Seven trials (10 comparisons) were included (503 patients). Two trials scored 2, one trial scored 4, and four trials scored 5 on the Jadad scale.
The meta-analysis revealed a significant delay in the time to first analgesic request with intrathecal morphine plus clonidine 90 to 150 micrograms (μg), compared with intrathecal morphine alone (MD 1.73 hours, 95% CI 1.29 to 2.18; Ι²=0; one RCT; two comparisons). It also showed that clonidine 90μg to 150μg reduced the amount of postoperative morphine (MD -4.68mg, 95% CI -6.00 to -3.36; Ι²=8%; two RCTs).
No significant differences between the two groups were found for clonidine 25μg to 30μg, and 50μg to 75μg, for postoperative morphine.
There were no statistically significant differences in adverse effects (nausea and vomiting, over-sedation, respiratory depression, and pruritis) between patients with or without clonidine, apart from a statistically significant increase in hypotension (OR 1.78, 95% CI 1.02 to 3.12; Ι²=0; four RCTs).
The results of the sensitivity analyses were reported. There was no evidence of publication bias.