I have tried 5 mg melatonin for 3 days prior to my arrival in the US on previous transpacific flights.I must say that I have been a little disappointed with the results.
A small but signifigant reduction occurred in jet lag symptoms but I , on 2 occasions , I had quite severe memory loss ( funny to my friends at the time)
The origin of the "jet lag" syndrome is , I think , quite multifactorial. Sure ,after the transpac haul, there is day / night disorientation (for me worst going east ) but there is also the difficulty having any kind of reasonable sleep, there is dehydration (remember the aircraft is pressurised to 10,000 feet ), ? alcohol indulgence, and alteration in usual caffeine intake ( I would normally have 7 cups of tea per day )
I make an effort to go to sleep on the plane at the bedtime at my destination ,PLUS, on arrival , to walk in the sun , drink a couple of cups of tea and stay awake as long as possible the day of arrival.That night ,I take some form of benzodiazepam type sedative (eg oxazepam or temazepam )to ensure that I don't get wide awake at 2 AM and stay that way.
I do not think that there is an easy answer.
One thing I am certain about is the necessity to take some form of anti blood clotting drug to avoid leg clots (which are painful and debilitating enough )but can lead to an early demise from lung blood vessel obstruction.These tablets,such as low dose aspirin, need to be started a few days prior to departure as they only work on platelets formed after the tablets have been started.Of course there may be medical reasons why would not suit a particular individual .The other option is to wear anti embolism stockings ( they don't look good though if you are in short trousers)
Please excuse me going on and on here!
Ozflier