I wouldn't, as it can supress respiration or something. And yeah, it can have the opposite effect - My sister, 2 years old, ballistic on a flight to the UK
Are you still breastfeeding? You might find that's the best thing. We took DS to NZ when he was 20 months (so bit older) and I was really worried, but he was actually great on the plane! The only time he went a bit feral was when we had an evening flight and he missed bedtime. (and even then he just kept insisting on changing seasts and putting his seatbelt on andn off, on and off....)
Make sure you have snacks, books, toys and be willing to walk the aisles. Will they have tvs on the plane?
Hope you have a great trip