Can melatonin help with jet lag or shift work?

Yes. The current evidence suggests that melatonin can ease sleep problems associated with jet lag. In situations where external stimuli (sunlight and darkness cycles) and internal stimuli (the internal clock) are not in sync, supplemental melatonin is thought to help re-establish this synchronization. A Cochrane meta-analysis of 10 studies which examined jet lag due to flights traversing five or more time zones found that melatonin taken at the destination bedtime was significantly more effective than placebo at normalizing circadian rhythm and reducing symptoms of jet lag. One of these studies found that doses of 500 mcg (0.5 mg) and 5 mg were similarly effective at reducing jet lag, but participants reported falling asleep faster with the 5 mg dose. The two studies in the meta-analysis reporting individual statistics found that about 17% of participants still experienced severe jet lag after taking melatonin, compared to 67% after taking a placebo.^[1]

Overall, melatonin seems to be helpful to re-establish a healthy circadian rhythm after experiencing jet lag. Interestingly, melatonin could also be used to treat social jet lag (when changes in sleep habits over the weekend disrupt sleep the following week).^[2] Future studies may shed more light on this.