Background: Anxiety in relation to surgery is a well-known problem. Melatonin offers an atoxic alternative to benzodiazepines in ameliorating this condition in the pre- and postoperative period.
Objectives: To assess the effect of melatonin on pre- and postoperative anxiety in adults when comparing melatonin with placebo or when comparing melatonin with benzodiazepines.
Search methods: The following databases were searched on 19 April 2013: CENTRAL, MEDLINE, EMBASE, CINAHL and Web of Science. For ongoing trials and protocols we searched clinicaltrials.gov, Current Controlled Trials and the World Health Organization (WHO) International Clinical Trials Registry Platform. We reran the search in October 2014. We will deal with any studies of interest when we update the review.
Selection criteria: Randomized, placebo-controlled or standard treatment-controlled, or both, studies that evaluated the effect of preoperatively administered melatonin on preoperative or postoperative anxiety. We included adult patients of both genders (15 to 90 years of age) undergoing any kind of surgical procedure in which it was necessary to use general, regional or topical anaesthesia.
Data collection and analysis: Data were extracted independently by two review authors. Data extracted included information about study design, country of origin, number of participants and demographic details, type of surgery, type of anaesthesia, intervention and dosing regimen, preoperative anxiety outcome measures and postoperative anxiety outcome measures.
Main results: This systematic review identified 12 randomized controlled trials (RCTs) including 774 patients that assessed melatonin for treating preoperative anxiety, postoperative anxiety or both. Four of the 12 studies compared melatonin, placebo and midazolam, whereas the remaining eight studies compared melatonin and placebo only.The quality of the evidence for our primary outcome (melatonin versus placebo for preoperative anxiety) was high. More than half of the included studies had a low risk of selection bias and at least 75% of the included studies had a low risk of attrition, performance and detection bias. Most of the included studies had an unclear risk of reporting bias.Eight out the 10 studies that assessed the effect of melatonin on preoperative anxiety using a visual analogue scale (VAS) (ranging from 0 to 100 mm, higher scores indicate greater anxiety) showed a reduction compared to placebo. The reported estimate of effect (relative effect -13.36, 95% confidence interval (CI) -16.13 to -10.58; high quality evidence) was based on a meta-analysis of seven studies. Two studies did not show any difference between melatonin and placebo. Two studies comparing melatonin with midazolam using a VAS found no evidence of a difference in preoperative anxiety between the two groups (relative effect -1.18, 95% CI -2.59 to 0.23; low quality evidence).Eight studies assessed the effect of melatonin on postoperative anxiety. Four of these studies measuring postoperative anxiety 90 minutes postoperatively using a VAS did not find any evidence of a difference between melatonin and placebo (relative effect -3.71, 95% CI -9.26 to 1.84). Conversely, two studies showed a reduction of postoperative anxiety measured six hours after surgery using the State-Trait Anxiety Inventory (STAI) when comparing melatonin with placebo (relative effect -5.31, 95% CI -8.78 to -1.84; moderate quality evidence). Two studies comparing melatonin with midazolam using a VAS did not find any evidence of a difference between the two groups in postoperative anxiety (relative effect -2.02, 95% CI -5.82 to 1.78).
Authors' conclusions: When compared to placebo, melatonin given as premedication (tablets or sublingually) can reduce preoperative anxiety in adults (measured 50 to 100 minutes after administration). Melatonin may be equally as effective as standard treatment with midazolam in reducing preoperative anxiety in adults (measured 50 to 100 minutes after administration). The effect of melatonin on postoperative anxiety (measured 90 minutes and 6 hours after surgery) in adults is mixed but suggests an overall attenuation of the effect compared to preoperatively.