Sleep is one of the most important activities for our health and wellbeing. In fact, we can’t live without sleep. But when we’ve had one drink too many, we don’t seem to get enough of it. So what happens when alcohol interferes with your sleep?
We have all experienced it: a little booze has been experimentally and anecdotally demonstrated to help us fall asleep faster and increase deep sleep in the first half of the night. But the impact of alcohol has a dual relationship with sleep: it can make us feel sleepy initially while intoxicated and it can disturb our sleep as it wears off.
In fact, as many as 20% of Americans use alcohol to help with falling asleep — but its effects on other aspects of sleep—notably, the second half of the night—leaves little to be desired.
If you imbibe too much close to bedtime, both the quality and quantity of your sleep ― and your brainpower the next day ― will suffer. As a matter of fact, lack of quality sleep is one of the main symptoms of alcohol hangovers.
So how exactly does drinking alcohol affect the quality of our sleep? Let's take a look at some of the reasons why it's so damn hard to sleep in after a drunk night on the town.
1. IT CAUSES THE “REBOUND EFFECT”
Even moderate alcohol consumption can ruin a good night's sleep. For instance, a modest dose of alcohol (Blood Alcohol Content in the range of 0.06–0.08) within an hour of bedtime may knock you right out — but it'll exact a serious toll on your body during the second half of your normal sleep period, during what's called a "rebound effect". But what exactly constitutes the so-called “rebound effect”?
In case you forgot, alcohol totally counts as a drug, and your body has to adjust for its effects — like the production of sleep-inducing adenosine and inhibition of the excitatory neurotransmitter glutamate— when it enters your body. After the alcohol is metabolized a few hours later, these adaptations are now unnecessary, and your body is all out of whack. Needless to say, this can jolt you awake.
2. IT PREVENTS DEEP SLEEP
The stage associated with dreams and learning, REM (rapid eye movement) sleep is one of the most restorative parts of sleep - and it's reduced by alcohol. 3 Recent research shows that our dreams may play a crucial role in maintaining the normal function of human physiology and brain function. That’s because during REM, certain neurotransmitters like serotonin are effectively switched off, so we use this period of our sleep pattern to replenish or reset these vital brain chemicals. While low and moderate doses of alcohol seem to have little effect on REM sleep, high doses of alcohol have a significant impact on the amount and duration of REM.
In other words, not only are you more likely to wake up thanks to the rebound effect, but you're also missing out on the most restorative stage of shut-eye. This can leave you feeling tired the next day no matter how long you stay in bed. No wonder hangovers make you feel tired, sluggish and stressed.
3. IT INTERRUPTS SLEEP FOR TRIPS TO THE BATHROOM
When you drink more than usual, you may often have to get up in the night to go to the toilet. That’s because alcohol is a potent diuretic and makes you urinate more than you would when drinking the equivalent volume of non-alcoholic drinks. According to one study, for every 1g of alcohol drunk, urine excretion increases by 10ml. 
The reason this happens because alcohol suppresses a hormone known as vasopressin (anti-diuretic hormone) which regulates the amount of water absorbed by the kidneys. When vasopressin is low, instead of storing water, the kidneys dump it into the bladder, causing the urge to pee.
This creates a very strong urge to make repeated trips to the bathroom – making for some potentially very sleepless nights.
4. IT AFFECTS WOMEN MORE
A 2011 study into the effect of intoxication on healthy young adults found that alcohol disrupts sleep efficiency in women more than in men.6 These gender differences could be explained by the fact that women metabolize alcohol more quickly than men, meaning that the sedative properties of a late-night drink wear off more easily, causing women to feel the second, more fragmented part of their sleep more quickly.
In summary, the study found that women had fewer hours of sleep, woke more frequently and for more minutes during the night, and had more disrupted sleep than men.
SLEEP & ALCOHOL: THE BOTTOM LINE
A 2013 review of 27 published studies found out that alcohol reduces the time it takes to fall asleep and increases the amount of deep sleep during the first half of the night. However, this is offset by increased sleep disturbances in the second half of the night. 
So, if you plan on having more than one drink, you may be looking at some pretty serious bedtime disturbance. And that’s mainly because alcohol may seem to be helping you to sleep, as it helps induce sleep, but overall it is more disruptive to sleep.
But it’s not all bad news. According to research, a nightcap does help you fall asleep faster; as long as you stick to just one drink, it's been shown to improve sleep quality and duration.
It’s clear that alcohol does affect the quality of your sleep, but there are many factors that go into just how much it affects your slumber. It can cause an array of sleep disruptions, from causing “the rebound effect” and preventing deep sleep, to causing you to wake up multiple times during the night to use the restroom. If getting a good nights sleep is important to you, it may be beneficial to watch your alcohol intake the night before.