And why doesn't he know about it? Don't they ask you each time if your meds have changed? And you should tell him. That being said, allergy docs are prescribing Singulair for allergies even though that isn't what it was intended for. I go to an immunologist in an allergy clinic for my allergies and asthma. We tried adding it to my other meds when I started have allergy trouble when mowing the grass...Zyrtec wasn't getting it under control. However, the Singulair did not work for me so we stopped it. And I was on immunotherapy at the time...administered by him so obviously it wasn't a problem to take Flovent, Albuterol, Zyrtec and Singulair while taking the shots.