I've been long haul since 1974, still doing it.
Life was hell for a few years trying to get to sleep until I discovered halcion tablets and it's been a breeze ever since. I've been using them for 30 odd years.
Problem is trying to get to sleep, once you're asleep no problem, so generally 1/4 to 1/2 a tablet does the trick.
I sometimes (depending on whether 3 or 4 crew) use them before a long haul night flight so if I don't sleep on board I can make it without having to resort to cockpit napping.