I was pretty young when I had my first son (not awfully young, but at 23 I think I was still pretty green) anyway, when he was 15 months we were going on holiday to Greece.
I am NOT a good flyer, I hate it beyond all reason. I was worried about DS and worried about myself TBH. A friend told me (a mother of 2 at this point) to "just give him a dose of phenergan (Sp?) and he'll be fine, he'll sleep and you can get on with it"
I took her advice and did so. I gave him the phenergans and within 20 minutes he was as white as a sheet and just conked out. Not in a sweet "aw, look he's asleep!" way in a "fuck, is he ok?" way.
So, instead of having made a stressful situation easier I had actually made it a million times worse, I was SO WORRIED about him, so, so, terribly worried.
He was fine. Was it worth it? No.
Would I do it again? No.
I have smiled through all of our flights since (this is a lie , I cry and hate every fucking second, but I'm phobic ) and would never NEVER give my children a drug in order to pacify them (unless it was prescribed by a Dr for something serious IYKWIM)