Melatonin is a naturally occurring substance in the body. It is what puts our bodies to sleep. The house managers in the group homes in my area are on 7 days then off 7 days. They sleep during the nighttime but it ends up being a very light sleep since they are basically listening for the group home members and if there is any noise.
They say they take it the first night they get off but still don't sleep well. They take it again the second night and sleep hard. Then they don't use it again until they are off work again the next time.
I would talk to a pharmacist. They are the experts when it comes to medications. Doc's don't know squat about meds, they only know what the drug reps tell them when they leave the samples.
I never trust anyone but a pharmacist and usually not even the ones at Walmart or Walgreens. I trust the ones where they actually make meds, a compounding pharmacy. Most mom and pop type of pharmacies will have more knowledge since they do more than just read a paper and count pills. A true pharmacist is one who can take a little of this and a little of that, combine it and turn out a good ointment or a cough syrup that is especially made to order for your needs.