Final answer:
To adjust to a new time zone, Eric can administer a melatonin supplement to regulate his sleep cycle.
Step-by-step explanation:
When traveling across multiple time zones, a person may experience jet lag, where they feel sleepy during the day and awake at night. This is because the light-dark cycle regulated by melatonin is disrupted. To help adjust to the new time zone, Eric could administer a melatonin supplement. Melatonin is a hormone that regulates circadian rhythms and can help induce sleep.