amitriptyline, as a tricyclic antidepressant with strong anticholinergic properties, typically causes urinary retention and decreased urinary frequency, not increased frequency. 1
Mechanism of Action on Urinary Function
- Amitriptyline blocks muscarinic M1 receptors, producing anticholinergic effects that reduce bladder contractility and increase bladder capacity, leading to urinary retention rather than frequency 2
- The FDA drug label explicitly lists urinary retention and dilatation of the urinary tract as anticholinergic adverse reactions, not increased frequency 1
- This anticholinergic effect is precisely why amitriptyline is therapeutically used to treat urinary frequency in conditions like interstitial cystitis/bladder pain syndrome 3, 4
Clinical Evidence Supporting Decreased Frequency
- In a randomized controlled trial of 48 patients with interstitial cystitis, amitriptyline improved urinary frequency compared to placebo, though the difference did not reach statistical significance (p = 0.063) 5
- A multicenter trial of 271 treatment-naïve patients with interstitial cystitis/painful bladder syndrome showed that amitriptyline at doses ≥50 mg daily resulted in 66% response rate for symptom improvement, which included reduction in frequency 6
- A case series of 22 patients with urinary frequency treated with amitriptyline 25-100 mg showed that 11 became symptom-free and 6 showed significant improvement in their frequency symptoms 4
Important Clinical Caveat
If a patient on amitriptyline reports increased urinary frequency, consider alternative explanations:
- Paradoxical overflow incontinence from urinary retention—the anticholinergic effect may cause incomplete bladder emptying with subsequent overflow and frequent small voids 1
- Post-void residual urine should be measured to exclude this complication 3
- Concurrent urinary tract infection, which can occur when urinary retention leads to stasis 3
- An unrelated condition causing the frequency that is coincidental to amitriptyline use
Monitoring Recommendations
- The International Children's Continence Society recommends that when anticholinergics (including tricyclics) are used, post-void residual urine must be monitored because retention can lead to UTIs 3
- Patients must maintain sound voiding habits and report dysuria or unexplained fever immediately 3
- If urinary retention develops, the dose should be reduced or the medication discontinued 1