This I learned a few days ago. First the scene set.
In France, the day before driving back to the UK, requiring 1200km driving in a day. I would like to ensure a good night sleep, for obvious reasons. I have a streaming cold. I have bought some cold remedy from a French Pharmacy, with pills marked "Day" and "Night". Not wishing to knock myself out for an early start, I choose a "Day" capsule, thinking I will get a good night sleep. Two hours later I have come to the conclusion that the "Day" capsules have an over-quantity of caffeine, as I am more than a little wired and sleep is a distant dream (only it isn't a dream, clearly). Which is odd, as my tolerance for caffeine is high. Oh well.
It is the day after return I learn that the French cold remedy decongestant is amphetamine, with the night dose being a fraction of the day dose. Oh well.