If you or your girlfriend is too uptight then it sounds a great idea to have sex while you are drunk. It makes both of you loose and curious, so it can give you both an unforgettable experience. However, if you are not attentive enough, you can say goodbye to all the pleasant moments quickly. What makes the difference is usually the amount of alcohol in your blood.
If you have one or two glasses of wine, or a couple of shots, it is usually the perfect amount, depending on your weight. Keep in mind that the less you weigh, the less you need to drink to feel relaxed. Also, the level of alcohol is higher in mature adults and in women. So, if a woman drinks the same amount as a man, she might get drunk, while he only feels a little intoxicated. And it is the same if a mature person drinks with a company of young adults.
It can mean that they cannot get hard or wet enough for sex, or even if they do, it will be a lot harder for them to reach an orgasm. In fact, a lot of people find it impossible with such a state of mind. However, with the right amount, inhibitions disappear and you can expect to have a loose, relaxed and wild experience that both of you will enjoy and will remember for a long time. So, as long as you know when to put the glass down, go for it!