S.L.
My first question to you would be, have you ever given your son Benedryl before? Benedryl either will knock a kid "out" (meaning he'll sleep great!) or make him wired (meaning giving him the equivalent of a cup of coffee!) Obviously, you wouldn't want to try giving a new med to your child without knowing what kind of reaction he is going to have it. (especially if there is a chance it could give him a ton of hyper energy on an airplane trip!) I have friends/family members who swear by Benedryl before a plan trip and those who wouldn't think of it. It totally depends on what you feel is appropriate. I, myself, think you should do whatever it takes to get you and your child through a plane trip. Even if its giving your child a snack every hour to keep him content. Or giving him a "treat" that you wouldn't normally allow to keep him content. OR letting him watch video after video for a long plane trip if it means keeping him content! My husband and I will be taking our twins (who will be 19 months at the time) on their first plane ride in May, and I am fully prepared to do whatever it takes to make for a successful 5 hour flight! (within reason of course!) Best wishes!