Monaz: Hello, I'm Monaz Mehta, editor in the Cochrane Editorial and Methods department. The Cochrane Anaesthesia Group has produced a wide variety of reviews relevant to procedures related to surgery. One of these looks at the use of melatonin for preoperative and postoperative anxiety in adults and it was updated in December 2020. We asked the new lead author, Bennedikte Madsen, from the Center for Perioperative Optimizationin Herlev Hospital in Denmark to tell us about the latest findings.

Bennedikte: Perioperative anxiety is a well-known problem and various studies have shown that it can affect 11% up to 80% of people. It's more common for younger people and women, and the type of surgery and anesthesia, and cultural and religious differences can also affect its prevalence. The anxiety is often treated with benzodiazepines, but these drugs have a wide range of side effects, including impairment of psychomotor and cognitive function, even if only a single dose is used.
One possible alternative is melatonin, which is a hormone produced in the pineal gland located deep in the brain. This has been shown to reduce anxiety in several studies. It also has no, or only mild or short-term side effects, making it a useful candidate for easing anxiety in people having surgery; and our review suggests that it is effective.
We set out to assess the effects of melatonin on preoperative and postoperative anxiety in adults, when compared to placebo or benzodiazepines.
The previous version of the review, in 2015, had 12 randomized trials but we are now able to include 27. There are now 24 trials comparing melatonin with placebo and 11 compare melatonin versus a benzodiazepine, with some trials making both comparisons.
In our meta-analysis of data from nearly 1300 patients in 18 trials of melatonin versus placebo, we found moderate certainty evidence of a decrease in preoperative anxiety in the melatonin group. We also found that melatonin decreased postoperative anxiety compared with placebo, but this decrease was smaller and might not be clinically relevant. 
When comparing melatonin with benzodiazepines, we found little or no difference on preoperative and postoperative anxiety, suggesting that melatonin may be equally as effective as benzodiazepines. 
In summary, when compared with placebo, melatonin given before surgery reduces preoperative anxiety in adults, which is potentially clinically relevant. There was also some effect of melatonin on postoperative anxiety when compared to placebo, but this was much smaller. While the lack of difference in anxiety between melatonin and benzodiazepines, suggests that melatonin may have a similar effect to these commonly used drugs in reducing preoperative and postoperative anxiety in adults.

Monaz: If you would like to look further into these results, or check for further updates to this review as more evidence becomes available, it's available in full at Cochrane Library dot com. If you go to the website and type 'melatonin and surgery' into the search box, you'll find it.