A medical statement of the obvious

I've had maybe 10 hours proper sleep in the last week. As a result, my Doctor has prescribed me some sleeping pills, Promethazine Hydrochloride.

I collected them from the chemists on the way home from work and have just opened the packaging. Instructions are:

Take ONE at night
WARNING. THIS MEDICINE MAY MAKE YOU FEEL SLEEPY...

Really? Pills I'm supposed to take at night to make me go to sleep may make me feel sleepy and I need to be warned?

Thanks, wouldn't have figured out that sleeping pills might make me sleepy...

(Ok, the rest of it is the standard don't drive or do silly things after taking it, but, really, they actually need to warn people this?)