Answers.Body: <p>Well, this question might get closed as a duplicate, but I'm going to answer it anyway, and try to answer it better. IMO, the suggested duplicate answers a <em>different</em> question, only answering the hydration question too, by side-effect. Personally, I like <em>this</em> question paired with <em>that</em> answer, better than <em>that</em> question.</p>
  
  <h3>tl;dr — Alcohol is a diuretic (defined: <em>a substance that promotes the production of urine</em>), causing you to expel more water than the body would normally expel.</h3>
  
  <p>That much has been shown conclusively.</p>
  
  <blockquote>
    <p>If sufficient alcohol is ingested, the diuresis occurs at the expense of all cellular components, and dehydration ensues.</p>
  </blockquote>
  
  <p><sup><a href="http://archinte.jamanetwork.com/article.aspx?articleid=568848">Roberts, K. E. Mechanism of Dehydration Following Alcohol Ingestion. 1963. [Abstract (HTML)]</a></sup></p>
  
  <p>As far back as the 1930s, researchers were trying to understand whether alcohol—the substance itself—is a diuretic, or indirectly induces chemicals which are diuretic (or which inhibit antidiuretics) or triggers cortical functions that cause diuresis.</p>
  
  <blockquote>
    <p>[Most] writers either state categorically or imply that alcohol per se has no diuretic action. In 1932, however, from a comparison of the diuretic effects of a given volume of water, with and without alcohol, [...] Murray concluded that alcohol itself was exerting a diuretic action. [...] The diuretic action of alcohol has now been demonstrated on five other subjects, and its mode of action investigated [...]</p>
  </blockquote>
  
  <p><sup><a href="http://jp.physoc.org/content/101/2/172.full.pdf">Eggleton, M. G. The Diuretic Action of Alcohol in Man. 1941. [Full Paper (PDF)]</a></sup></p>
  
  <p>The first paper (1963) actually confirmed that <strong>alcohol—yes, ethanol itself—inhibits antidiuretic hormones, causing diuresis, causing dehydration.</strong> (Caffeine does this too, by the way.)</p>
  
  <p>So, yeah. That's how that happens.</p>
  
  <hr>
  
  <p>Unrelated, but I found this interesting in the second paper...</p>
  
  <blockquote>
    <p>It [the diuresis] is initiated by the <em>increase</em> in blood-alcohol concentration and fails to be maintained if this concentration is kept steady, even at high levels [...] The diuretic response to alcohol differs markedly in one respect from that of the cerebral cortex. The latter is most affected by the <em>rate</em> of increase in blood-alcohol concentration: the greater this rate of increase, the greater the disturbance of function at any absolute concentration. The diuretic response, on the other hand, is dependent mainly on the <em>duration</em> of increasing blood-alcohol concentration and not on the rate of increase (Tables 6, 7). The naturally slow absorber, therefore, tends to give a larger diuretic response than the rapid absorber.</p>
  </blockquote>
  
  <p>The slower you get drunk, the more dehydrated you'll be!</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2014-02-01T10:19:08.893Z
Answers.LastActivityDate: 2014-02-01T10:19:08.893Z
Answers.UserDisplayName: Andrew Cheong
Body: <p>It's often recommended that you drink water before and during a heavy drinking session.  Why is it that, despite being mostly water, beer dehydrates you?</p>
  
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2014-01-31T22:01:20.093Z
Comments.Text: Crap, I think you're right.  Voting to close as duplicate.
Comments.UserDisplayName: Fishtoaster
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2014-01-31T22:03:13.617Z
Comments.Text: A bit of a shame, since I actually like your question better.
Comments.UserDisplayName: Xander
Tags: <drinking><water>
Title: Why does beer dehydrate you?
UserDisplayName: Fishtoaster
ThreadText: # Why does beer dehydrate you?
  
  (Asked by: username_0 on 2014-01-31)
  
  It's often recommended that you drink water before and during a heavy drinking session. Why is it that, despite being mostly water, beer dehydrates you?
  
  **Tags:** drinking, water
  
  > **Comments:**
  > **username_0**: Crap, I think you're right.  Voting to close as duplicate.  
  > **username_1**: A bit of a shame, since I actually like your question better.  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_2 on 2014-02-01. Score: 13
  
  Well, this question might get closed as a duplicate, but I'm going to answer it anyway, and try to answer it better. IMO, the suggested duplicate answers a *different* question, only answering the hydration question too, by side-effect. Personally, I like *this* question paired with *that* answer, better than *that* question.
  
  ### tl;dr — Alcohol is a diuretic (defined: *a substance that promotes the production of urine*), causing you to expel more water than the body would normally expel.
  
  That much has been shown conclusively.
  
  > If sufficient alcohol is ingested, the diuresis occurs at the expense of all cellular components, and dehydration ensues.
  
  [Roberts, K. E. Mechanism of Dehydration Following Alcohol Ingestion. 1963. [Abstract (HTML)]](http://archinte.jamanetwork.com/article.aspx?articleid=568848)
  
  As far back as the 1930s, researchers were trying to understand whether alcohol—the substance itself—is a diuretic, or indirectly induces chemicals which are diuretic (or which inhibit antidiuretics) or triggers cortical functions that cause diuresis.
  
  > [Most] writers either state categorically or imply that alcohol per se has no diuretic action. In 1932, however, from a comparison of the diuretic effects of a given volume of water, with and without alcohol, [...] Murray concluded that alcohol itself was exerting a diuretic action. [...] The diuretic action of alcohol has now been demonstrated on five other subjects, and its mode of action investigated [...]
  
  [Eggleton, M. G. The Diuretic Action of Alcohol in Man. 1941. [Full Paper (PDF)]](http://jp.physoc.org/content/101/2/172.full.pdf)
  
  The first paper (1963) actually confirmed that **alcohol—yes, ethanol itself—inhibits antidiuretic hormones, causing diuresis, causing dehydration.** (Caffeine does this too, by the way.)
  
  So, yeah. That's how that happens.
  
  ---
  
  Unrelated, but I found this interesting in the second paper...
  
  > It [the diuresis] is initiated by the *increase* in blood-alcohol concentration and fails to be maintained if this concentration is kept steady, even at high levels [...] The diuretic response to alcohol differs markedly in one respect from that of the cerebral cortex. The latter is most affected by the *rate* of increase in blood-alcohol concentration: the greater this rate of increase, the greater the disturbance of function at any absolute concentration. The diuretic response, on the other hand, is dependent mainly on the *duration* of increasing blood-alcohol concentration and not on the rate of increase (Tables 6, 7). The naturally slow absorber, therefore, tends to give a larger diuretic response than the rapid absorber.
  
  The slower you get drunk, the more dehydrated you'll be!
  
  
  ---
  
  