Opioids learning module

4.6. Other adverse effects

Opioids can cause bladder dysfunction and the effects can range from difficulty in voiding to urinary retention; these adverse effects often occur after surgery. Tolerance to these opioid effects develops on longer use.

Constriction of the pupil—miosis—results from opioid stimulation of the parasympathetic nervous system; pinpoint pupils are characteristic of opioid poisoning.

Factors which increase risk

Urinary retention is more often associated with epidural injection rather than intravenous or intramuscular injection. Take care in those susceptible to urinary disorders including patients with prostatic hypertrophy and the elderly. Concurrent use of an antimuscarinic (anticholinergic) drug may increase the risk of urinary retention.


In severe cases of urinary retention, bladder catheterisation may be needed. The opioid antagonist naloxone may be able to reverse the urinary effects of opioids.

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Page last modified: 17 February 2015