Injected morphine in postoperative pain: a quantitative systematic review

J Pain Symptom Manage. 1999 Mar;17(3):164-74. doi: 10.1016/s0885-3924(98)00126-2.


This systematic review of single-dose, placebo-controlled, randomized trials assessed pain relief from subcutaneous, intramuscular or intravenous morphine compared with placebo in postoperative pain. Pain relief or pain intensity difference over 4 to 6 hours was extracted and converted into the number of patients with at least 50% pain relief. This was used to calculate the relative benefit and the number-needed-to-treat (NNT) for one patient to achieve at least 50% pain relief. In 15 trials, comparing intramuscular morphine 10 mg (486 patients) with placebo (460 patients) morphine had an NNT of 2.9 (95% confidence interval 2.6-3.6). This meant that one of every three patients with moderate or severe postoperative pain treated with 10 mg intramuscular morphine had at least 50% pain relief, and would not have achieved this had they been given placebo. Minor adverse effects were more common with morphine (34%) than with placebo (23%) (relative risk 1.49 [1.09-2.04]), but drug related study withdrawal was rare (1.2% overall) and no different from placebo.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review
  • Systematic Review

MeSH terms

  • Analgesics, Opioid / administration & dosage
  • Analgesics, Opioid / therapeutic use*
  • Humans
  • Injections, Intramuscular
  • Injections, Intravenous
  • Injections, Subcutaneous
  • Morphine / administration & dosage
  • Morphine / therapeutic use*
  • Pain, Postoperative / drug therapy*
  • Randomized Controlled Trials as Topic


  • Analgesics, Opioid
  • Morphine