Objective. – To evaluate the prevalence of adverse effects of opioids used to treat acute nonmalignant musculoskeletal pain.

Methods. – Prospective, single-center, observational study in patients admitted to a rheumatology department for a nonmalignant painful musculoskeletal condition with onset within the last 3 months and a need for WHO Class III analgesics. The following side effects were recorded daily: nausea and vomiting, constipation, pruritus, urinary retention, drowsiness, confusion, and hallucinations.

Results. – The 75 study patients (46 women and 29 men with a mean age of 56.4 years) were admitted for nerve root pain, osteoporotic vertebral fracture, inflammatory joint disease, or other disorders. First-line treatment was sustained-release morphine sulfate in a mean starting dosage of 55.2 mg/day. The dosage was increased if needed (mean maximum dosage, 78.3 mg/day). Mean treatment duration was 8.9 days. Adverse effects were recorded in 73.3% of patients but were usually minor, requiring no change in the treatment regimen. Eight patients experienced serious adverse effects (confusion in five and urinary retention in three) that resolved with no change in treatment in two patients, after dosage reduction in two patients and after substitution of fentanyl or hydromorphone hydrochloride in four patients. Treatment discontinuation was not associated with adverse effects.

Conclusions. – Morphine is often responsible for adverse effects in patients with acute nonmalignant musculoskeletal pain. These effects are usually moderate and very rarely require discontinuation of the drug.