Zyrtec (cetirizine) works best for me but also is very sedating for the next 24 hrs. can i split the pill and take a lower dose (5 mg) or even 2.5 mg children's dose? would those doses be less sedating?

Yes: But at your age it probably won't work very well either!

Antihistamines: Yes, you can try a lower dose. It may not have the same effect on your allergies as the full dose, however there should be no harm in trying. Fexofenadine and loratidine are other options that are non-sedating. These may be options for you as we'll. Good luck!

Yes: An effective dose varies on each individual. You may perfectly try a lower dose to see if it is still effective, and gives you less side effects (drowsiness). Start by going down to 5 mg. If the "trade-off" is not good, you might have to try xyzal (levocetirizine) (prescription med).

Possibly but...: Decreasing the dose may also decrease the sedative effects. But it will presumably also decrease the main effects as well. Consider trying other medications, and also ensure that you are not taking zyrtec (cetirizine)-d which is more sedating that zyrtec (cetirizine).