well, it depends.
I was once told that antihistamine ( as in daily piriton) was not a good idea in the long term. For instance if a reaction to a food occured, the reaction may be mild, but as effect of antihistamine wears off, there was a chance of another stronger reaction later on.
But, I am not sure if this in all honesty is accurate.
My son did have side effects from piriton, headaches, nausea and being drowsy, lack of appitite
as he has always been underweight, lack of a calories is a big issue.
I am also questioning the ongoing need for antihistamine, as it may hinder proper dignosis of all allergies.
What are your childs allergies, both food and environmental?
If environmental, have other methods in home reduce the irritation of these allergies?
On another note, there are MANY 2nd generation antihistamines that dont have the same side effects.
However, they do produce others. It may take some time to find one, but there should be a daily one availble that suits your child.
My son has had problems with two 2nd generation antihistamimes, claritin and zytec.
Claritin, was an allergic reaction , and the zytec severely affected his mood.
You might consider that your sons personality may dramtically change when you remove antihistamine from his life.
I certainly did notice my sons increased enjoyment of life , once he was taken of this daily drug.
I wish you good luck