The last my company had to say on the subject was in 1993 when it put out a Crew Notice syaing that the only sleeping pill approved by the UK CAA was (is) Temazepam.
Apparently Temazepam is a 'Hypnotic' as opposed to a sleeping pill. I think the difference is that a hypnotic will relax you enough to put you asleep but will not keep you asleep. So if you take a temazepam, fall asleep and 20 minutes later the children come in and wake you up, you will actually wake up and not be in a drug dozy stupor.
From what I've been told, Temazepam was developed for Gulf War (1991) military pilots who needed to sleep during 'waking hours' to be ready for night missions. That forced the CAA to recognise and approve Temazepam. But since then they haven't approved anything else.
I find that taking one 10 milligram pill will give me a good 5 hours sleep, but to make the most of it, you need an empty stomach. The label always says take at least 10 hours before operating equipment.
Temazepam is now a controlled drug in the UK because druggies were getting the capsules, injecting syringes into them and drawing out the drug from the capsule, then injecting themselves with mega doses of the stuff to get some 'high'. Idiots.