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How do you sleep after jet lag?
To avoid light in the morning, stay indoors, such as by going to a mall or a museum. If you flew west, stay awake during daylight, and try to sleep after dark. This may help adjust your body clock and help your body make melatonin at the right time.
Does melatonin help with jet lag?
Supplemental melatonin is commonly used for jet lag treatment; it's been shown to help with both sleep and reducing jet lag symptoms.

Question: How was it discovered
Self-contained rewrite: How was melatonin discovered?