Is it permissible to take antihistamines without certification?

First, please remember, that anyone with a life-threatening condition should take whatever medicines are necessary without hesitation. In general, tablets are preferable to liquid medications which may contain problematic ingredients.  If no tablet alternative is available, the liquid should be diluted in water, juice or any liquid by a ratio of one to six, which is one ounce of liquid to one teaspoon of medication. This ratio should be done only in consultation with your doctor.