Few months ago some supermarket had their cheap own make energy drink on sale, friend of mine was drinking two 1 litre bottles a night mixing it with a bit of vodka. This went on for about a week and then I had the following conversation with her.
Her: Got a doctors appointment booked this afternoon
Me: Nothing serious I hope
Her: Dont think so, not been sleeping the past few days, just dont feel tired when I go to bed, then I dont sleep and ofc tired the whole of the next day
Me: Probably the 2 litres of energy drink you are having before you go to bed

Her: Dont be silly
After the appointment
Her: Been given some sleeping tablets, doctor told me to lay off caffeine during the evenings but I only have a cup of coffee in the afternoon
Me: and the 2 lites of energy drink before you go to bed
her: *Sigh* its not that
Then had a couple of days of her saying tablets werent doing anything, was feeling tired after taking them but still couldnt sleep and felt worse in the morning. Couple days later and the energy drink is no longer on offer so she switches to cranberry juice with her vodka as that is on offer, suddenly as if by magic the sleeping tablets are working