Alcohol is most easily absorbed through the first part of the bowel after the stomach - the duodenum - and anything that slows the passage of alcohol through the stomach will reduce the rate at which it is absorbed.
Having a full stomach (after a meal) is the easiest way to do this and explains why people get drunk quicker if they drink on an empty stomach.
It also makes a difference which tipple you prefer - very strong drinks (straight spirits) tend to slow the emptying of the stomach, while dilute ones (beer) tend to take longer to get through because of their volume.
Drinks in between, such as wine and spirits with mixers, are the most rapidly absorbed and, unit for unit, will tend to get you drunk more quickly.
Some alcohol is absorbed from the stomach, and there is an enzyme in the stomach wall that breaks some of it down before it ever reaches the blood stream.
Interestingly, women tend to have lower levels of this enzyme, which combined with the fact that they are generally smaller than men, accounts for why, unit for unit, they tend to get drunk more quickly.
Heavy drinking increases the risk of cancer of the gullet and stomach, ulcers and gastritis (inflammation of the stomach causing indigestion).