Alcohol's effects on the body are numerous and wide-ranging. Sexual activity can also have a range of effects on the body, including positive and negative ones. When we combine the two-- we have a whole world of things to consider. So let's dive into a few of them.
Alcohol is a depressant. This means the functioning needed to be sexually active is "turned off" by the alcohol. Things like feeling a partner's caress can go completely missed by the effects of alcohol.
A known dehydrator, alcohol can reduce the body's natural ability to self-lubricate or produce an erection.
Alcohol impairs motor function and memory-- which could make having sex under the influence more likely to increase the chances of not using protection at all or not using protection properly. For example, a person may remember to put a condom on a little too late or not at all.
Alcohol also impairs a person's judgment and perception of situations. This is particularly important when we think about consent. According to the law, those who have been drinking cannot legally give consent to sexual activity. If a situation arises and you aren't sure if someone is consenting to what's happening, it's safest to assume they are not consenting and don't engage further. Sex without consent is not sex, it's rape.