Alcohol and sleep: what happens in the second half of the night
Partilhar
Alcohol puts you to sleep faster and makes you sleep worse. Both are true at the same time. If you wake up at 3 in the morning after two glasses of wine at dinner, it is not a coincidence — it is what happens when the alcohol leaves your system. I will explain what happens in each half of the night and what you can adjust.
First half: the sedative effect
Alcohol acts on the GABA-A receptors, the same ones sedatives act on. It reduces the time you take to fall asleep and increases slow-wave sleep in the first two to three hours. That is why the initial sensation is good and that is why so many people use a drink to get to sleep.
The problem is that this is only the first half.
Second half: the rebound
The body metabolises about one drink per hour. When the alcohol is gone, the nervous system responds with hyperactivity — the opposite of the initial sedation. Body temperature rises, heart rate speeds up and sleep breaks into short awakenings that you often do not even register.
The result: you spend seven hours in bed and wake up feeling like four.
REM is the first to be cut
A meta-analysis published in Sleep Medicine Reviews measured a reduction of 11.3 minutes of REM sleep on a night with alcohol, compared with the same person without alcohol. And the effect is dose-dependent: for each gram of alcohol per kilo of body weight, the reduction reaches 40.4 minutes. For someone of 70 kg, 1 g/kg corresponds to about five or six drinks.
REM is the phase associated with memory consolidation and emotional processing. Cutting it explains the part of the tiredness that more hours in bed does not solve — and it also explains why the day after a night of drinking carries more irritability than the number of hours would justify.
Snoring and apnoea: alcohol makes both worse
Alcohol relaxes the muscles of the upper airway. People who snore, snore louder and for longer. People with sleep apnoea — diagnosed or not — have longer and more frequent episodes in the hours after the last drink.
If this sounds familiar, read sleep apnoea: signs, risks and what to do first. It is the only point on this list that warrants a medical appointment rather than adjustments at home.
How long before bed
Rule of thumb: three hours between the last drink and bed. For each drink above two, add an hour. It is not a clinical rule, it is metabolic arithmetic — the later you drink, the greater the overlap between the alcohol elimination phase and the sleep window.
Two notes that tend to surprise people:
- The digestif after dinner does more damage than the glass of wine during the meal, even if the total amount is the same.
- Drinking less but later does not compensate. The time matters as much as the dose.
What to adjust this week
- Last drink three hours before bed. It is the adjustment with the highest return and the easiest to test in seven days.
- One glass of water for each drink. It reduces awakenings from thirst and from trips to the bathroom in the second half of the night.
- Bedroom between 16 and 19 °C. Alcohol raises body temperature precisely in the phase when the body needs to cool down. The figures are in ideal bedroom temperature for sleeping.
- If you snore after drinking, sleep on your side. The side position reduces airway collapse. You need a pillow with enough height to keep the neck aligned with the spine — the range is in pillows for side sleepers. The Kaiteki (快適, "comfort") was designed for that profile.
- Do not swap alcohol for a supplement without understanding what you are treating. I compared the two most used ones in magnesium or melatonin.
If you want a fixed sequence for the two hours before bed, the night routine guide has the step by step. And if the basics are not sorted yet, start with the sleep hygiene guide.
When it stops being a habit
If you need alcohol to fall asleep, the problem is no longer the drink — it is the insomnia behind it. Tolerance to the sedative effect sets in within a few weeks and the insomnia worsens when the alcohol is withdrawn, which closes the loop. At that point, solving it alone is rare.
Before you change anything
This article is informative and does not replace medical advice. If you have chronic insomnia, diagnosed sleep apnoea, take sleep medication or use alcohol regularly to fall asleep, talk to your doctor before making changes.
If your night breaks in the middle and you suspect the mattress or the pillow is contributing, talk to me. Ten minutes on the phone is enough to find out. The contact is on Sleep Adviser.
— Ana Cristina, Sleep Adviser at Dreamura
