I have been taking Zyrtec D for many, many years and could not function without it plus Nasacort, Singulair and Topomax (and Immitrex). My 8 year old takes Claritin and Singulair (since he was about 3?) and my 3 year old takes Claritin. I don't think I'd put a 16 month old on Singulair. I don't think I'd put a 16 month old on anything. I didn't think you could put a child younger than 2 or 3? on Singulair. Back to the original post....I don't really know why I take the Singulair all the time. It only seems to help when my allergies get at their worst. A couple of times a year I get laryngitis. This is when the Singulair helps. I do have bad migraines all the time, but I don't know if it is from the Singulair or not. My son doesn't complain of any side effects.