You can take 2 different antihistamines at a time, if your doctor says it's OK. If you have a severe itchy skin rash, your doctor may recommend 2 different antihistamines together for a few days. You could take a non-drowsy antihistamine (such as cetirizine, fexofenadine or loratadine) during the day, and a drowsy antihistamine at night if itching is making it difficult to sleep. Do not take another drowsy antihistamine together with promethazine. It'll make you very tired and sleepy. Other drowsy antihistamines include chlorphenamine (Piriton) and diphenhydramine (Nytol Original). Important Do not take 2 antihistamines together unless you have been advised to by your doctor.