If you think that single in-flight cocktail is the reason you're red-faced and giddy, you may want to blame it on onset vacation excitement.
In the 1930s, American psychologist R. A. McFarland discovered that two to three drinks enjoyed at 10,000-12,000 feet (an even lower altitude than an airplane cruising high above the ground) is the equivalent of four to five enjoyed at a table in a restaurant at sea level. McFarland's study looked into the effect of changes in oxygen tension paired with a number of variables, including alcohol intake. He eventually wrote about his findings in a published piece called “High Altitude: An Exploration of Human Adaptation.”
But, as Slate points out in a deep dive they did into the topic, there hasn't been a lot of scientific evidence behind McFarland's work since it was published. In his defense, he wasn't necessarily out to apply this logic to a plane ride.
So, what's the deal? Would this also mean that McFarland thought we would get drunk quicker on an airplane than at home? It depends on whether or not your flight is going according to schedule.
First off, engineers and airline crews work hard to make sure the cabin pressure is similar if not exactly the same as the air we enjoy from solid ground, according to Aviation StackExchange. Sure, it might be a bit drier, but it certainly gets the job done.
When you drink alcohol, it gets into your bloodstream and its presence makes it harder for your body's hemoglobin to absorb oxygen, according to Gizmodo. So, the idea that a higher altitude will not only make it harder to get enough oxygen without alcohol, but even tougher with a few drinks in your system, is valid. But, as mentioned above, an airplane cabin has plenty of fresh air. You would have to be floating outside the airplane, maybe hanging out on the wing, without any access to oxygen for McFarland's logic to work its magic on you. But if that were the case, you wouldn't be making it to your final destination.
In short: No, you're not going to get drunker on an airplane just because there's more space between you and the ground. It's a different story if you're climbing a mountain or partaking in another activity that would call for altitude acclimation. A study in the Annals of Internal Medicine tested out this theory with 10 male climbers, giving them 1.7 ounces of alcohol at two different altitudes: 561 feet above sea level and 9,842 feet as they climbed the Austrian Alps. It was found that drinking alcohol can make acclimating to higher altitudes tougher, meaning altitude sickness is easier to come by.
So, the conclusion: You're not going to get drunk any quicker on an airplane than at home. But if you find yourself climbing a mountain and you don't want to suffer the terrible side effects of altitude sickness (headaches, loss of appetite, sleeping issues, nausea, weakness, tiredness, dizziness, and lack of energy, according to WebMD), steer clear of partying.