I am not sure going 'cold turkey' works for me. There has got to be some balance in life between pleasure, determination and outcome. We all suffer from the 'dozies' from time to time (which could be any number of factors, really). Personal experience agrees with the above posts - best outcome is to start without sleep dept - - trouble with that, is it can be difficult to really know your own circumstances.
Apart from that, I find chewing gum helps and recently found on the Brimstone that 'Japanese rice crackers' found at one of the controls (Beaminster Coop) did a good job of being me awake.
Caffiene?? - Well, obviously we would all like to see one of those Vespa tri-scooter-van Barristers on the side of every lane:
However, short of that non-reality on the road, I have tried caffeinated chewing gum:
https://www.blockheadenergy.com/energy-gum-peppermint50mg caffeine per gum (they say about one single espresso). I find 2-3 takes the edge off the night an gets me through. And the argument foes that most of the caffeine is absorbed through the gums, so no upset stomach.