For how long i should use zyrtek? is it safe for a long term use? (been using them for a few days)

About cetirizine: The dose recommended is 10mg each day for older children or adults. Zyrtec (cetirizine) causes some people to have some sleepiness, but in general does not make people sleepy. With a higher dose (10-20mg), there isn't much information about whether or not it increases sleepiness. Zyrtec can be taken daily only when allergy symptoms arise but some people take it all allergy season (about 3 months).