Dark drinks contain more congeners which make them more likely to cause hangover symptoms. Congeners however do not have an effect on how much one can drink, only the likelihood of getting a hangover. Not everyone is sensitive to congeners, but they are a biproduct of the fermentation process. Clear alcohols like gin and vodka have very few, whilst bourbon and red wine tend to have the most. Beer is somewhere in the middle, generally having more for a darker beer.
