It’s probably no surprise to hear that caffeine helps jet lag – but scientists have found that, oddly, it only helps if you’re going west.

The study, published in Science Translational Medicine, shows that caffeine tricks your body into thinking it’s actually an hour earlier than it really is. Your melatonin levels will increase at a delayed rate, allowing you to stay awake a little longer and adjust to a new time zone.

So setting your body clock back by an hour is useful when going west, but if you’re heading east, the timing won’t work, making it harder for you to sleep.

The upshot? If you’re heading to Perth, drink up. Sydney? Stick to decaf.