Vallergan
First papa from the first result for Vallergan...

Vallergan tablets, syrup and forte syrup all contain the active ingredient alimemazine (previously known as trimeprazine in the UK). Alimemazine is derived from a group of medicines called phenothiazines, and is a type of medicine called a non-sedating antihistamine. (http://www.netdoctor.co.uk/medicines/100002712.html)

But then later ...
Alimemazine is called a sedating antihistamine because it enters the brain in significant quantities and causes drowsiness.

Alimemazine is also used as a pre-med in children to produce sleepiness before operations. It is given one to two hours before the anaesthetic.
( 0nyx, Fri 14 Sep 2007, 16:14, Reply)