Opioid therapy for chronic noncancer pain (CNCP) is controversial due to concerns
regarding long-term efficacy and adverse events (including addiction). We systematically
reviewed the clinical evidence on patients treated with opioids for CNCP for at least
six months. Of 115 studies identified by our search of eleven databases (through April
7, 2007), 17 studies (patients [n]=3,079) met inclusion criteria. Studies evaluated
oral (studies [k]=7; n=1,504), transdermal (k=3; n=1, 993), and/or intrathecal (k=8;
n=177) opioids. Many patients withdrew from the clinical trials due to adverse effects
(oral: 32.5% [95% confidence interval (CI), 26.1%-39.6%]; intrathecal: 6.3% [95% CI,
2.9%-13.1%]; transdermal: 17.5% [95% CI, 6.5%-39.0%]), or due to insufficient pain
relief (oral: 11.9% [95% CI, 7.8%-17.7%]; intrathecal: 10.5% [95% CI, 3.5%-27.4%];
transdermal: 5.8% [95% CI, 4.2%-7.3%]). Signs of opioid addiction were reported in
only 0.05% (1/2,042) of patients and abuse in only 0.43% (3/685). There was an insufficient
amount of data on transdermal opioids to quantify pain relief. For patients able to
remain on oral or intrathecal opioids for at least six months, pain scores were reduced
long-term (oral: standardized mean difference [SMD] 1.99, 95% CI, 1.17-2.80; intrathecal:
SMD 1.33, 95% CI, 0.97-1.69). We conclude that many patients discontinue long-term
opioid therapy due to adverse events or insufficient pain relief; however, weak evidence
suggests that oral and intrathecal opioids reduce pain long-term in the relatively
small proportion of individuals with CNCP who continue treatment.