1. The short answer
A 500 mL can of 9% chuhai (a Japanese canned spirit-and-soda drink) looks like one can, but it holds 36 g of pure alcohol. You can work that out with the formula Japan's Ministry of Health, Labour and Welfare uses: volume (mL) × ABV × 0.8. [1]
Kirin Ichiban Shibori, a popular Japanese beer, is 5% alcohol. [2] A 350 mL can of it has 14 g of pure alcohol, so a 9% 500 mL can equals about 2.6 cans. In 5% beer terms, that's roughly 900 mL, or about 1.8 of the 500 mL cans.
So "I only had one can" is a statement about the container. Your body is quietly logging it as "today's alcohol: just under three beers."
2. Why "5% is fine, but the big 9% can wrecks me" makes total sense
The gap isn't just the four percentage points between 5% and 9%. The total amount depends on strength × volume.
| Drink | Pure alcohol | Compared with 9%, 500 mL |
|---|---|---|
| 5%, 350 mL | 14 g | 1 |
| 5%, 500 mL | 20 g | 1.43 |
| 9%, 350 mL | 25.2 g | 1.8 |
| 9%, 500 mL | 36 g | 2.57 |
If your usual drink is a 5%, 350 mL can, then a 9%, 500 mL can is about 2.57 times as much.
It isn't "a slightly bigger can with a slightly higher ABV." It's a whole squad of reinforcements wearing a single can's face.
3. Why you can fall asleep fast and still sleep badly
Alcohol is a sedative, so you may drop off sooner. But falling asleep fast doesn't mean you slept well.
A 2024 systematic review and meta-analysis found that even low doses reduce REM sleep (the stage where most vivid dreaming happens). At high doses, people fall asleep faster, but the disruption to REM later in the night may get worse. [4] The NIAAA (the US National Institute on Alcohol Abuse and Alcoholism) also says that after drinking it's easier to fall asleep, but sleep becomes fragmented and you tend to wake up early. [3]
Older sleep research reports a pattern too: REM is suppressed in the first half of the night, then as the alcohol wears off you wake more often in the second half. In some people REM bounces back more than usual, which can bring vivid or anxious dreams. [9]
Here's the important part: drinking doesn't always cause REM rebound. What the research as a whole supports strongly is that "alcohol disrupts the structure of your sleep." Whether the dream cinema opens up varies from person to person.
4. Dreams that blur with reality, and characters or problems that get "installed" without asking
In a dream, you accept things that would make you stop and say "wait, that makes no sense" if you were awake. Sleep research also describes dreams as immersive, with bizarre content that tends to be accepted as is. [5]
On top of that, right as you fall asleep or wake up you can get hypnagogic or hypnopompic experiences (vivid perceptions at the edge of sleep). People, faces, scenes, sounds, and body sensations can feel extremely real, and this can happen even to healthy people. [5][6]
So all of these:
- You think the dream is real while you're in it
- Settings and characters get added on their own
- You're forced to work through some problem endlessly
- The moment you wake up, you know it was all a dream
are fairly easy to explain as phenomena of sleep, or of the border between sleep and waking.
It's a different story if images or voices continue in broad daylight while you're fully awake, if you can't tell what's real even after waking, or if sudden severe confusion appears. Don't brush those off as just "an intense dream."
If the brain's screening room only runs while you sleep, it's the dream department's job. If it keeps screening after you're awake, that's a case for a different department.
5. Can aching legs, not a headache, be a hangover?
Yes, it can. The NIAAA lists typical hangover symptoms as fatigue, weakness, thirst, headache, and also muscle aches. [3]
Blaming it all on dehydration is too simplistic. The NIAAA names several factors: mild dehydration, disrupted sleep, inflammation, stomach irritation, and exposure to acetaldehyde (the toxic by-product your body makes when it breaks down alcohol). [3]
In other words, there's a very plausible route:
Alcohol → you lose fluids more easily + your sleep falls apart + inflammation kicks in → fever-like heaviness and muscle aches
That said, it's risky to write off every strong muscle pain as "just the booze."
6. No jokes for this part: warning signs
The CDC lists the main signs of rhabdomyolysis (a condition where muscle tissue breaks down and floods the blood) as muscle pain stronger than you'd expect, tea- or cola-colored urine, and severe weakness or fatigue. [7] Symptoms alone can't confirm it. You need a blood test, such as CK (creatine kinase, a muscle enzyme), at a medical facility.
Also, if after drinking you have severe confusion, repeated vomiting, seizures, slow or irregular breathing, or you pass out, treat it as an emergency sign of acute alcohol poisoning. [8]
So when your legs hurt, the checks are simple:
- Is your urine a normal color?
- Can you walk normally and put force into your legs?
- Is the pain getting worse quickly?
- Do you have a fever or feel seriously unwell?
- Even after waking up, are your consciousness and sense of reality off?
If any of these is clearly abnormal, this is not the time to be reading a hangover article.
7. What to do: there's no cheat code for a hangover
The NIAAA's conclusion is pretty merciless: there's no magic cure for a hangover, and mostly it just takes time. [3]
In practice, the basics are:
- Don't drink any more
- Sip fluids little by little
- Eat something light if you can
- Avoid hard exercise
- Rest or sleep if you can
- Don't drive or do dangerous work
Coffee, a shower, and a "hair of the dog" (more alcohol the next morning) won't speed up your brain's recovery. [3] Sports drinks work fine as "fluids that are easy to drink," but there's no evidence that adding electrolytes cures a hangover any faster. [3]
Don't casually pile on painkillers either. The NIAAA warns about liver toxicity when alcohol is combined with acetaminophen, and about stomach irritation from aspirin, ibuprofen, and similar drugs. [3]
8. To prevent a repeat, count grams of pure alcohol, not cans
The most practical fix is this one:
volume (mL) × ABV × 0.8 = pure alcohol (g). [1]
If 5%, 350 mL cans rarely cause trouble but 9%, 500 mL cans wreck you every time, that's useful practical information: at least for your body, your reactions around 14 g and around 36 g are different.
That doesn't mean 36 g is a danger line for everyone. The effects of alcohol vary a lot with body size, metabolism, drinking speed, food, lack of sleep, medication, and how you feel that day.
That's why asking "How many grams did I take in?" is far safer than asking "How many did I have?"
9. Wrap-up: please stop letting a 9% big can cosplay as one can
A 9%, 500 mL can is 36 g of pure alcohol. That's about 2.6 cans of 5%, 350 mL beer.
At that amount, a sequence like this is entirely possible:
You fall asleep easily
→ your sleep structure gets scrambled
→ the second half of the night is chopped into pieces
→ your dreams may get oddly intense
→ your dream's reality check goes on break
→ in the morning, even your muscles are asking "what did you do yesterday?"
The takeaway: before deciding "I'm just terrible with alcohol," understand that a big 9% can simply contains a huge total amount of alcohol.
One can.
Inside, just under three beers.
Don't count alcohol by the number of containers.
