4. Principal risks and risk-reduction measures

Some noteworthy risks of opioids are discussed in this module. Summaries of product characteristics and the BNF should be consulted for a fuller account of the adverse effects and warnings for individual opioids.

Note. Some advice in this module may not apply in the palliative care setting. Also, the module does not cover infrequent effects which occur on chronic treatment, such as hyperalgesia1, myoclonus2, and endocrine derangement.

Very common (> 10%) and common (1–10%) adverse effects:

Infrequent but potentially serious adverse effects:

  • Ileus5
  • Convulsions
  • Bradycardia
  • Respiratory depression
  • dependence6 and withdrawal

Important drug interactions

Pregnancy and breastfeeding


  1. Exaggerated sensitivity to a normally painful stimulus
  2. Brief, involuntary twitching of the muscles which may produce a spasmodic or jerking movement
  3. Feeling of dissatisfaction, anxiety and restlessness
  4. Constriction of the pupil of the eye, often as a side-effect of certain drugs
  5. Partial or complete non-mechanical blockage of the small intestine, or large intestine, or both
  6. Dependence is a state that develops as a result of repeated use of a certain chemical substance (eg alcohol, benzodiazepine, opioid, or even medicines for reducing blood pressure). It represents the resetting of homeostasis because of the persisting presence of the chemical substance